Basic and Clinical Sciences Examination (BCSE) — Questions and Answers

Question 1: Which of the following viruses uses reverse transcriptase and integrates a DNA provirus into the host genome, causing immunodeficiency in cats?

Feline calicivirus
Feline herpesvirus-1
Feline leukemia virus
Feline immunodeficiency virus (Correct answer)

Correct answer: Feline immunodeficiency virus

Feline immunodeficiency virus (FIV) is a lentivirus (retrovirus) that uses reverse transcriptase and integrates as a provirus, causing progressive CD4+ T-cell depletion.

Question 2: Which of the following correctly pairs a drug with its mechanism of causing QT prolongation via cardiac ion channel blockade?

Sotalol — blockade of the inward rectifier potassium current (IK1 encoded by KCNJ2)
Ibutilide — blockade of the L-type calcium current (ICaL) with secondary IKr inhibition
Amiodarone — blockade of the slow delayed rectifier potassium current (IKs encoded by KCNQ1/KCNE1)
Dofetilide — blockade of the rapid delayed rectifier potassium current (IKr encoded by hERG) (Correct answer)

Correct answer: Dofetilide — blockade of the rapid delayed rectifier potassium current (IKr encoded by hERG)

Dofetilide is a selective IKr blocker — it specifically targets the rapid component of the delayed rectifier potassium current, which is encoded by the hERG (KCNH2) gene. Blocking IKr delays ventricular repolarization, prolonging the QT interval and increasing the risk of torsades de pointes. Amiodarone broadly blocks multiple ion channels (IKr, IKs, INa, ICaL) rather than selectively IKs. Sotalol also primarily blocks IKr, not IK1. Ibutilide's primary mechanism is activation of a slow inward sodium current, not direct ICaL blockade.

Question 3: Which class of drugs causes hyperkalemia by blocking aldosterone's action in the collecting duct?

Osmotic diuretics (mannitol)
Loop diuretics (furosemide)
Thiazide diuretics (hydrochlorothiazide)
Potassium-sparing diuretics (spironolactone) (Correct answer)

Correct answer: Potassium-sparing diuretics (spironolactone)

Spironolactone competitively antagonizes aldosterone receptors in the collecting duct, preventing sodium reabsorption and potassium secretion, leading to potassium retention and hyperkalemia.

Question 4: Which lymph node is most accessible for palpation in a healthy dog and is routinely evaluated during physical examination?

Mesenteric lymph node
Mediastinal lymph node
Submandibular lymph node
Popliteal lymph node (Correct answer)

Correct answer: Popliteal lymph node

The popliteal lymph node, located in the popliteal fossa behind the stifle joint, is consistently palpable in dogs and is a standard part of the physical examination.

Question 5: A patient undergoing thyroidectomy is found to have a high-riding innominate artery. What is the anesthetic implication?

Higher risk of air embolism during dissection
Increased risk of arterial bleeding during tracheostomy (Correct answer)
Difficult airway due to tracheal deviation
Recurrent laryngeal nerve injury risk

Correct answer: Increased risk of arterial bleeding during tracheostomy

A high-riding innominate artery overlies the trachea at or above the sternal notch, creating significant hemorrhage risk during emergency tracheostomy.

Question 6: Which finding on a transtracheal wash or bronchoalveolar lavage is most consistent with eosinophilic bronchopneumopathy in a dog?

Greater than 25% eosinophils on cytology (Correct answer)
Predominance of lymphocytes
Charcot-Leyden crystals with mast cell degranulation
Neutrophilic inflammation with intracellular bacteria

Correct answer: Greater than 25% eosinophils on cytology

Eosinophilic bronchopneumopathy is characterized by eosinophilic airway inflammation, typically >25% eosinophils on BAL cytology.

Question 7: A veterinarian is advising a laboratory on housing for a group of non-human primates. To improve their psychological well-being, the veterinarian recommends implementing an environmental enrichment program. What is the primary goal of providing environmental enrichment to captive animals?

To decrease the overall food consumption of the animals.
To increase the ease of handling and restraint for procedures.
To provide opportunities for species-typical behaviors and cognitive stimulation. (Correct answer)
To ensure the enclosure remains sterile and free of pathogens.

Correct answer: To provide opportunities for species-typical behaviors and cognitive stimulation.

The primary goal of environmental enrichment is to enhance the quality of life for captive animals by providing stimuli necessary for psychological and physiological well-being. This involves creating an environment that allows them to perform species-typical behaviors (e.g., foraging, climbing), exercise cognitive skills, and have some measure of control, which helps to reduce stress and prevent the development of abnormal behaviors.

Question 8: A 4-year-old male neutered Doberman Pinscher presents for evaluation of exercise intolerance and a 2-episode history of syncope. Echocardiography reveals a dilated left ventricle with an internal diameter in diastole (LVIDd) of 6.8 cm, fractional shortening of 14%, and spontaneous echo contrast ('smoke') in the left atrium. No mitral regurgitation murmur is auscultated. Which hemostatic abnormality is MOST directly responsible for the increased thromboembolic risk in this patient?

Thrombocytopenia secondary to splenic sequestration
Hypercoagulability from concurrent protein-losing nephropathy
Blood stasis within the dilated left atrium promoting thrombus formation (Correct answer)
Decreased antithrombin III from hepatic congestion

Correct answer: Blood stasis within the dilated left atrium promoting thrombus formation

Dobermans with dilated cardiomyopathy (DCM) are at high risk for left atrial thrombus formation. The spontaneous echo contrast ('smoke') is a direct echocardiographic sign of blood stasis — red cell rouleaux formation and platelet aggregation occur when blood moves slowly through a large, poorly contracting chamber. This fulfills Virchow's triad (stasis + endothelial dysfunction from wall stretch + hypercoagulable state). While antithrombin III can be depleted in severe hepatic congestion, this is not the primary mechanism. The absence of a murmur despite severe LV dilation is a classic DCM finding — the ventricle dilates uniformly without mitral leaflet distortion initially.

Question 9: What is the metabolic basis for pregnancy toxemia (ketosis) in ewes?

Excess dietary carbohydrate causing rumen acidosis
Negative energy balance in late gestation causing mobilization of fat and accumulation of ketone bodies (Correct answer)
Primary hypocalcemia from fetal calcium demands
Hyperglycemia from insulin resistance

Correct answer: Negative energy balance in late gestation causing mobilization of fat and accumulation of ketone bodies

In late gestation with multiple fetuses, the ewe's energy demands exceed intake, forcing hepatic fat mobilization and ketogenesis that overwhelms clearance capacity.

Question 10: Neostigmine is administered to reverse neuromuscular blockade. Which agent should always be co-administered?

Flumazenil
Ondansetron
Epinephrine
Atropine or glycopyrrolate (Correct answer)

Correct answer: Atropine or glycopyrrolate

An anticholinergic (atropine or glycopyrrolate) must accompany neostigmine to counteract muscarinic side effects including bradycardia and bronchospasm.

Question 11: The anatomical position of the appendix is most commonly:

Paracolic
Subcecal
Pelvic (descending into true pelvis)
Retrocecal (Correct answer)

Correct answer: Retrocecal

In approximately 65% of individuals, the appendix lies in a retrocecal position, which can make the presentation of appendicitis atypical.

Question 12: During the avian respiratory cycle, in which phase does air flow through the parabronchi of the bird lung, and in which direction does blood flow relative to this airstream?

During both inspiration and expiration; blood flows parallel (concurrent) to airflow
During both inspiration and expiration; blood flows countercurrent (crosscurrent) to airflow (Correct answer)
During expiration only; blood flows in the same direction as airstream through the parabronchi
During inspiration only; blood flows countercurrent to airflow through the parabronchi

Correct answer: During both inspiration and expiration; blood flows countercurrent (crosscurrent) to airflow

Birds have a flow-through lung: fresh air passes through the parabronchi during BOTH inspiration (from caudal air sacs) and expiration (from cranial air sacs), providing unidirectional airflow. Blood in the parabronchial capillaries flows at right angles (crosscurrent) to the airstream, maximizing O2 extraction efficiency — allowing birds to maintain oxygenation at high altitudes where mammals would fail.

Question 13: A 7-year-old Quarter Horse mare presents with acute onset of profound weakness, muscle fasciculations, and dysphagia. Serum chemistry reveals markedly elevated CK and AST. EMG shows complex repetitive discharges and positive sharp waves. A muscle biopsy demonstrates vacuolar myopathy with periodic acid-Schiff (PAS)-positive inclusions. Which mutation is most likely responsible for this presentation?

RYR1 missense mutation causing sarcoplasmic reticulum calcium leak
GYS1 gain-of-function mutation causing glycogen synthase overactivity (Correct answer)
TRIM63 frameshift mutation causing impaired muscle protein ubiquitination
SCN4A loss-of-function mutation causing sodium channel inactivation failure

Correct answer: GYS1 gain-of-function mutation causing glycogen synthase overactivity

The PAS-positive vacuolar inclusions represent excessive glycogen accumulation, hallmark of Polysaccharide Storage Myopathy (PSSM) Type 1, caused by a gain-of-function mutation in GYS1 (glycogen synthase 1). This leads to constitutively active glycogen synthase, causing unbranched polysaccharide accumulation. RYR1 mutations cause Malignant Hyperthermia. SCN4A mutations underlie Hyperkalemic Periodic Paralysis. TRIM63 mutations are associated with human muscular atrophy, not equine PSSM.

Question 14: In a bitch with a closed-cervix pyometra, treatment with aglepristone (a progesterone receptor antagonist) is initiated. Which of the following best explains the mechanism by which aglepristone facilitates cervical opening in this condition?

Aglepristone competitively blocks myometrial progesterone receptors, causing uterine contractions that mechanically force cervical dilation
Aglepristone directly binds cervical smooth muscle glucocorticoid receptors, inducing nitric oxide synthase upregulation and smooth muscle relaxation
Progesterone receptor blockade removes the inhibition on estrogen-driven cervical collagen remodeling and relaxin-mediated softening, allowing cervicovaginal relaxation (Correct answer)
Blockade of progesterone receptors in the anterior pituitary triggers a compensatory LH surge that stimulates ovarian estradiol, causing cervical opening

Correct answer: Progesterone receptor blockade removes the inhibition on estrogen-driven cervical collagen remodeling and relaxin-mediated softening, allowing cervicovaginal relaxation

Progesterone normally keeps the cervix closed, firm, and impermeable by suppressing estrogen-driven collagen lysis and preventing prostaglandin E2-mediated softening. By competitively antagonizing progesterone receptors at the level of the cervix and uterus, aglepristone removes this inhibition, allowing the estrogen-dominant state and prostaglandin/relaxin pathways to soften and dilate the cervix — enabling drainage of the purulent uterine contents. The myometrial contraction effect (choice A) is a secondary benefit but is not the primary mechanism for cervical opening. Aglepristone does not act via glucocorticoid receptors or induce an LH surge.

Question 15: A dog repeatedly circles its kennel, vocalizes, and self-mutilates. These signs are most consistent with:

REM sleep disorder
Normal exploratory behavior
Hepatic encephalopathy
Stereotypic behavior from chronic stress (Correct answer)

Correct answer: Stereotypic behavior from chronic stress

Repetitive, invariant motor patterns (stereotypies) plus self-mutilation in a restricted environment indicate chronic psychological stress and compromised welfare.

Question 16: In a cadaveric dissection, the following structures are identified in the posterior mediastinum: the thoracic duct, azygos vein, and descending aorta. At the level of T8, which structure passes through the diaphragm at the caval hiatus?

Inferior vena cava and left phrenic nerve
Thoracic duct and azygos vein
Inferior vena cava and right phrenic nerve (Correct answer)
Inferior vena cava and vagus nerve

Correct answer: Inferior vena cava and right phrenic nerve

The caval hiatus in the diaphragm is located at T8 and transmits the inferior vena cava along with the right phrenic nerve. The aortic hiatus (T12) transmits the aorta, thoracic duct, and azygos vein. The esophageal hiatus (T10) transmits the esophagus and both vagus nerves. The right phrenic nerve passes through the caval opening rather than through the muscle itself because the IVC is intimately associated with the central tendon where the caval hiatus is located.

Question 17: A patient on chemotherapy develops peripheral neuropathy and the Vinca alkaloid vincristine is suspected. What is the mechanism of this toxicity?

Binding beta-tubulin and inhibiting microtubule polymerization (Correct answer)
Intercalating into DNA and blocking RNA synthesis
Alkylating DNA and preventing strand separation
Inhibiting topoisomerase II and causing double-strand breaks

Correct answer: Binding beta-tubulin and inhibiting microtubule polymerization

Vincristine binds beta-tubulin dimers and prevents microtubule assembly, disrupting axonal transport in peripheral neurons, which leads to sensorimotor neuropathy.

Question 18: On fluoroscopic cystourethrogram (VCUG), which finding is diagnostic of vesicoureteral reflux?

Bladder neck narrowing during voiding
Retrograde filling of contrast from the bladder into the ureter and renal pelvis (Correct answer)
Filling defect in the bladder lumen
Trabeculae of the bladder wall during filling

Correct answer: Retrograde filling of contrast from the bladder into the ureter and renal pelvis

VUR is diagnosed when contrast instilled into the bladder refluxes retrograde up the ureter and into the renal collecting system.

Question 19: Which first-line drug for type 2 diabetes primarily reduces hepatic glucose production?

Pioglitazone
Metformin (Correct answer)
Glipizide
Sitagliptin

Correct answer: Metformin

Metformin activates AMP-activated protein kinase (AMPK), suppressing hepatic gluconeogenesis and glycogenolysis, thereby reducing fasting plasma glucose without causing hypoglycemia.

Question 20: A 58-year-old man undergoes nephrectomy for a renal mass. Histology reveals tumor cells with abundant clear cytoplasm arranged in nests separated by a delicate vascular network. Immunohistochemistry shows positivity for CD10, vimentin, and carbonic anhydrase IX (CAIX), but negativity for CK7 and TFE3. A deletion in which chromosomal region is most characteristic of this tumor type?

Deletion of chromosome 11p13 (WT1 locus)
Translocation t(X;1)(p11;q21) involving TFE3
Deletion of chromosome 3p (VHL locus) (Correct answer)
Monosomy of chromosome 1

Correct answer: Deletion of chromosome 3p (VHL locus)

The described tumor is clear cell renal cell carcinoma (ccRCC), the most common renal malignancy. The characteristic molecular alteration is loss of heterozygosity at chromosome 3p25, where the VHL (von Hippel-Lindau) tumor suppressor gene resides. VHL inactivation leads to constitutive HIF activation and downstream upregrowth of VEGF and PDGF. CAIX positivity reflects HIF-driven transcription. TFE3 translocation at Xp11 characterizes Xp11 translocation RCC, a separate entity with TFE3 positivity. WT1 deletion is associated with Wilms tumor. Monosomy 1 is seen in chromophobe RCC along with monosomies of chromosomes 2, 6, 10, 13, and 17.

Question 21: Parvovirus type 2 in dogs primarily damages which tissue to cause hemorrhagic enteritis?

Duodenal Brunner's glands
Colonic goblet cells
Intestinal crypt epithelium (Correct answer)
Gastric parietal cells

Correct answer: Intestinal crypt epithelium

Canine parvovirus-2 targets rapidly dividing intestinal crypt epithelial cells, destroying the mucosal renewal mechanism and leading to hemorrhagic enteritis.

Question 22: A 45-year-old woman presents with episodic severe headaches, diaphoresis, and hypertension. Urine metanephrines are markedly elevated. Surgical resection of a right adrenal mass is performed. Histologically, the tumor shows a 'Zellballen' (nest) pattern with sustentacular cells at the periphery, and is positive for chromogranin A, synaptophysin, and S-100 (sustentacular cells). Which of the following histological features is the MOST reliable indicator of malignant behavior in this tumor?

Presence of capsular and vascular invasion with metastasis to non-chromaffin tissue (Correct answer)
Large cell size with prominent nucleoli and pleomorphic nuclei
High mitotic rate greater than 2 per 10 high-power fields
Tumor necrosis on gross and histologic examination

Correct answer: Presence of capsular and vascular invasion with metastasis to non-chromaffin tissue

Pheochromocytoma is notorious for being one of the few tumors where malignancy CANNOT be reliably determined by histological features alone — even capsular invasion, necrosis, high mitotic rate, and pleomorphism can be seen in benign lesions. The ONLY absolute criterion for malignancy in pheochromocytoma is the presence of metastasis to sites that normally lack chromaffin tissue (e.g., lymph nodes, liver, lung, bone). PASS (Pheochromocytoma of the Adrenal Gland Scaled Score) uses multiple histologic parameters, but none are individually definitive. This distinguishes pheochromocytoma from most other endocrine tumors and is a classic board-level concept.

Question 23: A researcher studying drug tolerance finds that prolonged morphine administration leads to receptor desensitization. Which intracellular event is MOST directly responsible for the rapid (minutes-to-hours) phase of μ-opioid receptor desensitization?

Upregulation of adenylyl cyclase isoforms leading to cAMP superactivation
Internalization of the receptor via clathrin-independent lipid raft pathways
Downregulation of receptor mRNA transcription via CREB suppression
GRK-mediated phosphorylation of the receptor C-terminal tail promoting β-arrestin recruitment (Correct answer)

Correct answer: GRK-mediated phosphorylation of the receptor C-terminal tail promoting β-arrestin recruitment

The rapid phase of μ-opioid receptor (MOR) desensitization is initiated by G protein-coupled receptor kinases (GRKs), particularly GRK2/3, which phosphorylate serine/threonine residues on the receptor's intracellular C-terminal tail. This phosphorylation recruits β-arrestin, which sterically uncouples the receptor from its Gi/Go protein and simultaneously triggers clathrin-mediated internalization. cAMP superactivation (adenylyl cyclase upregulation) is a longer-term compensatory mechanism underlying aspects of physical dependence, not the rapid desensitization phase.

Question 24: A newborn presents with cataracts, jaundice, and E. coli sepsis within the first week of life. Which metabolic disorder is most likely?

Glycogen storage disease type I
Galactosemia (Correct answer)
Fructosemia
Maple syrup urine disease

Correct answer: Galactosemia

Classic galactosemia (GALT deficiency) causes accumulation of galactose-1-phosphate leading to cataracts, liver disease, and predisposition to E. coli neonatal sepsis.

Question 25: A 6-month-old heifer born co-twin to a bull presents with a shallow vaginal vault (4 cm depth) and no history of observed estrous cycles. Physical examination is otherwise unremarkable. Which diagnostic test provides the MOST definitive confirmation of freemartinism?

Rectal palpation confirming bilateral uterine horn hypoplasia and absent palpable ovarian structures
Karyotyping of peripheral blood lymphocytes demonstrating XX/XY chimerism (Correct answer)
Serial progesterone assays 14 days apart showing persistently low values (<1 ng/mL)
Serum anti-Müllerian hormone (AMH) measurement demonstrating elevation above the normal heifer reference range

Correct answer: Karyotyping of peripheral blood lymphocytes demonstrating XX/XY chimerism

Karyotyping revealing XX/XY chimerism in peripheral blood lymphocytes is the definitive test for freemartinism. Placental vascular anastomoses between heterosexual twins allow bidirectional exchange of hematopoietic progenitor cells, creating persistent blood chimerism detectable throughout the animal's life. AMH may be elevated due to residual gonadal tissue but is not pathognomonic. Low progesterone and clinical findings (shallow vagina, uterine hypoplasia) are consistent but not specific — other causes of sexual infantilism exist and would require different management.

Question 26: During a cadaveric dissection of the hand, a student notes that a small muscle originates from the hook of the hamate and the flexor retinaculum, and inserts into the medial border of the fifth metacarpal. Paralysis of this muscle would most impair which movement?

Abduction of the little finger (Correct answer)
Flexion of the little finger at the MCP joint
Opposition of the little finger
Adduction of the little finger

Correct answer: Abduction of the little finger

The muscle described — originating from the hook of the hamate and flexor retinaculum and inserting into the medial border of the fifth metacarpal — is the abductor digiti minimi. It is the prime mover for little finger abduction at the MCP joint. The opponens digiti minimi (also from the hamate) inserts along the shaft of the fifth metacarpal to produce opposition. Flexor digiti minimi brevis flexes the proximal phalanx. Adduction is produced by the palmar interossei.

Question 27: In the fasted state, the liver preferentially produces which ketone body as the primary export fuel for the brain?

Acetoacetate
Beta-hydroxybutyrate (Correct answer)
Malonyl-CoA
Acetone

Correct answer: Beta-hydroxybutyrate

Beta-hydroxybutyrate is the predominant ketone body exported by the liver during prolonged fasting and is the major alternative fuel for the brain.

Question 28: Feline infectious peritonitis (FIP) is caused by a mutated form of which virus?

Feline calicivirus
Feline enteric coronavirus (Correct answer)
Feline herpesvirus-1
Feline leukemia virus

Correct answer: Feline enteric coronavirus

FIP arises when feline enteric coronavirus mutates to a highly pathogenic biotype that infects and replicates within macrophages, causing systemic vasculitis.

Question 29: Which nerve is at greatest risk of injury during a perineal urethrostomy in a male cat?

Femoral nerve
Sciatic nerve
Pudendal nerve (Correct answer)
Obturator nerve

Correct answer: Pudendal nerve

The pudendal nerve supplies the perineal region and urethra and is in close proximity to the surgical field during perineal urethrostomy.

Question 30: Ultrasound of the liver reveals a 3 cm lesion with posterior acoustic enhancement and uniform anechoic internal echogenicity. Contrast-enhanced CT shows peripheral nodular enhancement in the arterial phase that fills in centripetally on delayed imaging. This enhancement pattern is MOST characteristic of:

Focal nodular hyperplasia with central scar and spoke-wheel vascularity
Hepatic adenoma with heterogeneous enhancement and intralesional fat
Hepatocellular carcinoma with arterial hypervascularity and washout
Cavernous hemangioma with progressive centripetal fill-in (Correct answer)

Correct answer: Cavernous hemangioma with progressive centripetal fill-in

Cavernous hemangiomas classically demonstrate peripheral nodular enhancement in the arterial phase with progressive centripetal fill-in on delayed images, reflecting slow blood pooling in large vascular spaces. On ultrasound, they appear uniformly hyperechoic (in fatty livers) or anechoic with posterior acoustic enhancement. HCC shows arterial enhancement with venous phase washout. FNH has a central scar and spoke-wheel pattern. Adenoma shows heterogeneous enhancement, often with fat or hemorrhage.

Question 31: An 18-year-old pony is presented with hirsutism, laminitis, and polyuria/polydipsia. Pituitary Pars Intermedia Dysfunction (PPID) is suspected. Which of the following is considered the most reliable and safe first-line diagnostic test for PPID, especially in early or equivocal cases?

Thyrotropin-releasing hormone (TRH) stimulation test measuring ACTH (Correct answer)
Baseline cortisol concentration
Dexamethasone suppression test (DST)
Combined glucose-insulin tolerance test

Correct answer: Thyrotropin-releasing hormone (TRH) stimulation test measuring ACTH

The thyrotropin-releasing hormone (TRH) stimulation test, which measures the ACTH response to TRH administration, is considered a highly sensitive test for diagnosing PPID, particularly in early stages. It is generally preferred over the dexamethasone suppression test (DST) due to concerns that administering corticosteroids in the DST could potentially exacerbate or induce laminitis in at-risk animals. Baseline cortisol is unreliable due to normal fluctuations.

Question 32: A 70-year-old man is found to have a left renal mass on CT. Microscopically the tumor shows clear cells with abundant lipid and glycogen. What is the most likely diagnosis?

Oncocytoma
Transitional cell carcinoma
Clear cell renal cell carcinoma (Correct answer)
Wilms tumor

Correct answer: Clear cell renal cell carcinoma

Clear cell renal cell carcinoma is the most common renal malignancy in adults and shows characteristic clear cytoplasm due to lipid and glycogen accumulation.

Question 33: On CT of the chest, a 'crazy paving' pattern (ground-glass opacity with superimposed interlobular septal thickening) is classically associated with which condition?

Pulmonary alveolar proteinosis (Correct answer)
Usual interstitial pneumonia
Lymphangitic carcinomatosis
Sarcoidosis

Correct answer: Pulmonary alveolar proteinosis

Crazy paving is the classic CT pattern of pulmonary alveolar proteinosis, caused by lipoproteinaceous material filling alveolar spaces.

Question 34: Which of the following Plasmodium-like protozoa infects cattle erythrocytes, is transmitted by Ixodes ticks, and can cause severe hemolytic anemia in splenectomized animals?

Babesia bovis (Correct answer)
Anaplasma marginale
Trypanosoma brucei
Theileria parva

Correct answer: Babesia bovis

Babesia bovis is an intraerythrocytic protozoan transmitted by Rhipicephalus (Boophilus) microplus ticks that causes bovine babesiosis (redwater fever). Splenectomized animals are especially vulnerable because the spleen normally removes parasitized red cells. Theileria infects lymphocytes first, Trypanosoma is flagellated and extracellular, and Anaplasma is a rickettsial organism, not a protozoan.

Question 35: A routine urinalysis is performed on a dog with a suspected urinary tract infection. The microscopic examination of the urine sediment reveals numerous rod-shaped bacteria, more than 10 white blood cells per high-power field, and many struvite crystals. Which of the following is a common consequence of this type of infection?

The formation of calcium oxalate crystals will be promoted.
The urine pH will become more alkaline. (Correct answer)
The urine pH will become more acidic.
The urine specific gravity will be fixed at 1.010.

Correct answer: The urine pH will become more alkaline.

Struvite (magnesium ammonium phosphate) crystals tend to form in alkaline urine. Many common urinary tract infections in dogs are caused by urease-producing bacteria (e.g., Staphylococcus, Proteus). These bacteria break down urea into ammonia, which raises the urine pH (makes it more alkaline), promoting the precipitation of struvite crystals and potentially leading to stone formation.

Question 36: The femoral triangle contains all of the following EXCEPT:

Femoral artery
Femoral nerve
Obturator nerve (Correct answer)
Femoral vein

Correct answer: Obturator nerve

The femoral triangle contains the femoral nerve, artery, and vein (lateral to medial: nerve, artery, vein); the obturator nerve exits through the obturator foramen medially.

Question 37: On flow cytometry of a bone marrow aspirate, a population of cells is identified that is CD19+, CD5+, CD23+, CD20 dim, surface IgM dim, and FMC7−. The Matutes score is 4. A FISH panel reveals del(17p) and del(11q). Which prognostic statement is MOST accurate regarding this patient's disease course?

The combination of del(17p) and del(11q) is associated with the best overall survival in CLL
Del(17p) alone confers a favorable prognosis with standard chemoimmunotherapy
Del(17p) indicates TP53 dysfunction and poor response to most conventional therapies (Correct answer)
Del(11q) predicts excellent response to alkylating agents as monotherapy

Correct answer: Del(17p) indicates TP53 dysfunction and poor response to most conventional therapies

Del(17p) disrupts TP53 and is the most adverse cytogenetic abnormality in CLL, conferring resistance to purine analogues and alkylating agents. These patients have the shortest time to treatment and overall survival. Del(11q) (ATM loss) is also high-risk but responds better to bendamustine-based regimens. BTK inhibitors (ibrutinib) are now preferred for del(17p) CLL. The combination of both deletions is not a favorable prognostic pairing.

Question 38: The direct pupillary light reflex (PLR) assesses integrity of which anatomical pathway?

Trigeminal nerve → ciliary ganglion → pupillary sphincter
Retina → lateral geniculate nucleus → occipital cortex → sympathetic trunk → iris dilator
Optic nerve → visual cortex → oculomotor nucleus → ciliary ganglion → pupillary sphincter
Optic nerve → pretectal nucleus → bilateral Edinger-Westphal nucleus → ciliary ganglion → pupillary sphincter (Correct answer)

Correct answer: Optic nerve → pretectal nucleus → bilateral Edinger-Westphal nucleus → ciliary ganglion → pupillary sphincter

The PLR pathway does NOT require cortical processing. Afferent signal travels via the optic nerve (CN II) → optic chiasm → pretectal nucleus (midbrain) → bilateral Edinger-Westphal (parasympathetic) nuclei → oculomotor nerve (CN III) → ciliary ganglion → short ciliary nerves → pupillary sphincter muscle. The bilateral projection from the pretectal nucleus explains the consensual (indirect) PLR. Lesions in the visual cortex do not abolish the PLR.

Question 39: A 6-month-old dog presents with small-stature, hepatic encephalopathy, and low BUN. A post-prandial bile acid test shows markedly elevated 2-hour values. What is the most likely diagnosis?

Congenital portosystemic shunt (Correct answer)
Microvascular dysplasia
Glycogen storage disease
Copper storage hepatopathy

Correct answer: Congenital portosystemic shunt

A congenital portosystemic shunt causes decreased hepatic perfusion, low BUN and albumin, and dramatically elevated post-prandial bile acids in young dogs.

Question 40: During a necropsy of a sheep flock with increased abortion rates, placentomes show intercotyledonary edema and leathery discoloration. Chlamydia abortus (formerly Chlamydophila abortus) is confirmed by PCR. Which of the following statements most accurately distinguishes C. abortus from Coxiella burnetii in this epidemiological context?

C. abortus replicates within phagolysosomes using similar acid-activation mechanisms as C. burnetii
C. abortus forms a spore-like small cell variant enabling extended environmental survival comparable to C. burnetii
C. abortus poses greater zoonotic risk via the respiratory route than C. burnetii in farm workers near lambing sheds
C. abortus is transmitted primarily via direct contact with infected aborted material, while C. burnetii is predominantly transmitted via aerosol from contaminated parturient fluids (Correct answer)

Correct answer: C. abortus is transmitted primarily via direct contact with infected aborted material, while C. burnetii is predominantly transmitted via aerosol from contaminated parturient fluids

C. abortus is transmitted primarily through direct contact with infected aborted fetuses, placentas, and uterine discharges, with limited aerosol transmission. In contrast, C. burnetii is extraordinarily resistant in its spore-like small cell variant form and is predominantly transmitted via aerosol, making it a far greater zoonotic aerosol hazard. C. burnetii also replicates in phagolysosomes using acid-activation; C. abortus replicates in inclusions that intercept the exocytic pathway and avoids lysosomal fusion.

Question 41: Giardia duodenalis trophozoites are best characterized by which morphological feature on a fecal smear?

Two nuclei and a ventral adhesive disc giving a 'falling leaf' motility (Correct answer)
Axostyle protruding from a single anterior nucleus
Single nucleus and undulating membrane
Four nuclei arranged symmetrically in a cyst wall

Correct answer: Two nuclei and a ventral adhesive disc giving a 'falling leaf' motility

Giardia trophozoites are binucleate, pear-shaped flagellates with a concave ventral adhesive disc used to attach to intestinal epithelium. Their characteristic 'falling leaf' tumbling motility is seen in fresh wet mounts. Cysts (not trophozoites) contain 4 nuclei. Tritrichomonas has an undulating membrane and single nucleus. Axostyle prominence is a feature of Trichomonas.

Question 42: A patient presents with weakness of shoulder abduction beyond 90° and difficulty with overhead activities. Imaging reveals compression at the spinoglenoid notch. Which specific branch of which nerve is most likely affected?

Deep branch of the suprascapular nerve (Correct answer)
Posterior cord terminal branch of the radial nerve
Inferior branch of the suprascapular nerve
Anterior branch of the axillary nerve

Correct answer: Deep branch of the suprascapular nerve

The suprascapular nerve passes through the suprascapular notch to innervate the supraspinatus, then wraps around the spine of the scapula at the spinoglenoid notch to innervate the infraspinatus. Compression at the spinoglenoid notch specifically affects the infraspinatus branch (deep branch), causing isolated infraspinatus weakness. Since the infraspinatus is critical for external rotation and assists in abduction beyond 90°, this results in the described deficit without affecting supraspinatus function.

Question 43: Which local anesthetic is MOST associated with cardiovascular toxicity due to its high lipid solubility and slow sodium channel dissociation?

Chloroprocaine
Bupivacaine (Correct answer)
Lidocaine
Mepivacaine

Correct answer: Bupivacaine

Bupivacaine has high lipid solubility and slow dissociation from cardiac sodium channels, making ventricular arrhythmias difficult to resuscitate.

Question 44: Which regulatory body in the US directly oversees the Animal Welfare Act compliance for research institutions?

FDA Center for Veterinary Medicine
NIH Office of Laboratory Animal Welfare
USDA APHIS Animal Care (Correct answer)
CDC Office of Safety, Security, and Asset Management

Correct answer: USDA APHIS Animal Care

USDA APHIS Animal Care conducts inspections and enforces AWA regulations at research facilities, zoos, and other covered establishments.

Question 45: Which trace mineral deficiency in cattle causes 'falling disease' (sudden cardiac failure) and depigmentation of the hair coat?

Copper deficiency (Correct answer)
Iodine deficiency
Zinc deficiency
Selenium deficiency

Correct answer: Copper deficiency

Copper deficiency impairs cytochrome c oxidase in cardiac muscle (causing heart failure) and tyrosinase activity (causing hair depigmentation and sunbleached coat).

Question 46: Which of the following dietary modifications is most effective in preventing obstructive urolithiasis in male small ruminants, particularly those on high-concentrate diets?

Supplementing with high levels of magnesium
Feeding a diet high in protein to increase water intake
Increasing the dietary calcium-to-phosphorus ratio to at least 2:1 (Correct answer)
Adding sodium bicarbonate to the feed

Correct answer: Increasing the dietary calcium-to-phosphorus ratio to at least 2:1

High-concentrate (grain) diets are often high in phosphorus and low in calcium, which predisposes to the formation of phosphatic (struvite) calculi. Ensuring the dietary calcium-to-phosphorus ratio is at least 2:1 helps prevent the formation of these stones by reducing the amount of phosphorus absorbed and excreted in the urine.

Question 47: A kidney biopsy immunofluorescence shows linear IgG deposits along the glomerular basement membrane. This pattern is most consistent with which disease?

IgA nephropathy
Lupus nephritis
Membranous nephropathy
Goodpasture syndrome (Correct answer)

Correct answer: Goodpasture syndrome

Linear IgG along the GBM is the hallmark of anti-GBM disease (Goodpasture syndrome), reflecting antibodies directed against the GBM itself.

Question 48: On MRI of the knee, a 'bucket-handle' tear of the meniscus is best recognized by which imaging feature?

A displaced fragment within the intercondylar notch creating a 'double PCL sign' (Correct answer)
Increased T2 signal at the meniscal root
Complete absence of the meniscus on coronal imaging
Vertical cleavage on sagittal T2 imaging

Correct answer: A displaced fragment within the intercondylar notch creating a 'double PCL sign'

A bucket-handle tear displaces the inner fragment into the intercondylar notch, producing a double PCL sign on sagittal MRI.

Question 49: Autopsy of a 72-year-old woman with a history of longstanding systemic lupus erythematosus reveals sterile verrucous endocarditis affecting both surfaces of the mitral valve leaflets. Which of the following best characterizes the pathogenesis of this finding?

Bacteremic seeding of a previously damaged valve from remote skin infection
Immune complex deposition and antiphospholipid antibody-mediated microthrombosis on valve surfaces (Correct answer)
Turbulent blood flow across a myxomatous valve leading to platelet aggregation
Direct viral cytopathic injury to valvular endothelial cells causing sterile vegetations

Correct answer: Immune complex deposition and antiphospholipid antibody-mediated microthrombosis on valve surfaces

Libman-Sacks endocarditis, the sterile verrucous endocarditis of SLE, is pathognomonic for this condition and uniquely affects both surfaces (atrial AND ventricular) of the mitral valve leaflets — unlike rheumatic fever vegetations which are limited to the line of closure. The mechanism involves immune complex deposition and antiphospholipid antibodies (which cause microthrombosis) producing small, irregular, warty vegetations. These can embolize but are not infective. Myxomatous degeneration (mitral valve prolapse) leads to regurgitation and late risk of infective endocarditis, not Libman-Sacks lesions. Viral valvulitis is not a recognized mechanism.

Question 50: A 6-year-old intact male cat undergoes perineal urethrostomy. Two weeks postoperatively the owner reports urine scalding and a narrow urinary stream. Retrograde urethrogram reveals a focal stricture at the anastomotic site. Which suture technique error during the original procedure is MOST likely responsible?

Use of rapidly absorbable suture material (poliglecaprone 25) rather than polyglycolic acid
Excessive tension on interrupted sutures placed too close to the urethral mucosa edge, causing ischemic necrosis (Correct answer)
Placement of too few sutures, allowing mucosal eversion and urothelial exposure
Failure to spatulate the urethral opening prior to anastomosis

Correct answer: Excessive tension on interrupted sutures placed too close to the urethral mucosa edge, causing ischemic necrosis

Stricture formation at a perineal urethrostomy is classically caused by ischemic necrosis from sutures placed under excessive tension or too close to the delicate urethral mucosal edge, interrupting the marginal blood supply. This leads to fibrosis and luminal narrowing. While spatulation is important in ureteral anastomoses, PU technique relies on precise mucosal apposition. Poliglecaprone 25 is actually appropriate for this procedure; the issue is technique, not material choice.

Question 51: Equine infectious anemia (EIA) is diagnosed using which regulatory test in the United States?

PCR for EIA proviral DNA
ELISA for viral capsid antigen
Coggins test (agar gel immunodiffusion) (Correct answer)
Virus neutralization test

Correct answer: Coggins test (agar gel immunodiffusion)

The Coggins test (agar gel immunodiffusion for antibodies to EIA p26 antigen) is the official USDA-recognized test for regulatory purposes including interstate movement.

Question 52: In ruminants, which forestomach compartment is responsible for receiving ingesta directly from the esophagus and initiating fermentation?

Reticulum
Omasum
Abomasum
Rumen (Correct answer)

Correct answer: Rumen

The rumen is the largest forestomach compartment and is the primary site of microbial fermentation of plant material in ruminants.

Question 53: What is the effect of hyperventilation on cerebral blood flow during neuroanesthesia?

No effect on CBF
Decreases CBF by causing cerebral vasoconstriction via hypocapnia (Correct answer)
Increases CBF by raising intracranial pressure
Increases CBF by dilating cerebral vasculature

Correct answer: Decreases CBF by causing cerebral vasoconstriction via hypocapnia

Hypocapnia from hyperventilation causes cerebral vasoconstriction, reducing cerebral blood flow and intracranial pressure.

Question 54: The zoonotic bacterium Francisella tularensis is most commonly transmitted to humans through which route?

Fecal-oral contamination from cattle
Ingestion of undercooked pork
Inhalation of bat guano
Arthropod bites (ticks, deer flies) or contact with infected rabbit tissues (Correct answer)

Correct answer: Arthropod bites (ticks, deer flies) or contact with infected rabbit tissues

Tularemia is primarily transmitted via tick or deer fly bites or direct contact with infected lagomorphs, especially rabbits during hunting season.

Question 55: In the male dog, the bulbus glandis engorges during copulation to create a 'tie' with the female. Which erectile tissue type composes the bulbus glandis, and how does it differ from the corpus cavernosum penis in terms of venous drainage control?

The bulbus glandis is a distinct erectile structure composed of sinusoidal erectile tissue not homologous to either corpus cavernosum or corpus spongiosum, maintained by arteriovenous shunt closure
The bulbus glandis is composed of corpus spongiosum tissue with a prominent tunica albuginea; venous drainage is occluded by contraction of the bulbospongiosus muscle compressing emissary veins (Correct answer)
The bulbus glandis is composed of corpus cavernosum tissue with a thick tunica albuginea that traps blood via veno-occlusion, identical to the mechanism in the corpus cavernosum penis
The bulbus glandis is composed of corpus spongiosum tissue and lacks a tunica albuginea, relying on ischiocavernosus muscle compression rather than trabecular veno-occlusion for engorgement

Correct answer: The bulbus glandis is composed of corpus spongiosum tissue with a prominent tunica albuginea; venous drainage is occluded by contraction of the bulbospongiosus muscle compressing emissary veins

The bulbus glandis is an expansion of the corpus spongiosum (pars longa glandis surrounds the urethra, while the bulbus glandis flanks it proximally). Unlike the corpus cavernosum penis (which has a rigid tunica albuginea enabling high-pressure erection), the bulbus glandis has its own tunica and depends primarily on bulbospongiosus muscle activity compressing emissary veins to maintain engorgement. This sustained muscular compression is what makes the copulatory tie functionally possible for 15–30 minutes.

Question 56: Intraoperatively, a patient develops masseter muscle rigidity after succinylcholine administration. Core temperature is 37.2°C and the patient is hemodynamically stable. Which action is MOST appropriate at this time?

Proceed cautiously — masseter spasm alone is physiologic and requires only observation
Administer dantrolene 2.5 mg/kg immediately and cancel the case
Discontinue all triggering agents, monitor creatine kinase, lactate, and temperature closely, and have dantrolene immediately available (Correct answer)
Switch to a non-depolarizing agent and complete the case under total intravenous anesthesia without further intervention

Correct answer: Discontinue all triggering agents, monitor creatine kinase, lactate, and temperature closely, and have dantrolene immediately available

Isolated masseter muscle rigidity (MMR) after succinylcholine is considered a forme fruste or harbinger of malignant hyperthermia (MH) susceptibility in a significant proportion of cases — estimates range from 15–50%. The current evidence-based approach is to discontinue volatile agents and succinylcholine, convert to TIVA if the case must continue, monitor continuously for MH signs (rising EtCO₂, temperature, acidosis, myoglobinuria), and have dantrolene immediately at bedside. Prophylactic dantrolene without MH signs is not mandatory but must be available. Simply observing (B) underestimates risk; proceeding with TIVA without vigilance (D) ignores the ongoing MH risk window.

Question 57: On a barium swallow study, a 'bird-beak' appearance at the gastroesophageal junction is characteristic of which condition?

Achalasia (Correct answer)
Diffuse esophageal spasm
Esophageal carcinoma
Zenker's diverticulum

Correct answer: Achalasia

Achalasia causes failure of LES relaxation, producing a smooth tapered narrowing at the GEJ resembling a bird's beak on barium swallow.

Question 58: What is the primary cause of freemartinism in cattle?

Chromosomal trisomy in the female twin
Nutritional deficiency during gestation
Infection with Brucella abortus in utero
Vascular anastomosis between twins of opposite sex sharing testosterone (Correct answer)

Correct answer: Vascular anastomosis between twins of opposite sex sharing testosterone

Freemartinism results from placental vascular anastomoses between male and female twins, allowing testosterone and anti-Müllerian hormone from the male to masculinize the female co-twin.

Question 59: A horse presents with mucopurulent nasal discharge and submandibular lymphadenopathy. Culture yields a beta-hemolytic Streptococcus with a Lancefield group C antigen. What is the most likely diagnosis?

Strangles caused by Streptococcus equi subsp. zooepidemicus
Pneumonia caused by Streptococcus pneumoniae
Strangles caused by Streptococcus equi subsp. equi (Correct answer)
Pigeon fever caused by Corynebacterium pseudotuberculosis

Correct answer: Strangles caused by Streptococcus equi subsp. equi

Streptococcus equi subsp. equi (group C Streptococcus) is the obligate pathogen causing classic strangles with abscessation of submandibular lymph nodes in horses.

Question 60: Body condition scoring (BCS) in dogs uses which scale and what score indicates ideal body condition?

1–10 scale; a score of 5–6 indicates ideal condition
1–5 scale; a score of 3 indicates ideal condition
1–9 scale; a score of 7–8 indicates ideal condition
1–9 scale; a score of 4–5 indicates ideal condition (Correct answer)

Correct answer: 1–9 scale; a score of 4–5 indicates ideal condition

The Purina/WSAVA 9-point BCS system for dogs rates 4–5 as ideal, where ribs are easily palpable with minimal fat cover and a waist is visible.

Question 61: In the polymerase chain reaction (PCR), what is the purpose of the denaturation step?

To extend the new DNA strand from the 3' end of each primer
To activate Taq polymerase by heat
To separate the double-stranded DNA template into single strands (Correct answer)
To allow primers to anneal to single-stranded template

Correct answer: To separate the double-stranded DNA template into single strands

Denaturation (typically 94–98°C) breaks the hydrogen bonds between complementary DNA strands, converting double-stranded DNA to single-stranded templates. This must precede primer annealing. Primer annealing occurs in the next step (lower temperature). Extension by Taq polymerase occurs at ~72°C. Taq is thermostable and does not require activation by heat.

Question 62: Which cell type in the gastric mucosa of dogs and cats secretes hydrochloric acid?

Chief (zymogenic) cells
Parietal (oxyntic) cells (Correct answer)
G cells
Mucous neck cells

Correct answer: Parietal (oxyntic) cells

Parietal (oxyntic) cells secrete hydrochloric acid via H+/K+-ATPase pumps, creating the highly acidic gastric environment needed for protein digestion.

Question 63: A 7-year-old Angus cow, 6 months pregnant, presents with bilateral papular lesions on the muzzle, nares, and oral mucosa, along with high fever (41.5°C), profuse salivation, and nasal discharge. Several herdmates are similarly affected. PCR of nasal swabs is positive for bovine herpesvirus-1 (BHV-1), but lesions are unusually severe. Which co-infecting pathogen is MOST likely responsible for the increased severity and the erosive oral lesions?

Mannheimia haemolytica
Bluetongue virus serotype 8
Mycoplasma bovis
Bovine viral diarrhea virus (BVDV) (Correct answer)

Correct answer: Bovine viral diarrhea virus (BVDV)

BHV-1 (IBR virus) typically causes rhinotracheitis with nasal and conjunctival lesions but rarely produces severe erosive oral mucosal lesions on its own. Co-infection with BVDV — particularly in a naïve or PI (persistently infected) herd — markedly potentiates mucosal disease severity and produces the erosive oral lesions characteristic of mucosal disease. BVDV also causes immunosuppression, worsening BHV-1 severity. Mannheimia haemolytica is a secondary bacterial pathogen causing pneumonia, not oral erosions. Mycoplasma bovis causes arthritis and pneumonia. Bluetongue virus causes oral erosions but through a different pathogenesis and vector (Culicoides) — the PCR positivity for BHV-1 and herd outbreak pattern point to a viral co-infection rather than bluetongue.

Question 64: Which of the following suture materials has the LONGEST retention of tensile strength, making it suitable for closure of body wall in large-breed dogs?

Polyglactin 910 (Vicryl)
Polydioxanone (PDS) (Correct answer)
Plain catgut
Poliglecaprone 25 (Monocryl)

Correct answer: Polydioxanone (PDS)

Polydioxanone (PDS) retains approximately 70% of its tensile strength at 2 weeks and 50% at 4 weeks, making it ideal for slowly healing tissues such as the linea alba.

Question 65: A 40-year-old with history of ulcerative colitis undergoes colectomy. The specimen shows dysplastic crypts with complex back-to-back glands and nuclear stratification confined to the mucosa. What is the most appropriate diagnosis?

Adenocarcinoma
High-grade dysplasia (Correct answer)
Low-grade dysplasia
Reactive atypia

Correct answer: High-grade dysplasia

High-grade dysplasia in inflammatory bowel disease is characterized by complex architectural distortion and marked nuclear atypia without invasion through the muscularis mucosae.

Question 66: A 7-year-old intact female Rottweiler presents with polyuria, polydipsia, and a purulent vaginal discharge. CBC reveals a leukocytosis of 42,000 cells/µL with a left shift. Abdominal radiographs show a markedly distended uterus. After emergency ovariohysterectomy and 48 hours of IV antibiotics, the dog develops persistent oliguria despite aggressive fluid therapy. Urine specific gravity is 1.010 and urine sodium is 68 mEq/L. What is the most likely cause of the persistent oliguria?

Renal medullary washout from chronic polyuria
Acute tubular necrosis secondary to sepsis-induced renal ischemia (Correct answer)
Glomerulonephritis from immune complex deposition
Pre-renal azotemia from inadequate fluid resuscitation

Correct answer: Acute tubular necrosis secondary to sepsis-induced renal ischemia

The combination of isosthenuria (USG 1.010), high urine sodium (>40 mEq/L indicating tubular dysfunction — normal tubules would reabsorb sodium), oliguria despite aggressive fluid therapy, and a septic history is classic for acute tubular necrosis (ATN). Sepsis causes renal ischemia via decreased cardiac output, microvascular thrombi, and inflammatory mediator release. Pre-renal azotemia would show urine sodium <20 mEq/L and respond to fluids. Glomerulonephritis typically causes proteinuria rather than oliguria acutely. Medullary washout would not explain oliguria or elevated urine sodium.

Question 67: The celiac trunk is the first unpaired branch of the abdominal aorta and typically divides into which three branches?

Superior mesenteric, inferior mesenteric, splenic arteries
Left gastric, splenic, common hepatic arteries (Correct answer)
Hepatic, gastroduodenal, right gastric arteries
Left gastric, right gastric, gastroduodenal arteries

Correct answer: Left gastric, splenic, common hepatic arteries

The celiac trunk classically trifurcates into the left gastric artery, splenic artery, and common hepatic artery.

Question 68: On an abdominal X-ray, 'thumbprinting' of the colon wall is most associated with which condition?

Irritable bowel syndrome
Diverticulosis
Colon polyps
Ischemic colitis (Correct answer)

Correct answer: Ischemic colitis

Thumbprinting represents submucosal edema and hemorrhage causing nodular indentations of the bowel wall, classic for ischemic colitis.

Question 69: During a splenectomy, which vessel must be carefully identified and ligated to avoid inadvertent injury to the pancreas?

Short gastric vessels and left gastroepiploic artery near the splenic hilus (Correct answer)
Right gastroepiploic artery
Celiac artery
Left gastric artery

Correct answer: Short gastric vessels and left gastroepiploic artery near the splenic hilus

The short gastric vessels and left gastroepiploic artery run near the splenic hilus in close proximity to the pancreatic tail, requiring careful dissection to avoid pancreatitis.

Question 70: Dermatophilosis in cattle and horses is caused by Dermatophilus congolensis. What is the correct classification of this organism?

Dimorphic fungus
Obligate intracellular bacterium
Gram-negative spirochete
Filamentous Gram-positive actinomycete (Correct answer)

Correct answer: Filamentous Gram-positive actinomycete

Dermatophilus congolensis is a Gram-positive, non-acid-fast filamentous actinomycete that produces motile zoospores and causes 'rain rot' or streptothricosis.

Question 71: A 10-year-old cat with chronic kidney disease stage 3 (IRIS) is started on phosphate restriction. Serum phosphorus remains elevated. Which phosphate binder is preferred in cats due to palatability and safety?

Sevelamer hydrochloride
Lanthanum carbonate
Aluminum hydroxide
Calcium carbonate (Correct answer)

Correct answer: Calcium carbonate

Calcium carbonate is commonly used in cats as a phosphate binder; it is palatable and effective, though dose titration is needed to avoid hypercalcemia.

Question 72: Which clinical sign is pathognomonic for tetanus in horses?

Flaccid paralysis of the hindlimbs
Trismus (lockjaw) with erect ears and tail elevation (Correct answer)
Hypersalivation with dysphagia only
Intermittent opisthotonus without muscle rigidity

Correct answer: Trismus (lockjaw) with erect ears and tail elevation

The combination of trismus, risus sardonicus (facial muscle contraction), erect ears, tail elevation, and generalized extensor rigidity triggered by stimuli is pathognomonic for tetanus.

Question 73: On MRI of the brain, periventricular white matter T2/FLAIR hyperintensities perpendicular to the corpus callosum ('Dawson's fingers') are characteristic of which condition?

Watershed infarcts
Multiple sclerosis (Correct answer)
Progressive multifocal leukoencephalopathy
Hypertensive small vessel disease

Correct answer: Multiple sclerosis

Dawson's fingers are ovoid MS plaques oriented along perivenular drainage pathways perpendicular to the ventricles, a hallmark of MS on MRI.

Question 74: Which of the following best describes the appropriate use of electrocautery in the monopolar mode?

Current is confined to the tip of the instrument only
It is safe to use near implanted pacemakers
Current flows between two handheld electrodes
Current passes from the active electrode through the patient to a grounding pad (Correct answer)

Correct answer: Current passes from the active electrode through the patient to a grounding pad

In monopolar electrosurgery, electrical current flows from the active electrode through the patient's tissues and returns via a dispersive grounding pad placed on the patient.

Question 75: The Apgar score assesses newborn status at 1 and 5 minutes after birth using which five criteria?

Activity, Pulse, Grimace, Appearance, Respiration (Correct answer)
Alertness, Pupil response, Grip, Auditory response, Reflexes
Arousal, Perfusion, Gastrointestinal function, Ambulation, Respiratory rate
Acrocyanosis, Pulse, Grunting, Axial tone, Reflexes

Correct answer: Activity, Pulse, Grimace, Appearance, Respiration

The Apgar score uses Activity (muscle tone), Pulse, Grimace (reflex irritability), Appearance (color), and Respiration, scored 0-2 each.

Question 76: A 55-year-old male presents to the emergency department with altered mental status, visual disturbances, and severe metabolic acidosis with an elevated anion gap. History from a family member suggests he may have ingested windshield wiper fluid. Which of the following is the most appropriate initial antidote?

Naloxone
Sodium Bicarbonate
Fomepizole (Correct answer)
Acetylcysteine

Correct answer: Fomepizole

The patient's symptoms are classic for methanol poisoning, a primary component of windshield wiper fluid. Methanol is metabolized by alcohol dehydrogenase to toxic metabolites like formic acid, which causes metabolic acidosis and optic nerve damage. Fomepizole is a potent inhibitor of alcohol dehydrogenase and is the preferred antidote to prevent the formation of these toxic metabolites. While sodium bicarbonate may be used to correct acidosis, it is not the primary antidote. Naloxone is for opioid overdose, and acetylcysteine is for acetaminophen toxicity.

Question 77: Which oncogene is characteristically amplified in neuroblastoma and correlates with poor prognosis?

RET
BCR-ABL
HER2/NEU
N-MYC (Correct answer)

Correct answer: N-MYC

N-MYC (MYCN) amplification in neuroblastoma is associated with rapid tumor progression and poor prognosis.

Question 78: Which mechanism allows Staphylococcus aureus to resist beta-lactam antibiotics such as methicillin (MRSA) in veterinary patients?

Acquisition of mecA gene encoding a modified penicillin-binding protein (PBP2a) with low antibiotic affinity (Correct answer)
Production of extended-spectrum beta-lactamase (ESBL) that hydrolyzes the beta-lactam ring
Efflux pumps that expel beta-lactam antibiotics from the bacterial cell
Reduced outer membrane permeability preventing antibiotic entry

Correct answer: Acquisition of mecA gene encoding a modified penicillin-binding protein (PBP2a) with low antibiotic affinity

The mecA gene encodes PBP2a, an altered penicillin-binding protein with very low affinity for all beta-lactam antibiotics, conferring broad resistance in MRSA strains.

Question 79: A dog presents with acute, painful unilateral blindness, a mid-dilated unresponsive pupil, corneal edema, and intraocular pressure of 58 mmHg. The most likely diagnosis is:

Acute primary glaucoma (Correct answer)
Anterior uveitis
Retinal detachment
Corneal ulcer with descemetocele

Correct answer: Acute primary glaucoma

Acute primary glaucoma (most commonly closed-angle in dogs) presents with markedly elevated IOP (>30 mmHg, often 40–70 mmHg), corneal edema from endothelial damage, fixed mid-dilated pupil, and rapid onset of blindness. It is an ocular emergency requiring immediate IOP reduction. Uveitis typically causes miosis and low-to-normal IOP. Retinal detachment causes blindness without pain or elevated IOP. Corneal ulcers cause pain and discharge but not elevated IOP.

Question 80: A 4-year-old intact male cat presents with urethral obstruction. After relief and stabilization, bloodwork reveals severe hyperkalemia causing bradycardia. Physiologically, which mechanism best explains why hyperkalemia depresses cardiac automaticity and slows conduction in feline myocardium?

Elevated extracellular K⁺ reduces the resting membrane potential (makes it less negative) by decreasing the K⁺ equilibrium potential, which inactivates voltage-gated fast Na⁺ channels and reduces phase 0 upstroke velocity (Correct answer)
Elevated extracellular K⁺ activates the Na⁺/K⁺-ATPase pump maximally, causing excessive Na⁺ extrusion that hyperpolarizes nodal pacemaker cells and suppresses spontaneous depolarization
Elevated extracellular K⁺ hyperpolarizes the resting membrane potential of nodal cells by increasing the electrochemical gradient for K⁺ efflux, making it harder to reach threshold
Elevated extracellular K⁺ prolongs phase 2 of the action potential by competitively blocking L-type Ca²⁺ channels, slowing repolarization and extending the refractory period

Correct answer: Elevated extracellular K⁺ reduces the resting membrane potential (makes it less negative) by decreasing the K⁺ equilibrium potential, which inactivates voltage-gated fast Na⁺ channels and reduces phase 0 upstroke velocity

Extracellular potassium concentration directly determines the K⁺ equilibrium potential (Ek) via the Nernst equation. As extracellular K⁺ rises, Ek becomes less negative, which depolarizes the resting membrane potential (RMP) of all cardiac cells. While this initial, modest depolarization might paradoxically seem excitatory, the sustained partial depolarization causes voltage-gated fast Na⁺ channels (responsible for phase 0 in working myocytes and ventricular conduction) to enter an inactivated (non-conducting) state — they cannot open again without full repolarization. The result is reduced phase 0 upstroke velocity (dV/dt), slower conduction velocity, widened QRS, and bradycardia. Option A is incorrect because hyperkalemia depolarizes, not hyperpolarizes, the RMP. Options C and D describe mechanisms not primarily responsible for hyperkalemia's cardiac effects.

Question 81: Which nutrient deficiency causes 'white muscle disease' (nutritional myodegeneration) in calves and lambs?

Vitamin A deficiency
Copper deficiency
Selenium and/or vitamin E deficiency (Correct answer)
Calcium deficiency

Correct answer: Selenium and/or vitamin E deficiency

White muscle disease results from inadequate selenium and/or vitamin E, antioxidants that protect muscle membranes from oxidative damage.

Question 82: A zoo is housing a solitary-in-the-wild felid species in an exhibit that provides hiding spaces, elevated platforms, and multiple olfactory enrichment stations. Staff report the animal exhibits pacing stereotypies for >3 hours/day. Which welfare assessment framework would MOST accurately identify whether this stereotypy represents a current versus historical welfare deficit?

Applying the Five Freedoms framework to audit all five domains and score each as met or unmet
Measuring behavioral flexibility: if the stereotypy is still interruptible by novel enrichment stimuli, it likely reflects current welfare deficiency rather than an established fixed action pattern (Correct answer)
Calculating the percentage of time budget deviation from published wild conspecific behavioral profiles
Assessing glucocorticoid metabolite concentrations in fecal samples collected over 14 days

Correct answer: Measuring behavioral flexibility: if the stereotypy is still interruptible by novel enrichment stimuli, it likely reflects current welfare deficiency rather than an established fixed action pattern

Stereotypies can arise under poor welfare conditions ('current deficit') but may also persist as behavioral scars even after welfare improves ('historical deficit'). The critical discriminator is behavioral flexibility: if the stereotypy can be interrupted by appropriate novel stimuli — meaning the animal redirects attention and suspends the behavior — this suggests ongoing motivational frustration. A 'crystallized' or fixed stereotypy that has become emancipated from its original motivational state is less responsive to interruption. The Five Freedoms framework is an audit tool but does not temporally distinguish current from historical origin. Fecal glucocorticoids reflect current stress axis activation but cannot discriminate stereotypy origin. Wild time-budget comparisons indicate deviation but not the cause.

Question 83: Which of the following is a TRUE statement about the use of drains in surgical wounds?

Drains should routinely exit through the primary incision
Active closed-suction drains (e.g., Jackson-Pratt) are preferred over passive drains for most wounds (Correct answer)
Drains should be left in place for a minimum of 14 days regardless of output
Passive drains prevent all surgical site infections

Correct answer: Active closed-suction drains (e.g., Jackson-Pratt) are preferred over passive drains for most wounds

Active closed-suction drains provide controlled negative pressure, reduce fluid accumulation more effectively, and lower infection risk compared to passive open drains.

Question 84: A meta-analysis of 15 randomized trials examining beta-blocker use post-MI produces a funnel plot that is markedly asymmetric, with small studies clustered on one side showing larger effect sizes. The Egger's test is statistically significant (p = 0.03). Which of the following represents the MOST methodologically rigorous next step to address this finding?

Accept the pooled result as valid because 15 trials provide sufficient statistical power to overcome publication bias
Apply the trim-and-fill method to impute missing studies and recalculate the pooled effect size, then assess whether the adjusted estimate remains clinically significant (Correct answer)
Exclude all small studies (n < 100) from the meta-analysis to eliminate the source of asymmetry
Conduct a subgroup analysis stratified by study quality score to determine whether heterogeneity explains the asymmetry

Correct answer: Apply the trim-and-fill method to impute missing studies and recalculate the pooled effect size, then assess whether the adjusted estimate remains clinically significant

Funnel plot asymmetry with a significant Egger's test strongly suggests publication bias (though heterogeneity and true small-study effects are also possible causes). The trim-and-fill method is the standard next step: it imputes the theoretically missing studies on the opposite side of the funnel and recalculates the pooled estimate. If the adjusted estimate remains clinically meaningful, the conclusion is more robust. Simply excluding small studies introduces selection bias; accepting the result ignores potential overestimation; subgroup analysis by quality addresses heterogeneity but not publication bias directly.

Question 85: The greater omentum in dogs is a peritoneal fold that primarily originates from which organ?

Descending duodenum
Spleen
Liver
Greater curvature of the stomach (Correct answer)

Correct answer: Greater curvature of the stomach

The greater omentum arises from the greater curvature of the stomach and drapes over the intestines, playing roles in fat storage and immune defense.

Question 86: A researcher conducts a prospective cohort study and calculates an attributable risk percent (AR%) of 60% for smoking and lung cancer. A policy maker asks what this statistic means for public health planning. Which interpretation is most accurate?

60% of all lung cancer in the general population is due to smoking
Eliminating smoking would reduce overall population lung cancer incidence by 60%
60% of lung cancer cases in smokers are attributable to smoking itself (Correct answer)
Smokers have a 60% absolute risk of developing lung cancer

Correct answer: 60% of lung cancer cases in smokers are attributable to smoking itself

Attributable risk percent (AR%) — also called etiologic fraction among the exposed — represents the proportion of disease in the exposed group that is attributable to the exposure. It equals (RR−1)/RR × 100. An AR% of 60% means that 60% of lung cancer cases occurring among smokers would be prevented if smoking were eliminated. Reducing population-level incidence by 60% would require the population attributable risk percent (PAR%), which also accounts for prevalence of exposure in the population.

Question 87: During prolonged starvation (>5 days), the brain reduces its glucose dependency by utilizing ketone bodies. Which enzymatic step is rate-limiting for ketone body UTILIZATION in neurons, and why cannot the liver use this same pathway?

Acetyl-CoA acetyltransferase (thiolase), which is inhibited by high hepatic NADH
Succinyl-CoA:3-ketoacid CoA transferase (SCOT), which is absent in hepatocytes (Correct answer)
β-hydroxybutyrate dehydrogenase, which is downregulated in fasting liver
HMG-CoA lyase, which is exclusively expressed in mitochondria of extrahepatic tissues

Correct answer: Succinyl-CoA:3-ketoacid CoA transferase (SCOT), which is absent in hepatocytes

Ketone body utilization requires succinyl-CoA:3-ketoacid CoA transferase (SCOT, also called 3-oxoacid CoA-transferase) to transfer CoA from succinyl-CoA to acetoacetate, forming acetoacetyl-CoA for further oxidation. Hepatocytes constitutively lack SCOT expression — this is not a regulatory downregulation but a permanent absence — which prevents the liver from oxidizing the ketone bodies it produces. This tissue-specific enzyme absence ensures hepatically-synthesized ketones are obligately exported as fuel for extrahepatic organs including the brain.

Question 88: A horse presents with symmetric ataxia and weakness in all four limbs, with hindlimbs more severely affected. Necropsy reveals demyelination and axonal degeneration most concentrated at the cervical intumescence. Which region of the spinal cord contains the neuronal cell bodies whose axons project to the forelimb musculature and would be most directly damaged in this region?

Clarke's nucleus (nucleus thoracicus) of C8–L3
Dorsal horn laminae I–IV of C1–C5
Ventral horn of C6–T2 (Correct answer)
Intermediolateral cell column of T1–T3

Correct answer: Ventral horn of C6–T2

The cervical intumescence (C6–T2 in horses) contains the lower motor neuron cell bodies in the ventral horn whose axons form the brachial plexus and innervate forelimb musculature. Damage here produces LMN signs in the forelimbs. Clarke's nucleus relays proprioception. The intermediolateral column provides preganglionic sympathetic innervation. The dorsal horn processes sensory input.

Question 89: Which vaccine-preventable disease has a global eradication goal as of current WHO targets?

Diphtheria
Measles
Poliomyelitis (Correct answer)
Tetanus

Correct answer: Poliomyelitis

The Global Polio Eradication Initiative aims to eradicate all wild poliovirus strains, following smallpox as the second human disease to be eradicated.

Question 90: Which enzyme deficiency leads to phenylketonuria (PKU), resulting in accumulation of phenylalanine?

Phenylalanine hydroxylase (Correct answer)
Fumarylacetoacetase
Tyrosine hydroxylase
Homogentisate oxidase

Correct answer: Phenylalanine hydroxylase

PKU results from deficiency of phenylalanine hydroxylase, the enzyme that converts phenylalanine to tyrosine in the liver.

Question 91: Which of the following electrolyte abnormalities is most commonly associated with grain overload (carbohydrate engorgement) in cattle?

Hypocalcemia
Hyperkalemia
Metabolic acidosis with D-lactatemia (Correct answer)
Hypernatremia

Correct answer: Metabolic acidosis with D-lactatemia

Grain overload causes rapid fermentation producing D-lactic acid, leading to metabolic acidosis and D-lactatemia, which can be severe and life-threatening.

Question 92: A ferret presents for adrenalectomy. Which vessel must be carefully preserved or managed to avoid serious intraoperative hemorrhage, particularly during right adrenalectomy?

Hepatic artery
Mesenteric artery
Portal vein
Caudal vena cava (Correct answer)

Correct answer: Caudal vena cava

The right adrenal gland is intimately associated with the caudal vena cava, and inadvertent laceration during right adrenalectomy can cause life-threatening hemorrhage.

Question 93: Which of the following best describes the rationale for administering prophylactic antibiotics in veterinary surgery?

They are given to achieve bactericidal tissue concentrations at the time of incision to reduce surgical site infection risk (Correct answer)
They are indicated for all surgeries regardless of wound classification
They eliminate the need for sterile technique
They should be continued for at least 14 days postoperatively to ensure efficacy

Correct answer: They are given to achieve bactericidal tissue concentrations at the time of incision to reduce surgical site infection risk

Prophylactic antibiotics must be present in tissues at the time of incision; they reduce bacterial contamination during surgery but do not replace sterile technique or extend the postoperative course unnecessarily.

Question 94: During an intestinal resection and anastomosis, a surgeon needs to temporarily occlude the bowel lumen proximal and distal to the surgical site to prevent leakage of contents. Which of the following instruments is designed for this purpose, causing minimal trauma to the intestinal wall?

Carmalt forceps
Babcock forceps
Doyen intestinal forceps (Correct answer)
Allis tissue forceps

Correct answer: Doyen intestinal forceps

Doyen intestinal forceps are specifically designed to be atraumatic. They have longitudinal serrations and flexible, bowed jaws that allow for temporary occlusion of the bowel lumen without crushing the tissue or compromising its blood supply. Carmalt forceps are crushing hemostats used on vessels or pedicles. Allis tissue forceps are traumatic and used for grasping tissue that will be removed. Babcock forceps are less traumatic than Allis but are for grasping and retracting, not occluding a lumen.

Question 95: Sarcocystis neurona is the primary causative agent of equine protozoal myeloencephalitis (EPM). What is the definitive host of this organism?

Raccoon
White-tailed deer
Armadillo
Opossum (Didelphis virginiana) (Correct answer)

Correct answer: Opossum (Didelphis virginiana)

The Virginia opossum (Didelphis virginiana) is the definitive host of Sarcocystis neurona, shedding sporocysts in its feces that contaminate horse feed and water.

Question 96: On a plain radiograph, which feature best distinguishes a pathologic fracture from a stress fracture?

Bilateral symmetric involvement
Location at the femoral neck
An underlying lytic or blastic lesion at the fracture site (Correct answer)
Periosteal reaction along the fracture line

Correct answer: An underlying lytic or blastic lesion at the fracture site

A pathologic fracture occurs through pre-existing bone disease, so identifying an underlying lesion at the fracture site is the key distinguishing feature.

Question 97: When assessing pain in a domestic rabbit using validated scoring tools, which behavioral indicator is MOST specific to acute pain rather than fear or general stress?

Freezing behavior and reduced exploratory activity
Increased respiratory rate and piloerection
Thumping hindlimbs and flattened ear posture
Orbital tightening and whisker position change scored by the Rabbit Grimace Scale (Correct answer)

Correct answer: Orbital tightening and whisker position change scored by the Rabbit Grimace Scale

The Rabbit Grimace Scale (RbtGS) is a validated, species-specific facial action coding tool that scores orbital tightening, cheek flattening, nose shape changes, whisker position, and ear position to quantify acute pain. Critically, facial grimace scales are more specific for pain than behavioral changes like freezing, thumping, or piloerection, which can be elicited by fear or general arousal. Orbital tightening and altered whisker position are the most reliably pain-specific components.

Question 98: A veterinarian performs a celiotomy on a horse and identifies the cecum. Which anatomical landmark most reliably distinguishes the right dorsal colon from the cecum when both are distended and visible simultaneously?

The right dorsal colon has a smooth serosal surface with no taeniae in its proximal third
The cecum has four longitudinal taeniae and four rows of sacculations (haustra), whereas the right dorsal colon has only three taeniae (Correct answer)
The cecocolic orifice is located on the medial band of the cecum's apex, distinguishing it from any colonic segment
The cecum is positioned entirely on the left side of the abdomen in the standing horse

Correct answer: The cecum has four longitudinal taeniae and four rows of sacculations (haustra), whereas the right dorsal colon has only three taeniae

The equine cecum bears four taeniae (bands) and four rows of sacculations. The right ventral colon has four taeniae, but the right dorsal colon transitions to having only three taeniae as it courses toward the transverse colon. Intraoperatively, counting taeniae on a distended viscus is a reliable quick differentiator. The cecum is located on the right side of the abdomen (not left), and the cecocolic orifice is on the medial surface of the body — near the base, not the apex.

Question 99: A patient taking isoniazid for tuberculosis develops peripheral neuropathy. What is the mechanism of this adverse effect?

Isoniazid chelates magnesium required for axonal conduction
Isoniazid induces CYP2E1 producing hepatotoxic metabolites that damage peripheral nerves
Isoniazid competes with pyridoxine (vitamin B6) for binding to apoenymes (Correct answer)
Isoniazid directly inhibits myelin basic protein synthesis in Schwann cells

Correct answer: Isoniazid competes with pyridoxine (vitamin B6) for binding to apoenymes

Isoniazid forms hydrazones with pyridoxal phosphate (active B6), depleting the coenzyme needed for GABA synthesis and amino acid metabolism in peripheral neurons, causing neuropathy preventable with B6 supplementation.

Question 100: Which endocrine gland is located near the thyroid in dogs and produces parathyroid hormone (PTH) to regulate calcium homeostasis?

Pineal gland
Parathyroid gland (Correct answer)
Thymus
Adrenal medulla

Correct answer: Parathyroid gland

The parathyroid glands, typically four small glands associated with the thyroid, secrete PTH which raises blood calcium by stimulating bone resorption and renal calcium retention.

Question 101: On CT of the chest, which finding is most suggestive of a malignant solitary pulmonary nodule rather than a benign granuloma?

Laminated calcification throughout the nodule
Smooth margins with a small diameter <6 mm
Spiculated margins with a diameter >8 mm and no central calcification (Correct answer)
Dense central or 'popcorn' calcification

Correct answer: Spiculated margins with a diameter >8 mm and no central calcification

Spiculated margins, size >8 mm, and absence of benign calcification patterns are the highest-risk CT features for malignancy in a pulmonary nodule.

Question 102: A 3-year-old llama presents with progressive weight loss, bottle jaw, pale mucous membranes, and a fecal egg count of 8,500 Haemonchus contortus eggs per gram. The owner has been rotating between ivermectin and benzimidazoles every 60 days. Fecal egg count reduction tests show <70% reduction with both drug classes. Which anthelmintic regimen is NOW considered the most appropriate next step?

Triple combination therapy: ivermectin + levamisole + oxfendazole at standard doses (Correct answer)
Monepantel administered at the label dose for small ruminants
Closantel given orally, leveraging its adulticidal activity against blood-feeding nematodes
Moxidectin at 5× the standard dose to overcome macrocyclic lactone resistance

Correct answer: Triple combination therapy: ivermectin + levamisole + oxfendazole at standard doses

Multi-drug resistance to both macrocyclic lactones and benzimidazoles is confirmed by the FECRT results. Current evidence-based guidelines for anthelmintic-resistant Haemonchus in camelids and small ruminants recommend triple combination therapy using one drug from each major class (ML + levamisole + benzimidazole) simultaneously, as resistant alleles to all three classes simultaneously are rare. This approach is supported by FAMACHA-guided targeted selective treatment. Monepantel (amino-acetonitrile derivative) is registered in some countries but not currently approved in the US for camelids and efficacy data are limited. High-dose moxidectin does not reliably overcome confirmed resistance and increases toxicity risk. Closantel is not approved in North America and resistance develops rapidly.

Question 103: Which enzyme is primarily responsible for metabolizing warfarin in the liver?

CYP2D6
CYP2C9 (Correct answer)
CYP3A4
CYP1A2

Correct answer: CYP2C9

CYP2C9 is the primary hepatic enzyme responsible for the metabolism of the S-enantiomer of warfarin, which accounts for most of its anticoagulant activity.

Question 104: During frozen section analysis of a sentinel lymph node from a breast cancer patient, you observe a 0.6 mm cluster of cytokeratin-positive epithelial cells within the subcapsular sinus. No other nodes are submitted. According to the AJCC 8th Edition, how should this finding be classified and what is the resulting nodal stage?

Cannot be classified on frozen section; defer to permanent sections only
Isolated tumor cells (ITC); pN0(i+)
Micrometastasis; pN1mi (Correct answer)
Macrometastasis; pN1a

Correct answer: Micrometastasis; pN1mi

Per AJCC 8th Edition, micrometastases are defined as tumor deposits > 0.2 mm but ≤ 2.0 mm, staged as pN1mi. At 0.6 mm, this deposit exceeds the 0.2 mm threshold for isolated tumor cells (ITC, classified pN0(i+) when ≤ 0.2 mm or ≤ 200 cells) but is well below the 2.0 mm threshold for macrometastasis (pN1a). ITCs are specifically ≤ 0.2 mm clusters or single cells, so 0.6 mm qualifies as a micrometastasis regardless of method of detection.

Question 105: Which of the following sterilization methods is most appropriate for a heat-sensitive, moisture-sensitive flexible endoscope?

Dry heat oven
Ethylene oxide gas (Correct answer)
Steam autoclave
Boiling water immersion

Correct answer: Ethylene oxide gas

Ethylene oxide (EtO) gas sterilization is a low-temperature process effective for items that cannot withstand the high temperatures and moisture of steam autoclaving, such as flexible endoscopes and certain plastics. Steam, dry heat, and boiling would damage the delicate components of the endoscope.

Question 106: Beta-blockers are contraindicated in patients with reactive airway disease primarily because they:

Reduce mucociliary clearance by inhibiting beta-2-mediated secretion
Decrease hypoxic pulmonary vasoconstriction by vasodilating pulmonary vessels
Inhibit beta-1 receptors in sinoatrial node, worsening hypoxia-induced tachycardia
Block beta-2 receptors in bronchial smooth muscle, causing bronchoconstriction (Correct answer)

Correct answer: Block beta-2 receptors in bronchial smooth muscle, causing bronchoconstriction

Non-selective beta-blockers block beta-2 adrenergic receptors in bronchial smooth muscle, preventing epinephrine-mediated bronchodilation and triggering potentially life-threatening bronchoconstriction in asthmatic patients.

Question 107: A high-producing dairy cow that calved 24 hours ago is found in sternal recumbency with an S-shaped curve to her neck. She is afebrile and unable to rise. This presentation is most consistent with parturient paresis. What is the primary metabolic disturbance responsible for this condition?

Hyperkalemia
Hypoglycemia
Hypocalcemia (Correct answer)
Hypomagnesemia

Correct answer: Hypocalcemia

Parturient paresis, or milk fever, is caused by an acute drop in blood calcium levels (hypocalcemia). This occurs at the onset of lactation when the demand for calcium for colostrum and milk production suddenly and massively exceeds the body's ability to mobilize calcium from the diet and bone stores. The clinical signs of muscle weakness, recumbency, and flaccid paralysis are direct consequences of low extracellular calcium.

Question 108: A 9-year-old cat presents with progressive weight loss, polyphagia, and a palpable ventral neck mass. T4 is markedly elevated. After confirming hyperthyroidism, which treatment option provides the best chance of permanent cure?

Radioactive iodine (I-131) therapy (Correct answer)
Bilateral thyroidectomy
Dietary iodine restriction alone
Oral methimazole for life

Correct answer: Radioactive iodine (I-131) therapy

Radioactive iodine (I-131) is considered the gold standard curative treatment for feline hyperthyroidism with >95% cure rate and minimal complications.

Question 109: A 4-year-old child ingests an unknown quantity of a grandparent's iron supplement tablets. In the emergency department, the child develops metabolic acidosis, coagulopathy, and elevated serum ferritin. Which mechanism accounts for the metabolic acidosis seen in acute iron toxicity?

Iron inhibits carbonic anhydrase in red blood cells, impairing CO2 transport
Iron chelates bicarbonate in the bloodstream, directly consuming buffer
Free ferric iron catalyzes the Fenton reaction generating hydroxyl radicals that disrupt mitochondrial oxidative phosphorylation, causing lactic acidosis (Correct answer)
Iron-induced emesis causes chloride loss, generating a hypochloremic alkalosis that is masked by concurrent lactic acidosis

Correct answer: Free ferric iron catalyzes the Fenton reaction generating hydroxyl radicals that disrupt mitochondrial oxidative phosphorylation, causing lactic acidosis

In acute iron toxicity, excess free iron (Fe²⁺/Fe³⁺) catalyzes the Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + ·OH), generating highly reactive hydroxyl radicals. These radicals cause lipid peroxidation of mitochondrial membranes, uncoupling oxidative phosphorylation and shifting cellular metabolism to anaerobic glycolysis. The resultant lactate accumulation produces an elevated anion gap metabolic acidosis. This is compounded by direct cellular toxicity to hepatocytes and GI epithelium.

Question 110: A 4-year-old Standardbred presents with intermittent hindlimb ataxia that worsens with the head elevated. Cervical radiographs show vertebral canal stenosis at C3-C4. What is the most likely diagnosis?

Equine herpesvirus-1 myeloencephalopathy
Equine protozoal myeloencephalitis (EPM)
Equine degenerative myeloencephalopathy (EDM)
Cervical vertebral stenotic myelopathy (Wobbler syndrome) (Correct answer)

Correct answer: Cervical vertebral stenotic myelopathy (Wobbler syndrome)

Wobbler syndrome causes proprioceptive ataxia that worsens with neck extension/elevation due to dynamic or static spinal cord compression at cervical vertebral articulations.

Question 111: In performing a diaphragmatic herniorrhaphy in a cat with a chronic (>2 week) traumatic diaphragmatic hernia, which of the following physiological phenomena presents the greatest anesthetic risk specific to the re-expansion phase of the repair?

Acute hyperkalemia from reperfusion of ischemic bowel segments repositioned into the abdomen
Re-expansion pulmonary edema due to rapid inflation of chronically atelectatic lung lobes (Correct answer)
Tension pneumothorax from residual pleural air unable to be evacuated before closure
Paradoxical acidosis from sudden shift of abdominal viscera back into the peritoneal cavity

Correct answer: Re-expansion pulmonary edema due to rapid inflation of chronically atelectatic lung lobes

Re-expansion pulmonary edema (RPE) is a well-documented complication when chronically atelectatic lung lobes are rapidly re-expanded. In chronic diaphragmatic hernias, the displaced lung has been collapsed for weeks; sudden re-expansion causes increased vascular permeability from mechanical stress and reperfusion injury to the alveolar-capillary membrane, leading to non-cardiogenic pulmonary edema. This is the anesthetic/surgical risk most specific to the re-expansion phase. Tension pneumothorax is managed by routine thoracic drainage. Hyperkalemia from bowel reperfusion is possible but not as specifically tied to the re-expansion phase itself.

Question 112: In ruminants, the reticulo-omasal orifice (ROO) plays a critical gating role in digesta flow. Which neurological mechanism is PRIMARILY responsible for the reflex relaxation of the ROO that allows passage of liquid digesta from the reticulum to the omasum?

Vagal efferent (parasympathetic) non-adrenergic, non-cholinergic (NANC) inhibitory neurons releasing VIP (Correct answer)
Intrinsic myenteric plexus neurons triggered by luminal distension of the omasal canal
Sympathetic stimulation via splanchnic nerves causing smooth muscle relaxation through β2-adrenergic receptors
Hormonal relaxation mediated by motilin released from Mo cells in the reticulum

Correct answer: Vagal efferent (parasympathetic) non-adrenergic, non-cholinergic (NANC) inhibitory neurons releasing VIP

Relaxation of the reticulo-omasal orifice is mediated by vagal efferent non-adrenergic, non-cholinergic (NANC) inhibitory neurons whose primary neurotransmitter is vasoactive intestinal peptide (VIP), along with nitric oxide. This vagal NANC pathway is coordinated with the biphasic reticulo-ruminal contraction cycle — the ROO relaxes during the second phase of the reticulo-ruminal contraction, allowing fluid digesta to pass. The sympathetic system generally inhibits GI motility but is not the primary gating reflex here; motilin is more relevant to the migrating myoelectric complex in monogastrics.

Question 113: A young German Shepherd is presented with a history of chronic diarrhea and significant weight loss despite a ravenous appetite. Which of the following clinical signs is most characteristic of exocrine pancreatic insufficiency (EPI)?

Melena and intermittent vomiting
Polyuria and polydipsia
Steatorrhea and polyphagia (Correct answer)
Jaundice and ascites

Correct answer: Steatorrhea and polyphagia

Exocrine pancreatic insufficiency (EPI) is a condition of maldigestion caused by insufficient production of digestive enzymes by the pancreas. The classic clinical signs include polyphagia (ravenous appetite), significant weight loss, and steatorrhea (large volumes of pale, fatty, malodorous feces) due to the inability to digest fats.

Question 114: On a nuclear medicine bone scan, which pattern is most characteristic of metastatic prostate cancer?

Multiple asymmetric areas of increased uptake (hot spots) in the axial skeleton (Correct answer)
Increased uptake symmetrically at all joint spaces
A single hot spot in the long bone diaphysis
Diffusely decreased uptake throughout the skeleton

Correct answer: Multiple asymmetric areas of increased uptake (hot spots) in the axial skeleton

Prostate cancer metastases are typically osteoblastic, producing multiple asymmetric hot spots predominantly in the axial skeleton on bone scintigraphy.

Question 115: Which measure of central tendency is least affected by extreme outliers?

Mode
Weighted average
Mean
Median (Correct answer)

Correct answer: Median

The median is the middle value of a distribution and is resistant to the influence of extreme values (outliers) unlike the mean.

Question 116: A cat presents with a wound that is 72 hours old and moderately contaminated. What is the most appropriate wound management strategy?

Delayed primary closure after wound preparation (Correct answer)
Second-intention healing without debridement
Immediate skin grafting
Primary closure immediately

Correct answer: Delayed primary closure after wound preparation

Wounds older than 6–8 hours that are contaminated are best managed with debridement and delayed primary closure once infection risk is reduced.

Question 117: In the bitch, serum progesterone concentrations above 5 ng/mL typically indicate which reproductive event?

Ovulation has occurred (Correct answer)
Anestrus
Proestrus onset
LH surge

Correct answer: Ovulation has occurred

Progesterone rises above 5 ng/mL after ovulation in the bitch, confirming that ovulation has already taken place.

Question 118: A country implements a mandatory fortification program adding folic acid to all flour products. Five years later, epidemiologists observe a paradoxical increase in the reported incidence of neural tube defects (NTDs). Which of the following is the MOST likely explanation for this finding?

Competitive inhibition of folate metabolism by unmetabolized folic acid at high doses
Depletion of maternal folate stores during the fortification transition period
Teratogenic effect of synthetic folic acid differing from naturally occurring folate
Improved case ascertainment and surveillance infrastructure capturing previously missed diagnoses (Correct answer)

Correct answer: Improved case ascertainment and surveillance infrastructure capturing previously missed diagnoses

Paradoxical increases in disease incidence following public health interventions are classically explained by Will Rogers phenomenon or, more commonly here, improved case ascertainment. When a program is implemented, it often comes with enhanced surveillance, better diagnostic criteria, and improved reporting systems. Previously missed NTD cases (stillbirths, early fetal losses, or unreported live births) begin to be captured. This surveillance artifact must be ruled out before concluding that an intervention is ineffective or harmful.

Question 119: A critically ill patient on prolonged parenteral nutrition develops hypophosphatemia, hemolytic anemia, and reduced diaphragmatic contractility. Which metabolic mechanism best explains these findings collectively?

Zinc deficiency impairing carbonic anhydrase activity in erythrocytes
Excess glucose infusion suppressing fatty acid oxidation and causing mitochondrial uncoupling
ATP depletion secondary to intracellular phosphate deficiency disrupting energy-dependent cell functions (Correct answer)
Depletion of 2,3-diphosphoglycerate impairing oxygen delivery to tissues

Correct answer: ATP depletion secondary to intracellular phosphate deficiency disrupting energy-dependent cell functions

Refeeding syndrome causes profound hypophosphatemia as glucose infusion drives phosphate intracellularly for ATP synthesis. The resulting intracellular phosphate depletion reduces ATP availability in erythrocytes (causing hemolytic anemia from membrane pump failure) and respiratory muscles (reducing diaphragmatic contractility). While 2,3-DPG depletion also occurs and shifts the oxygen-dissociation curve, the unifying mechanism across all three findings is generalized ATP depletion from phosphate deficiency.

Question 120: In the context of infectious disease control, 'quarantine' differs from 'isolation' in that quarantine applies to:

Healthcare workers after needlestick injuries
Confirmed infectious cases only
Exposed individuals who may or may not be infected (Correct answer)
Deceased persons with infectious diseases

Correct answer: Exposed individuals who may or may not be infected

Quarantine restricts movement of exposed but potentially uninfected individuals, while isolation separates confirmed or suspected cases from others.

Question 121: Which pharmacokinetic model best describes the distribution of intravenous anesthetics after a bolus dose?

One-compartment model
Three-compartment model (Correct answer)
Michaelis-Menten kinetics
Zero-order kinetics

Correct answer: Three-compartment model

IV anesthetics are best described by a three-compartment model: central (plasma), rapidly equilibrating peripheral (vessel-rich tissues), and slowly equilibrating peripheral (muscle, fat).

Question 122: A 28-year-old patient with a known history of malignant hyperthermia (MH) susceptibility requires general anesthesia for an appendectomy. The anesthesiologist plans a TIVA technique. Which of the following is also mandatory before starting the case?

Flushing the anesthesia machine with 100% oxygen at ≥10 L/min for at least 20 minutes and replacing circuit components to remove residual volatile agent (Correct answer)
Avoiding succinylcholine but proceeding normally with the standard anesthesia machine
Pre-treatment with dantrolene 2.5 mg/kg IV to prevent MH
Canceling the case and performing it under epidural anesthesia only

Correct answer: Flushing the anesthesia machine with 100% oxygen at ≥10 L/min for at least 20 minutes and replacing circuit components to remove residual volatile agent

For MH-susceptible patients receiving TIVA, prophylactic dantrolene is NOT routinely recommended — it is reserved for active MH crises (or occasionally high-risk cases per institutional protocol). However, the anesthesia machine MUST be prepared by flushing with high-flow O2 (≥10 L/min) for at least 20 minutes and removing vaporizers (or using charcoal filters per manufacturer guidance) to eliminate residual volatile anesthetic from circuits and rubber components, which can trigger MH. Simply avoiding succinylcholine while using the contaminated machine is insufficient. The case need not be cancelled if TIVA with a prepared machine is used.

Question 123: Which antifungal mechanism of action does amphotericin B use to kill fungal cells?

Binds ergosterol, forming pores that disrupt membrane integrity (Correct answer)
Inhibits beta-glucan synthase in the cell wall
Inhibits lanosterol 14-alpha-demethylase
Blocks fungal DNA gyrase

Correct answer: Binds ergosterol, forming pores that disrupt membrane integrity

Amphotericin B binds ergosterol in the fungal cell membrane and creates transmembrane pores, causing lethal leakage of intracellular ions.

Question 124: Which mechanism explains the development of tolerance to opioids with chronic use?

Increased hepatic first-pass metabolism
Competitive antagonism at mu receptors
Upregulation of adenylyl cyclase activity
Receptor desensitization and downregulation (Correct answer)

Correct answer: Receptor desensitization and downregulation

Chronic opioid exposure leads to desensitization and downregulation of mu-opioid receptors, requiring higher doses to achieve the same analgesic effect.

Question 125: A 5-year-old warmblood mare presents with a 2-week history of ventral edema, weight loss, protein-losing enteropathy confirmed by elevated fecal alpha-1-protease inhibitor, hypoalbuminemia (1.4 g/dL), and panhypoproteinemia. Rectal mucosal biopsy shows villous atrophy and granulomatous inflammation. Peritoneal fluid analysis reveals a clear transudate. Which diagnosis is MOST consistent with this constellation of findings in the adult horse?

Granulomatous enteritis (idiopathic multisystemic eosinophilic epitheliotropic disease) (Correct answer)
Equine proliferative enteropathy (Lawsonia intracellularis)
Cyathostominosis with larval cyathostome emergence
Right dorsal colitis secondary to NSAID toxicosis

Correct answer: Granulomatous enteritis (idiopathic multisystemic eosinophilic epitheliotropic disease)

Granulomatous enteritis / multisystemic eosinophilic epitheliotropic disease (MEED) in adult horses presents with chronic protein-losing enteropathy, panhypoproteinemia, weight loss, and villous atrophy with granulomatous inflammation on biopsy. The peritoneal transudate reflects oncotic pressure loss, not inflammation. Equine proliferative enteropathy (EPE) from Lawsonia intracellularis predominantly affects weanlings and yearlings (3–6 months), not 5-year-old adults, and produces intracellular curved rods on silver stain. Cyathostominosis causes diarrhea, edema, and larval emergence typhlocolitis but biopsy shows larval stages, not granulomatous inflammation. Right dorsal colitis causes focal thickening of the right dorsal colon on ultrasound with a history of NSAID use, and does not cause villous atrophy.

Question 126: A 58-year-old patient presents with a solitary pulmonary nodule on CT. The nodule measures 12 mm, has a spiculated margin, and demonstrates a CT attenuation value of -40 HU. Which characteristic is MOST consistent with a benign hamartoma rather than malignancy?

Fat attenuation (-40 HU) within the lesion (Correct answer)
Size greater than 10 mm
Spiculated margin
Absence of calcification

Correct answer: Fat attenuation (-40 HU) within the lesion

Fat attenuation (negative HU values, typically between -40 and -120 HU) within a pulmonary nodule is a hallmark feature of pulmonary hamartoma, a benign lesion. Hamartomas are composed of cartilage, fat, connective tissue, and epithelium. Spiculated margins and size >10 mm are features more suggestive of malignancy, while absence of calcification is non-specific.

Question 127: A 65-year-old male has a renal mass removed surgically. Histology shows clear cells arranged in nests with a rich vascular network. Immunohistochemistry shows positivity for CD10 and PAX8 and negativity for CK7. What is the diagnosis?

Chromophobe renal cell carcinoma
Oncocytoma
Papillary renal cell carcinoma
Clear cell renal cell carcinoma (Correct answer)

Correct answer: Clear cell renal cell carcinoma

Clear cell RCC shows clear cytoplasm due to glycogen and lipid accumulation, is CD10+ and PAX8+, and typically CK7-negative, distinguishing it from papillary and chromophobe RCC.

Question 128: A horse with confirmed equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona is started on treatment. Which drug combination is FDA-approved specifically for EPM treatment in horses?

Pyrimethamine and sulfadiazine
Ponazuril or diclazuril monotherapy
Both B and C are approved options (Correct answer)
Metronidazole and rifampin

Correct answer: Both B and C are approved options

Ponazuril (Marquis), diclazuril (Protazil), and the combination of pyrimethamine/sulfadiazine (Re-Balance) are all FDA-approved treatments for EPM in horses.

Question 129: A cat presents with a ventromedial corneal opacity that appears yellow-brown and is firmly adherent to the cornea. There is no fluorescein stain uptake. What is the most likely diagnosis?

Indolent corneal ulcer
Eosinophilic keratitis
Anterior lens luxation
Corneal sequestrum (corneal nigrum) (Correct answer)

Correct answer: Corneal sequestrum (corneal nigrum)

Corneal sequestrum (also called corneal nigrum or corneal mummification) is unique to cats and is characterized by a focal area of corneal stromal necrosis that appears amber, brown, or black. It does not stain with fluorescein (no epithelial defect initially) and is firmly embedded in the stroma. It is most common in brachycephalic breeds. Treatment is surgical keratectomy. Eosinophilic keratitis has a white/pink vascularized plaque appearance; indolent ulcers have loose epithelial edges and do stain.

Question 130: A stallion undergoes a breeding soundness evaluation. His total sperm output per ejaculate is 12 × 10⁹, with 65% progressive motility and 62% morphologically normal spermatozoa. Using the minimum BSE criteria for stallions, what is the calculated minimum number of progressively motile morphologically normal spermatozoa (PMMN) per ejaculate, and does this stallion pass or fail?

PMMN = 4.84 × 10⁹; the stallion fails because the morphology is below the 70% minimum even though motility is adequate
PMMN = 7.8 × 10⁹; the stallion passes all three parameters independently without needing a composite calculation
PMMN = 4.84 × 10⁹; the stallion passes since this exceeds the threshold of 1 × 10⁹ (Correct answer)
PMMN = 4.84 × 10⁹; the stallion conditionally passes pending a second ejaculate evaluation within 1 hour

Correct answer: PMMN = 4.84 × 10⁹; the stallion passes since this exceeds the threshold of 1 × 10⁹

PMMN = Total sperm × %progressive motility × %normal morphology = 12 × 10⁹ × 0.65 × 0.62 = 4.836 × 10⁹. The minimum PMMN threshold for an 'adequate' classification in equine BSE is 1 × 10⁹ PMMN per ejaculate (some references cite 500 × 10⁶ as the absolute floor). With ~4.84 × 10⁹ PMMN, this stallion exceeds the threshold. While morphology at 62% is below the often-cited guideline of ≥70% morphologically normal, BSE classification in the stallion is primarily composite-score driven (PMMN) rather than requiring each parameter to independently reach a threshold — so the stallion passes on the composite metric. The conditional second ejaculate is not indicated when the first ejaculate result is clearly above threshold.

Question 131: A renal biopsy from a 32-year-old man with hematuria and proteinuria shows mesangial hypercellularity with IgA and C3 deposits on immunofluorescence. Electron microscopy reveals predominantly mesangial electron-dense deposits. Three months after an upper respiratory infection, his serum complement levels are checked: C3 is normal, C4 is normal. Which mechanism best explains preserved complement levels in this disease?

Immune complex formation triggering classical pathway with rapid C3 convertase decay
Properdin-mediated amplification loop selectively consuming C3 without affecting C4
Activation of the lectin complement pathway with sparing of C4 consumption (Correct answer)
Activation of the alternative complement pathway with regulatory factor H deficiency

Correct answer: Activation of the lectin complement pathway with sparing of C4 consumption

IgA nephropathy (Berger disease) activates primarily the lectin pathway (via mannose-binding lectin recognizing galactose-deficient IgA1) and the alternative pathway. Both bypass C1q and C4, meaning C4 is not consumed. C3 can also remain normal in many patients because the complement activation is focal or adequately regulated. The classical pathway (C1q→C4→C2→C3) would reduce both C3 and C4, as seen in lupus nephritis or membranoproliferative GN type I. Preserved C4 with normal or near-normal C3 is a key distinguishing feature of IgA nephropathy.

Question 132: Lead poisoning in children is most associated with which neurological sequela?

Acute hemorrhagic encephalitis
Cognitive impairment and reduced IQ (Correct answer)
Sensorineural hearing loss
Spastic diplegia of lower extremities

Correct answer: Cognitive impairment and reduced IQ

Chronic low-level lead exposure in children disrupts synaptic development and calcium-mediated neurotransmitter release, causing irreversible cognitive deficits and reduced IQ.

Question 133: Which of the following sets of clinical pathology findings is most consistent with a diagnosis of disseminated intravascular coagulation (DIC)?

Increased platelet count, prolonged PT, prolonged aPTT, decreased FDPs
Normal platelet count, normal PT, normal aPTT, elevated FDPs
Thrombocytopenia, prolonged PT, prolonged aPTT, elevated FDPs (Correct answer)
Thrombocytopenia, shortened PT, shortened aPTT, normal FDPs

Correct answer: Thrombocytopenia, prolonged PT, prolonged aPTT, elevated FDPs

Disseminated intravascular coagulation (DIC) is a complex syndrome of systemic, uncontrolled activation of coagulation. This leads to widespread microthrombi formation, consuming platelets and coagulation factors, which results in thrombocytopenia and prolongation of clotting times (PT and aPTT). Simultaneously, the fibrinolytic system is activated to break down clots, leading to an increase in fibrin degradation products (FDPs).

Question 134: Which organism is the most common cause of contagious equine metritis (CEM)?

Streptococcus zooepidemicus
Klebsiella pneumoniae
Pseudomonas aeruginosa
Taylorella equigenitalis (Correct answer)

Correct answer: Taylorella equigenitalis

Taylorella equigenitalis is the gram-negative obligate pathogen responsible for CEM, a reportable venereal disease causing endometritis and reduced fertility in mares.

Question 135: A 10-year-old, obese West Highland White Terrier is presented for a chronic, harsh cough that has been present for over two months. Physical examination is unremarkable except for the cough elicited on tracheal palpation. Thoracic radiographs are taken. Which of the following radiographic findings would be most consistent with a diagnosis of chronic bronchitis?

A lobar alveolar pattern with air bronchograms
A diffuse, unstructured interstitial pattern
Pleural effusion and cardiomegaly
A prominent bronchial pattern (doughnuts and tram lines) (Correct answer)

Correct answer: A prominent bronchial pattern (doughnuts and tram lines)

The classic radiographic finding in canine chronic bronchitis is a prominent bronchial pattern. This is caused by inflammation and thickening of the bronchial walls, which appear as 'doughnuts' when viewed on-end and 'tram lines' when viewed in parallel with the x-ray beam. While other patterns can coexist, the bronchial pattern is the most characteristic feature.

Question 136: In rheumatoid arthritis, which of the following is the main site of inflammation?

Tendons
Articular cartilage
Synovium (Correct answer)
Bone marrow

Correct answer: Synovium

The main cause of rheumatoid arthritis is inflammation of the synovium, which can result in synovial hyperplasia and the eventual decomposition of bone and cartilage.

Question 137: The 'gold standard' for diagnosing rabies in animals involves which laboratory technique on which tissue?

ELISA on serum
Virus isolation from saliva
Direct fluorescent antibody (DFA) test on fresh brain tissue (brainstem/cerebellum) (Correct answer)
Immunohistochemistry on formalin-fixed skin

Correct answer: Direct fluorescent antibody (DFA) test on fresh brain tissue (brainstem/cerebellum)

The DFA test on unfixed brain tissue, particularly the brainstem and cerebellum, is the CDC-approved gold standard for animal rabies diagnosis.

Question 138: Which of the following statements most accurately describes a key physiological difference between the avian and mammalian respiratory systems?

Gas exchange in mammals occurs primarily in structures called parabronchi.
Birds have a unidirectional flow of air through their lungs, facilitated by air sacs. (Correct answer)
Avian lungs are highly elastic and expand significantly during inspiration.
Mammals utilize a crosscurrent exchange system for maximum oxygen uptake.

Correct answer: Birds have a unidirectional flow of air through their lungs, facilitated by air sacs.

The avian respiratory system is unique in that it features a unidirectional flow of air through rigid lungs, a process made possible by a system of air sacs. This allows for continuous gas exchange during both inspiration and expiration. In contrast, mammals have tidal airflow (in and out) in elastic lungs where gas exchange occurs in alveoli, not parabronchi. The crosscurrent exchange system is characteristic of birds, not mammals.

Question 139: Which waterborne disease is most associated with groundwater contamination from agricultural runoff containing nitrates?

Cryptosporidiosis
Methemoglobinemia (blue baby syndrome) (Correct answer)
Hepatitis A
Fluorosis

Correct answer: Methemoglobinemia (blue baby syndrome)

High nitrate levels in drinking water cause methemoglobinemia in infants, reducing blood oxygen-carrying capacity.

Question 140: A clinical nutritionist is optimizing protein delivery for a mechanically ventilated patient with acute kidney injury (AKI) NOT on renal replacement therapy (RRT), with a measured GFR of 18 mL/min. Current ASPEN/SCCM guidelines for this specific scenario recommend:

Moderate protein delivery of 1.2–1.5 g/kg/day, with reassessment if RRT is initiated, at which point protein should increase to 1.5–2.5 g/kg/day (Correct answer)
Protein restriction to 0.6–0.8 g/kg/day to reduce BUN accumulation and delay initiation of RRT
Protein-free enteral nutrition until creatinine stabilizes, with lipid emulsion as the primary non-protein energy source
Standard high-protein delivery of 1.5–2.0 g/kg/day, identical to non-AKI ICU patients, because catabolism overrides renal concerns

Correct answer: Moderate protein delivery of 1.2–1.5 g/kg/day, with reassessment if RRT is initiated, at which point protein should increase to 1.5–2.5 g/kg/day

ASPEN/SCCM guidelines distinguish AKI-without-RRT from AKI-on-RRT. For non-RRT AKI in the ICU, protein should not be severely restricted (restriction does not meaningfully delay RRT initiation and worsens catabolism), but full high-protein delivery used for septic or other ICU patients is also not recommended due to uremic solute accumulation. The evidence-supported approach is moderate protein (≈1.2–1.5 g/kg/day) with upward titration to 1.5–2.5 g/kg once continuous RRT begins, since dialysis itself removes amino acids and increases protein requirements. Protein-free nutrition is never guideline-recommended in ICU patients with AKI.

Question 141: Which muscle is responsible for abduction of the vocal cords?

Lateral cricoarytenoid
Thyroarytenoid
Cricothyroid
Posterior cricoarytenoid (Correct answer)

Correct answer: Posterior cricoarytenoid

The posterior cricoarytenoid is the only intrinsic laryngeal muscle that abducts the vocal cords by rotating the arytenoids laterally.

Question 142: A 6-year-old cat is presented 4 hours after being bitten by a dog. The wound is a 3 cm puncture on the thorax with minimal gross contamination. The surgeon plans to lavage, debride the wound edges, and perform primary closure. How would this wound be classified?

Contaminated
Clean-contaminated (Correct answer)
Clean
Dirty or infected

Correct answer: Clean-contaminated

A clean-contaminated wound is a surgical wound where the respiratory, gastrointestinal, or urogenital tracts are entered under controlled conditions, or a traumatic wound that is recent (less than 6 hours old) and has minimal contamination. Since this is a fresh bite wound, it falls into the clean-contaminated category. A 'clean' wound is a non-traumatic, uninfected surgical incision. A 'contaminated' wound is an open, fresh, accidental wound, or a surgical wound with a major break in sterile technique. A 'dirty' wound is an old traumatic wound with retained devitalized tissue and shows signs of infection.

Question 143: A patient develops masseter muscle rigidity immediately after succinylcholine administration. What is the most concerning diagnosis?

Laryngospasm
Normal fasciculation response
Pseudocholinesterase deficiency
Malignant hyperthermia susceptibility (Correct answer)

Correct answer: Malignant hyperthermia susceptibility

Masseter spasm after succinylcholine is a warning sign of malignant hyperthermia susceptibility and warrants discontinuation of triggering agents.

Question 144: Which mechanism underlies the teratogenicity of thalidomide?

Inhibition of cereblon-mediated degradation of transcription factors required for limb development (Correct answer)
Folate antagonism impairing neural tube closure
Androgen receptor blockade disrupting genital development
Direct alkylation of embryonic DNA causing strand breaks

Correct answer: Inhibition of cereblon-mediated degradation of transcription factors required for limb development

Thalidomide binds cereblon (CRBN), diverting its E3 ubiquitin ligase activity to degrade transcription factors such as SALL4 that are essential for limb and organ development.

Question 145: Under the USDA Animal Welfare Act regulations, which of the following species is explicitly EXCLUDED from the definition of 'animal' for purposes of coverage, even when used in biomedical research?

Oryctolagus cuniculus (rabbits) in dermal toxicity testing
Mustela putorius furo (ferrets) used in influenza studies
Macaca mulatta (rhesus macaques) in cognitive neuroscience
Mus musculus (laboratory mice) bred for research (Correct answer)

Correct answer: Mus musculus (laboratory mice) bred for research

The U.S. Animal Welfare Act (AWA) explicitly excludes birds, rats of the genus Rattus, and mice of the genus Mus bred for use in research from its definition of 'animal' under 7 U.S.C. § 2132(g). This exclusion, formalized in 2002 via the Farm Security and Rural Investment Act amendment, means laboratory mice (Mus musculus) bred for research receive no federal AWA protections. Ferrets, rhesus macaques, and rabbits are all covered AWA species.

Question 146: Left displacement of the abomasum (LDA) in dairy cows most commonly occurs in which time period relative to calving?

3–6 months postpartum
Last 2 weeks of gestation
First 6 weeks postpartum (Correct answer)
Mid-lactation (6–9 months)

Correct answer: First 6 weeks postpartum

LDA occurs most commonly in the first 6 weeks after calving when the rumen contracts post-partum, leaving space for the gas-filled abomasum to displace leftward.

Question 147: Which structure is at greatest risk when the long thoracic nerve is damaged?

Pectoralis major
Serratus anterior (Correct answer)
Rhomboids
Subscapularis

Correct answer: Serratus anterior

The long thoracic nerve innervates the serratus anterior; its damage causes winging of the scapula because the muscle can no longer hold the scapula against the thoracic wall.

Question 148: A 4-year-old captive chimpanzee repeatedly rocks back and forth, self-grasps, and displays pica behavior. These stereotypies most likely indicate which underlying welfare concern?

Dominance-asserting displacement behavior directed at subordinate group members
Chronic psychological stress due to inadequate environmental enrichment and social deprivation (Correct answer)
Normal developmental behavior associated with adolescent cognitive restructuring
Subclinical viral encephalitis causing basal ganglia dysfunction

Correct answer: Chronic psychological stress due to inadequate environmental enrichment and social deprivation

Stereotypies in non-human primates—repetitive, invariant behaviors with no apparent function—are hallmark indicators of chronic psychological stress, typically arising from inadequate environmental complexity, social isolation, or early maternal deprivation. Rocking, self-grasping, and pica are classic examples documented extensively in deprived laboratory and zoo primates. Viral encephalitis would present with additional neurological signs, and stereotypies are not considered normal developmental behavior.

Question 149: Which virus causes Marek's disease in poultry and belongs to which family?

Newcastle disease virus, family Paramyxoviridae
Gallid herpesvirus 2, family Herpesviridae (Correct answer)
Avian leukosis virus, family Retroviridae
Infectious bursal disease virus, family Birnaviridae

Correct answer: Gallid herpesvirus 2, family Herpesviridae

Marek's disease is caused by Gallid herpesvirus 2 (a cell-associated alphaherpesvirus), which induces T-cell lymphomas in susceptible chickens.

Question 150: Which muscle is involved in forearm flexion?

Triceps brachii
Biceps brachii (Correct answer)
Deltoid
Brachialis

Correct answer: Biceps brachii

A strong forearm flexor at the elbow joint is the biceps brachii.

Question 151: Which RNA virus causes foot-and-mouth disease (FMD), and why is it significant to the US livestock industry?

Aphthovirus (Picornaviridae); FMD is a foreign animal disease that would cause massive trade embargoes if introduced (Correct answer)
Orbivirus (Reoviridae); it affects only swine
Vesiculovirus (Rhabdoviridae); it is endemic in the US Midwest
Arterivirus (Arteriviridae); it is controlled by routine vaccination

Correct answer: Aphthovirus (Picornaviridae); FMD is a foreign animal disease that would cause massive trade embargoes if introduced

FMD is caused by Aphthovirus (family Picornaviridae) and is a reportable foreign animal disease whose introduction would immediately halt US livestock exports.

Question 152: Environmental enrichment for non-human primates in research settings primarily serves to:

Promote species-typical behavior and reduce psychological distress (Correct answer)
Increase caloric intake
Reduce aggression between technicians and animals
Simplify husbandry procedures

Correct answer: Promote species-typical behavior and reduce psychological distress

Enrichment provides cognitive stimulation and social outlets that allow expression of species-typical behaviors, directly improving psychological welfare.

Question 153: Dermatophytosis in cats is most commonly caused by which organism?

Trichophyton mentagrophytes
Candida albicans
Microsporum canis (Correct answer)
Microsporum gypseum

Correct answer: Microsporum canis

Microsporum canis accounts for approximately 90% of feline dermatophytosis cases and fluoresces apple-green under a Wood's lamp.

Question 154: During a posterior approach to the hip, the surgeon identifies the short external rotators. Which of the following muscles is MOST superior in the anatomical layering of this group, lying directly beneath the gluteus minimus?

Quadratus femoris
Obturator internus
Piriformis (Correct answer)
Superior gemellus

Correct answer: Piriformis

The piriformis is the most superior of the short external rotators of the hip, lying immediately deep to the gluteus minimus and exiting the pelvis through the greater sciatic foramen. The order from superior to inferior is: piriformis, superior gemellus, obturator internus tendon, inferior gemellus, and quadratus femoris. The piriformis serves as the key surgical landmark in posterior hip approaches and its relationship to the sciatic nerve is clinically critical.

Question 155: The amino acid taurine is conditionally essential in cats primarily because cats have limited ability to do which of the following?

Recycle taurine from bile acids
Synthesize taurine from cysteine due to low cysteine sulfinic acid decarboxylase activity (Correct answer)
Absorb taurine from the small intestine
Convert methionine to cysteine

Correct answer: Synthesize taurine from cysteine due to low cysteine sulfinic acid decarboxylase activity

Cats have very low hepatic cysteine sulfinic acid decarboxylase activity, severely limiting endogenous taurine synthesis from cysteine.

Question 156: Ammonia toxicity in ruminants fed high non-protein nitrogen (NPN) diets occurs because excess ammonia overwhelms the liver's ability to convert it to urea via the urea cycle. Which enzyme catalyzes the rate-limiting, first committed step of the urea cycle?

Arginase
Argininosuccinate lyase
Carbamoyl phosphate synthetase I (CPS I) (Correct answer)
Ornithine transcarbamylase

Correct answer: Carbamoyl phosphate synthetase I (CPS I)

Carbamoyl phosphate synthetase I (CPS I), located in the mitochondrial matrix, catalyzes the ATP-dependent conversion of ammonia + CO2 → carbamoyl phosphate. This is the rate-limiting step of the hepatic urea cycle and is allosterically activated by N-acetylglutamate. When ammonia influx exceeds CPS I capacity (as with rumen NPN overload), blood ammonia rises, causing neurological signs.

Question 157: Which part of the equine foot corresponds anatomically to the human fingernail?

Frog
Sole
Hoof wall (Correct answer)
White line

Correct answer: Hoof wall

The hoof wall is the cornified epidermal structure that is the anatomical homolog of the human fingernail, produced by the coronary band.

Question 158: A patient with severe hepatic cirrhosis (Child-Pugh Class C) requires emergency laparotomy. Which neuromuscular blocking agent is most appropriate, and why?

Vecuronium, because it has the shortest duration of action
Pancuronium, because it is renally cleared and avoids hepatic metabolism
Cisatracurium, because it undergoes Hofmann elimination independent of hepatic function (Correct answer)
Rocuronium, because its rapid onset allows RSI without succinylcholine

Correct answer: Cisatracurium, because it undergoes Hofmann elimination independent of hepatic function

Cisatracurium undergoes Hofmann elimination — a spontaneous, pH- and temperature-dependent chemical degradation — that is completely independent of hepatic or renal function. This makes it the safest choice in severe liver failure. Rocuronium and vecuronium rely heavily on biliary/hepatic clearance and have markedly prolonged duration in Child-Pugh C patients. Pancuronium is partially renally cleared but also has significant hepatic metabolism; it also has cardiovascular side effects making it unsuitable for emergency cases.

Question 159: During oxidative phosphorylation, uncoupling agents such as 2,4-dinitrophenol (DNP) cause hyperthermia by:

Dissipating the proton gradient across the inner mitochondrial membrane as heat without synthesizing ATP (Correct answer)
Inhibiting substrate-level phosphorylation in the TCA cycle
Blocking electron transfer at Complex III
Directly inhibiting ATP synthase, halting ATP production

Correct answer: Dissipating the proton gradient across the inner mitochondrial membrane as heat without synthesizing ATP

Uncouplers are lipophilic weak acids that shuttle protons across the inner mitochondrial membrane, bypassing ATP synthase. The energy stored in the proton-motive force is released as heat rather than captured as ATP. Electron transport continues (and may accelerate), but ATP synthesis is uncoupled. This explains hyperthermia and cellular energy depletion seen in DNP poisoning and in conditions involving endogenous uncoupling proteins (thermogenesis in brown adipose tissue).

Question 160: Which serologic test is used as the official screening test for brucellosis in US cattle?

Complement fixation test only
Milk ring test only
Rose Bengal plate test (RBPT) or buffered Brucella antigen test (Correct answer)
PCR on whole blood

Correct answer: Rose Bengal plate test (RBPT) or buffered Brucella antigen test

The buffered Brucella antigen (Rose Bengal plate) test is the official US screening test for bovine brucellosis in the national eradication program.

Question 161: Which mechanism allows methicillin-resistant Staphylococcus aureus (MRSA) to resist beta-lactam antibiotics?

Production of beta-lactamase that hydrolyzes all beta-lactams
Production of an altered penicillin-binding protein (PBP2a) encoded by the mecA gene (Correct answer)
Reduced outer membrane permeability
Efflux pump expelling all beta-lactams

Correct answer: Production of an altered penicillin-binding protein (PBP2a) encoded by the mecA gene

MRSA carries the mecA gene encoding PBP2a, a transpeptidase with very low affinity for all beta-lactam antibiotics, conferring broad resistance.

Question 162: When performing a welfare assessment using the Welfare Quality protocol for cattle, observers score animals on how many principles?

Three principles: health, behavior, and environment
Four principles: good feeding, good housing, good health, and appropriate behavior (Correct answer)
Two principles: physical and psychological welfare
Five principles including reproductive performance

Correct answer: Four principles: good feeding, good housing, good health, and appropriate behavior

The Welfare Quality protocol organizes cattle welfare into four principles (feeding, housing, health, behavior), each containing multiple measurable criteria scored at the animal level.

Question 163: Hypophosphatemia in postparturient dairy cows is most commonly associated with which condition?

Hardware disease
Grass tetany
Downer cow syndrome following hypocalcemia (milk fever) (Correct answer)
Bloat

Correct answer: Downer cow syndrome following hypocalcemia (milk fever)

Severe hypophosphatemia is a common sequela to milk fever and contributes to recumbency by impairing ATP production needed for muscle contraction.

Question 164: A 34-year-old woman presents with a thyroid nodule. FNA cytology demonstrates a follicular patterned lesion with nuclear features including irregular nuclear contours, nuclear grooves, and occasional intranuclear pseudoinclusions in approximately 30% of cells; the remainder show bland follicular cells. The lesion is encapsulated with a thick fibrous capsule and no capsular or vascular invasion on excision. What is the most appropriate classification?

Classic papillary thyroid carcinoma, encapsulated variant
Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) (Correct answer)
Follicular carcinoma, minimally invasive
Follicular adenoma with focal papillary architecture

Correct answer: Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)

NIFTP requires: (1) encapsulation or clear demarcation, (2) follicular growth pattern (≤1% papillae, no psammoma bodies, no well-formed papillae), (3) papillary-like nuclear features (nuclear score ≥2), and (4) NO capsular or vascular invasion. This lesion meets all criteria. Papillary carcinoma requires invasion or unambiguous papillary architecture. Follicular adenoma lacks the nuclear features. Minimally invasive follicular carcinoma requires capsular/vascular invasion.

Question 165: When performing a towel clamp placement for surgical draping, what is the primary purpose of securing the drape to the patient's skin?

To facilitate tissue retraction
To improve hemostasis at the skin edge
To mark the incision site
To prevent drape slippage and contamination of the sterile field (Correct answer)

Correct answer: To prevent drape slippage and contamination of the sterile field

Towel clamps anchor the drapes to the patient to prevent movement that could expose non-sterile surfaces and contaminate the operative field.

Question 166: A 25-year-old male presents with a mediastinal mass. Biopsy shows large cells with bilobed nuclei and prominent eosinophilic 'owl-eye' nucleoli in a background of lymphocytes, eosinophils, and plasma cells. What is the diagnosis?

Nodular sclerosis Hodgkin lymphoma (Correct answer)
Diffuse large B-cell lymphoma
T-lymphoblastic lymphoma
Primary mediastinal large B-cell lymphoma

Correct answer: Nodular sclerosis Hodgkin lymphoma

Reed-Sternberg cells with owl-eye nucleoli in an inflammatory background define classical Hodgkin lymphoma, with nodular sclerosis being most common in young adults with mediastinal involvement.

Question 167: A heavily pregnant cow is found in lateral recumbency and unable to rise. She is alert but unable to stand despite calcium treatment. Her selenium and vitamin E levels are low. What condition should be considered?

Grass tetany (hypomagnesemia)
Downer cow syndrome with sciatic nerve damage
White muscle disease (nutritional myodegeneration) (Correct answer)
Transit tetany (transport hypocalcemia)

Correct answer: White muscle disease (nutritional myodegeneration)

White muscle disease from selenium/vitamin E deficiency causes myodegeneration that may present as recumbency in adult cattle; treatment with selenium and vitamin E supplementation is indicated.

Question 168: A patient develops tachycardia, hyperthermia, muscle rigidity, and rhabdomyolysis after sevoflurane exposure. Temperature is 41°C. What is the immediate treatment?

Cool the patient with ice packs and reassess
Increase volatile anesthetic concentration to deepen anesthesia
Administer beta-blockers for tachycardia control
Administer dantrolene 2.5 mg/kg IV immediately (Correct answer)

Correct answer: Administer dantrolene 2.5 mg/kg IV immediately

Malignant hyperthermia requires immediate dantrolene (2.5 mg/kg IV, repeat up to 10 mg/kg), discontinuation of triggers, and aggressive cooling.

Question 169: When closing a ventral midline celiotomy in a dog, which of the following suture materials and patterns carries the highest evidence-based risk of incisional hernia in the immediate postoperative period?

Polydioxanone (PDS II) in a simple interrupted pattern at the external rectus sheath
Poliglecaprone 25 (Monocryl) in a simple continuous pattern closing the linea alba
Polyglactin 910 (Vicryl) in a simple continuous pattern closing the linea alba (Correct answer)
Nylon (Ethilon) in a figure-of-eight pattern at the external rectus sheath

Correct answer: Polyglactin 910 (Vicryl) in a simple continuous pattern closing the linea alba

Polyglactin 910 (Vicryl) is a braided, rapidly absorbed suture that loses approximately 50% of its tensile strength by 2–3 weeks postoperatively and is essentially completely absorbed by 60–90 days. Used in a continuous pattern for linea alba closure, early tensile strength loss — especially in patients with delayed healing (hypoalbuminemia, corticosteroid use, obesity) — significantly increases incisional hernia risk before adequate fibrous union has occurred. Polydioxanone retains strength longer (~70% at 2 weeks, ~50% at 4 weeks). Poliglecaprone 25 retains ~50–60% at 1 week and ~20–30% at 2 weeks — also a concern, but PDS is the gold standard for linea closure precisely because of its prolonged retention. Nylon is non-absorbable and maintains strength indefinitely.

Question 170: In canine autoimmune hemolytic anemia (AIHA), erythrocyte destruction occurs primarily via which mechanism?

Type IV hypersensitivity cytotoxic T-cell attack on erythrocytes
Type I hypersensitivity degranulation of basophils
Type II hypersensitivity — IgG/IgM antibodies against RBC surface antigens leading to complement lysis and phagocytosis (Correct answer)
Type III hypersensitivity immune complex deposition in splenic sinusoids

Correct answer: Type II hypersensitivity — IgG/IgM antibodies against RBC surface antigens leading to complement lysis and phagocytosis

AIHA is a classic Type II hypersensitivity. Auto-antibodies (typically IgG) bind erythrocyte surface antigens; IgM can also fix complement directly. Opsonized RBCs are phagocytosed by splenic and hepatic macrophages (extravascular hemolysis) or lysed by the membrane attack complex (intravascular hemolysis). Spherocytes on blood smear and a positive Coombs test are hallmarks.

Question 171: A 70-year-old male has a serum PSA of 18 ng/mL. Prostate biopsy reveals glands lined by a single layer of cells with no basal cell layer. Gleason grading is used. What does a combined Gleason score of 7 (3+4) indicate?

Low-grade carcinoma with a favorable prognosis
Intermediate-grade carcinoma with predominantly well-formed glands (Correct answer)
Benign prostatic hyperplasia
High-grade carcinoma with predominantly poorly formed glands

Correct answer: Intermediate-grade carcinoma with predominantly well-formed glands

Gleason 3+4=7 indicates intermediate grade with the dominant pattern being grade 3 (well-formed glands) and secondary pattern grade 4 (poorly formed glands).

Question 172: An outbreak of gastrointestinal illness occurs among attendees of a large catered event. Public health officials interview a group of people who became ill (cases) and a group of attendees who remained healthy (controls) to compare their food consumption history and identify the likely source. Which epidemiological study design does this represent?

Case-control study (Correct answer)
Randomized controlled trial
Cross-sectional study
Prospective cohort study

Correct answer: Case-control study

A case-control study is a retrospective study that starts by identifying individuals with the disease or outcome of interest (cases) and a suitable control group without the outcome. It then looks back in time to compare the frequency of exposure to a risk factor in both groups. This method is efficient for outbreak investigations where the goal is to find the source after the fact.

Question 173: The therapeutic effect of benzodiazepines in anxiety disorders is mediated by:

Potentiating GABA-A receptor chloride ion channel opening frequency (Correct answer)
Inhibiting serotonin reuptake at presynaptic terminals
Directly activating GABA-B receptors and inhibiting calcium channels
Blocking NMDA glutamate receptors

Correct answer: Potentiating GABA-A receptor chloride ion channel opening frequency

Benzodiazepines bind allosterically to GABA-A receptors, increasing the frequency of chloride channel opening in response to GABA and enhancing inhibitory neurotransmission.

Question 174: A 6-month-old Holstein calf in a herd in the midwest presents with profuse watery diarrhea, dehydration, and metabolic acidosis. Cryptosporidium parvum oocysts are identified on Ziehl-Neelsen staining of fecal smears. Which property of C. parvum makes it uniquely resistant to standard water chlorination protocols?

Sporozoite sequestration within a parasitophorous vacuole resistant to oxidizing agents
Thick two-layered oocyst wall with sporulation occurring prior to shedding (Correct answer)
Ability to form autoinfective thin-walled oocysts that reinvade the host intestine
Intracellular but extracytoplasmic development within enterocyte brush border

Correct answer: Thick two-layered oocyst wall with sporulation occurring prior to shedding

C. parvum oocysts are immediately infective when shed (sporulated) and possess a thick, two-layered wall that renders them highly resistant to chlorine-based disinfectants at concentrations used in municipal water systems. This is why filtration rather than chlorination is the primary water treatment strategy. The extracytoplasmic location is a biologically interesting feature but is not the reason for chlorine resistance.

Question 175: A 58-year-old man undergoes resection of a colonic mass. Histology shows a serrated adenocarcinoma with loss of MLH1 and PMS2 by immunohistochemistry, but MSI-PCR shows microsatellite stability (MSS). Which of the following best explains this discordant finding?

Germline MLH1 mutation with a second somatic hit causing heterogeneous protein expression
Technical artifact from prolonged formalin fixation degrading MLH1 protein epitopes
MLH1/PMS2 loss due to post-translational ubiquitination without gene silencing
Somatic BRAF V600E mutation causing MLH1 promoter hypermethylation with incomplete protein loss (Correct answer)

Correct answer: Somatic BRAF V600E mutation causing MLH1 promoter hypermethylation with incomplete protein loss

BRAF V600E-driven MLH1 promoter hypermethylation can result in partial or heterogeneous MLH1/PMS2 protein loss on IHC while PCR-based MSI testing remains stable if sufficient mismatch repair capacity persists or if only a subclone is affected. This IHC/MSI discordance is a recognized pitfall in Lynch syndrome screening; BRAF mutation testing and MLH1 methylation analysis are the appropriate next steps.

Question 176: Which of the following correctly pairs a toxin with its specific antidote mechanism?

Digoxin toxicity → Glucagon activates adenylyl cyclase, bypassing the blocked Na⁺/K⁺-ATPase
Cyanide poisoning → Deferoxamine chelates cyanide ions and promotes urinary excretion
Methanol poisoning → Fomepizole competitively inhibits alcohol dehydrogenase, preventing formate accumulation (Correct answer)
Organophosphate poisoning → N-acetylcysteine replenishes acetylcholinesterase at nerve terminals

Correct answer: Methanol poisoning → Fomepizole competitively inhibits alcohol dehydrogenase, preventing formate accumulation

Fomepizole (4-methylpyrazole) is a competitive inhibitor of alcohol dehydrogenase (ADH). In methanol poisoning, ADH converts methanol to formaldehyde and then formate, which causes the metabolic acidosis and optic nerve toxicity. By blocking ADH, fomepizole prevents this conversion. Glucagon bypasses β-blockade, not digoxin toxicity (that uses Fab fragments). Pralidoxime, not N-acetylcysteine, reactivates acetylcholinesterase. Cyanide poisoning is treated with hydroxocobalamin or nitrites/thiosulfate, not deferoxamine (which is used for iron toxicity).

Question 177: An MRI brain with gadolinium shows a ring-enhancing lesion at the gray-white matter junction in an immunocompetent 45-year-old with new-onset seizures. Diffusion-weighted imaging (DWI) demonstrates restricted diffusion within the ring. Which diagnosis does this DWI pattern MOST favor compared to a lesion with facilitated diffusion in the center?

High-grade glioblastoma multiforme with central necrosis
Metastatic adenocarcinoma with hemorrhagic core
Pyogenic brain abscess with pus in the core (Correct answer)
Tumefactive multiple sclerosis with incomplete ring enhancement

Correct answer: Pyogenic brain abscess with pus in the core

Restricted diffusion (high signal on DWI, low ADC) within the center of a ring-enhancing lesion is the imaging hallmark of a pyogenic brain abscess. The thick pus contains densely packed bacteria, inflammatory cells, and necrotic debris that restrict water molecule movement. High-grade gliomas and metastases typically show facilitated diffusion (high ADC) in their necrotic cores because liquefactive necrosis allows free water movement. This DWI pattern is a critical discriminator that can prevent unnecessary biopsy of an infectious lesion in an otherwise immunocompetent host.

Question 178: A state health department is evaluating whether to implement a mandatory iodine fortification program for table salt to address subclinical iodine deficiency (median urinary iodine 85 µg/L) in a population where 22% of pregnant women have iodine levels below 50 µg/L. An independent assessment finds that the current voluntary fortification program covers only 40% of salt sold. Using the PRECEDE-PROCEED model, which phase is being addressed by quantifying the urinary iodine levels and pregnancy-specific burden, and what is the MOST critical barrier to address next?

Administrative assessment phase; the critical barrier is policy factors, specifically lack of legislative authority for mandatory fortification
Epidemiological assessment phase; the most critical barrier is enabling factors — specifically, the inadequate market penetration of voluntarily fortified salt (Correct answer)
Behavioral assessment phase; the critical barrier is predisposing factors, specifically consumer knowledge deficits about iodine
Social assessment phase; the critical barrier is reinforcing factors, specifically inadequate clinician counseling about iodine supplementation

Correct answer: Epidemiological assessment phase; the most critical barrier is enabling factors — specifically, the inadequate market penetration of voluntarily fortified salt

In the PRECEDE-PROCEED model, quantifying disease burden and at-risk subgroups (median urinary iodine, % of pregnant women deficient) constitutes the Epidemiological Assessment phase (Phase 2). The data show that voluntary fortification reaches only 40% of salt — this is an enabling factor (availability and accessibility of the health-promoting product), not a knowledge deficit or policy gap. Enabling factors are environmental and resource conditions that make healthy behavior possible. The most actionable next step — shifting to mandatory fortification or dramatically expanding distribution — directly targets this enabling barrier. Predisposing (knowledge/attitudes) and reinforcing (social support/clinician counseling) factors are secondary when product availability itself is the bottleneck.

Question 179: A transbronchial biopsy from a lung transplant recipient at 8 months post-transplant shows perivascular lymphocytic infiltrates grading A2, fibrous obliteration of small airways with eccentric submucosal fibrosis, and loss of bronchiolar epithelium. No viral cytopathic changes are identified. CMV PCR is undetectable. What pathologic process is MOST likely responsible for this biopsy pattern, and what is its significance?

Obliterative bronchiolitis (chronic lung allograft dysfunction); it represents the dominant cause of late post-transplant mortality (Correct answer)
Lymphocytic bronchiolitis without fibrous obliteration; typically resolves without intervention
Post-transplant lymphoproliferative disorder; requires reduction of immunosuppression and anti-CD20 therapy
Acute cellular rejection grade A2; treatment with pulse steroids is curative in >90% of cases

Correct answer: Obliterative bronchiolitis (chronic lung allograft dysfunction); it represents the dominant cause of late post-transplant mortality

The combination of perivascular A2 rejection with fibrous obliteration of small airways and loss of bronchiolar epithelium — in the absence of viral infection — is consistent with obliterative bronchiolitis (OB), the histologic correlate of bronchiolitis obliterans syndrome (BOS), the leading cause of death in long-term lung transplant survivors. Unlike acute rejection, OB is poorly reversible with steroids and portends progressive allograft loss. PTLD would show atypical lymphoid proliferations, often EBV-driven, with mass-like lesions.

Question 180: A pharmacokineticist notes that Drug X has a hepatic extraction ratio of 0.95. A patient with hepatic cirrhosis and portosystemic shunting starts this drug orally. Compared to a healthy subject receiving the same dose, what is the primary pharmacokinetic change expected?

Prolonged half-life due to decreased renal clearance secondary to hepatorenal syndrome
Decreased AUC due to increased gastrointestinal motility associated with liver disease
Markedly increased oral bioavailability due to bypassed first-pass hepatic metabolism (Correct answer)
Reduced volume of distribution due to decreased plasma protein binding

Correct answer: Markedly increased oral bioavailability due to bypassed first-pass hepatic metabolism

A hepatic extraction ratio of 0.95 means 95% of an orally administered drug is removed during first-pass hepatic metabolism in a healthy individual, leaving only ~5% bioavailable. In cirrhosis with portosystemic shunts, portal blood bypasses the liver entirely and enters systemic circulation directly. This eliminates first-pass metabolism for that shunted fraction, dramatically increasing bioavailability. Classic high-extraction drugs include propranolol, lidocaine, morphine, and labetalol — their oral doses must be significantly reduced in cirrhotic patients to avoid toxicity.

Question 181: A 7-year-old intact male Shetland Sheepdog presents with PU/PD, bilateral symmetric alopecia, and muscle wasting. Baseline cortisol is 2.1 µg/dL. An ACTH stimulation test yields a post-stimulation cortisol of 24.3 µg/dL. Abdominal ultrasound reveals bilaterally enlarged adrenal glands. Which additional diagnostic finding would most strongly support a diagnosis of pituitary-dependent hyperadrenocorticism over adrenal-dependent disease?

Suppression of cortisol below 50% of baseline on high-dose dexamethasone suppression test (Correct answer)
Urine cortisol:creatinine ratio greater than 35 × 10⁻⁶
An ACTH stimulation post-cortisol value exceeding 30 µg/dL
Failure to suppress cortisol below 50% of baseline on high-dose dexamethasone suppression test

Correct answer: Suppression of cortisol below 50% of baseline on high-dose dexamethasone suppression test

In pituitary-dependent hyperadrenocorticism (PDH), the pituitary corticotroph tumor retains some negative feedback sensitivity to glucocorticoids. A high-dose dexamethasone suppression test (0.1 mg/kg IV) suppresses cortisol below 50% of baseline in approximately 75–80% of PDH cases, because the pituitary adenoma can still be partially inhibited. Adrenal-dependent tumors are autonomous and will NOT suppress regardless of dexamethasone dose. Bilateral adrenomegaly alone is consistent with PDH (bilateral cortical hyperplasia) but can occasionally be seen with bilateral adrenal tumors. The ACTH stimulation result confirms HAC but does not differentiate origin. UCCR is a sensitive screening tool but lacks specificity for differentiating PDH from ADH.

Question 182: A 72-year-old woman with chronic kidney disease (GFR 18 mL/min) is prescribed metformin by an urgent care provider. Three days later she presents obtunded with an arterial pH of 7.08, lactate of 14 mmol/L, and normal glucose. What is the pathophysiologic mechanism of her toxicity?

Metformin competitively inhibits gluconeogenesis from pyruvate, causing pyruvate to accumulate and convert to lactate
Accumulated metformin inhibits mitochondrial complex I, impairing oxidative phosphorylation and forcing anaerobic lactate production (Correct answer)
Metformin undergoes renal bioactivation to a toxic quinone metabolite that alkylates hepatocyte mitochondria
Metformin activates AMPK in renal tubular cells, suppressing ATP synthesis and causing systemic lactic acidosis

Correct answer: Accumulated metformin inhibits mitochondrial complex I, impairing oxidative phosphorylation and forcing anaerobic lactate production

Metformin-associated lactic acidosis (MALA) occurs primarily through inhibition of mitochondrial complex I (NADH dehydrogenase) of the electron transport chain. This impairs oxidative phosphorylation, forces cells into anaerobic glycolysis, and generates excess lactate. In renal impairment, metformin accumulates to toxic concentrations because it is cleared almost entirely by glomerular filtration. Metformin does inhibit hepatic gluconeogenesis (its therapeutic mechanism), but MALA's root cause is mitochondrial respiratory chain dysfunction.

Question 183: A 4-year-old Holstein dairy cow presents with a 3-day history of anorexia, decreased milk production, and progressive weakness. Blood work reveals: PCV 12%, total protein 5.2 g/dL, marked macrocytosis, hypersegmented neutrophils, and low serum cobalamin. Which condition BEST explains this presentation?

Iron deficiency from chronic subclinical hemorrhage
Cobalt deficiency leading to vitamin B12-responsive anemia (Correct answer)
Bovine leukemia virus-associated lymphoma
Copper deficiency causing secondary anemia

Correct answer: Cobalt deficiency leading to vitamin B12-responsive anemia

Ruminants cannot synthesize vitamin B12 (cobalamin) directly; they depend on ruminal microbes synthesizing it from dietary cobalt. Cobalt deficiency leads to B12 deficiency, which impairs methylmalonyl-CoA mutase and methionine synthase, producing a megaloblastic (macrocytic) anemia with hypersegmented neutrophils — identical to B12 deficiency in other species. The low serum cobalamin confirms the diagnosis. Copper deficiency causes a normocytic or microcytic anemia without hypersegmented neutrophils. BLV lymphoma does not typically cause megaloblastic changes. Iron deficiency produces microcytic, hypochromic anemia.

Question 184: A 7-year-old Doberman Pinscher with a history of von Willebrand disease (type I) is scheduled for elective gastropexy. Preoperative vWF antigen level is 18% (reference >60%). Which perioperative hemostatic management strategy is MOST appropriate prior to making the incision?

Administer desmopressin (DDAVP) 1 µg/kg IV 30 minutes before incision to stimulate endogenous vWF release from endothelial storage granules (Correct answer)
Administer epsilon-aminocaproic acid (EACA) IV loading dose prior to surgery to inhibit fibrinolysis
Pretreat with cryoprecipitate 1 unit per 10 kg body weight given 4 hours before surgery to allow equilibration
Transfuse fresh frozen plasma (FFP) at 10 mL/kg immediately before incision to replace vWF directly

Correct answer: Administer desmopressin (DDAVP) 1 µg/kg IV 30 minutes before incision to stimulate endogenous vWF release from endothelial storage granules

In type I von Willebrand disease, endothelial cells retain functional Weibel-Palade bodies containing vWF. Desmopressin (DDAVP) stimulates V2 receptors on endothelial cells, triggering release of stored vWF multimers and acutely raising vWF levels — often 2–3× baseline — within 30–60 minutes. This is the preferred first-line approach for elective procedures in type I vWD. Cryoprecipitate is the most vWF-concentrated blood product and is indicated when DDAVP response is insufficient or for types II/III vWD; however, its administration 4 hours before is suboptimal (it should be given just before incision due to short vWF half-life). FFP contains vWF but at lower concentration and requires large volumes. EACA addresses fibrinolysis, not the primary platelet adhesion defect.

Question 185: A 4-year-old Quarter Horse presents with progressive ataxia, dysphagia, and muscle wasting over 6 months. Necropsy reveals multifocal, nonsuppurative encephalomyelitis with intraneuronal protozoal organisms. Immunohistochemistry confirms Sarcocystis neurona. Which of the following best explains why cell-mediated immunity is the primary defense against this organism rather than humoral immunity?

Equine IgG subclasses cannot opsonize apicomplexan parasites due to their glycan coat composition
S. neurona resides within neurons, which lack MHC class I expression, preventing CD8+ T-cell recognition
S. neurona suppresses B-cell activation by secreting IL-10 analogs that block germinal center formation
S. neurona is an obligate intracellular parasite that evades antibody neutralization by residing within host cell cytoplasm (Correct answer)

Correct answer: S. neurona is an obligate intracellular parasite that evades antibody neutralization by residing within host cell cytoplasm

As an obligate intracellular parasite, S. neurona completes its life cycle within host cell cytoplasm (primarily neurons and macrophages), where circulating antibodies cannot reach the organism directly. Cell-mediated immunity — particularly CD8+ cytotoxic T lymphocytes and activated macrophages — is critical for eliminating infected cells. While serum antibodies are detectable and used diagnostically (IFAT, SAG ELISA), they are insufficient for clearance of established intracellular infection.

Question 186: A 6-year-old quarter horse presents with acute onset of moderate colic. On rectal palpation, you feel a tightly distended loop of small intestine in the right dorsal quadrant. Which diagnosis is most consistent with these findings?

Duodenal ulceration
Right dorsal displacement of the large colon
Gastric dilation
Ileal impaction (Correct answer)

Correct answer: Ileal impaction

Ileal impaction presents with moderate to severe colic and a palpable, firm, distended loop of small intestine on rectal examination, typically in the right dorsal abdomen.

Question 187: A goat herd experiences multiple abortions in the last trimester. Placental lesions show thickened, leathery cotyledons with tan exudate. Zoonotic risk is high. Which pathogen is most likely?

Chlamydophila abortus (Enzootic abortion)
Listeria monocytogenes
Coxiella burnetii (Q fever) (Correct answer)
Toxoplasma gondii

Correct answer: Coxiella burnetii (Q fever)

Coxiella burnetii causes abortion with characteristic placentitis and poses significant zoonotic risk to farm workers, veterinarians, and pregnant women through inhalation of contaminated aerosols.

Question 188: A 4-year-old intact male dog presents with scrotal edema, fever, and reluctance to breed. Brucella canis is suspected. Which serological test has the highest sensitivity for initial screening but is known to produce false positives due to cross-reactivity with other gram-negative bacteria?

Blood culture on Farrell's medium
Tube agglutination test (TAT)
Agar gel immunodiffusion (AGID)
Rapid slide agglutination test (RSAT) (Correct answer)

Correct answer: Rapid slide agglutination test (RSAT)

The Rapid Slide Agglutination Test (RSAT) is highly sensitive and used for initial screening, but it cross-reacts with other gram-negative organisms such as Pseudomonas, Bordetella, and Moraxella, leading to false positives. AGID targeting the cytoplasmic protein antigen is more specific. TAT is also prone to cross-reactivity. Blood culture is the gold standard but slow and requires BSL-2 precautions.

Question 189: A patient with chronic kidney disease (GFR 18 mL/min) requires analgesia. They are prescribed tramadol. Which pharmacokinetic and pharmacodynamic concern makes this combination particularly dangerous?

CKD causes hypoalbuminemia that increases free tramadol levels, potentiating serotonin syndrome
Reduced renal prostaglandin synthesis in CKD enhances tramadol's COX-inhibiting effects, causing acute tubular necrosis
Tramadol undergoes extensive renal tubular secretion, leading to competitive inhibition of creatinine excretion and falsely elevated serum creatinine
Active O-desmethyltramadol (M1 metabolite, a μ-opioid agonist) and the parent compound accumulate due to impaired renal clearance, increasing seizure and opioid toxicity risk (Correct answer)

Correct answer: Active O-desmethyltramadol (M1 metabolite, a μ-opioid agonist) and the parent compound accumulate due to impaired renal clearance, increasing seizure and opioid toxicity risk

Tramadol is partially converted by CYP2D6 to O-desmethyltramadol (M1), which has ~200-fold higher μ-opioid receptor affinity than the parent drug. Both tramadol and M1 are renally excreted. In CKD (especially GFR <30), their half-lives are prolonged dramatically, leading to accumulation. This raises risk of two distinct toxicities: (1) opioid toxicity from M1 accumulation (respiratory depression, CNS depression), and (2) seizures, since tramadol itself lowers seizure threshold via GABA modulation and norepinephrine/serotonin reuptake inhibition. Tramadol is generally contraindicated or used with extreme caution at GFR <30.

Question 190: A 55-year-old woman has a breast biopsy showing cells with large nuclei, prominent nucleoli, and loss of normal glandular architecture invading the stroma. What is the most appropriate classification?

Phyllodes tumor
Lobular carcinoma in situ
Invasive ductal carcinoma (Correct answer)
Fibroadenoma

Correct answer: Invasive ductal carcinoma

Invasive ductal carcinoma is characterized by malignant epithelial cells with stromal invasion, large nuclei, and prominent nucleoli.

Question 191: What causes emphysema in the first place?

Alpha-1 antitrypsin deficiency (Correct answer)
Asthma
Chronic bronchitis
Silicosis

Correct answer: Alpha-1 antitrypsin deficiency

In addition to being primarily brought on by cigarette smoking, alpha-1 antitrypsin deficiency can also cause emphysema by promoting unopposed protease activity and damaging alveolar tissue.

Question 192: A patient undergoes a nuclear medicine bone scan and demonstrates a 'superscan' pattern. Which of the following conditions is LEAST likely to produce this finding?

Multiple myeloma with purely lytic lesions and no osteoblastic response (Correct answer)
Widespread osteoblastic metastases from prostate carcinoma
Renal osteodystrophy with secondary hyperparathyroidism
Diffuse Paget disease involving the axial skeleton

Correct answer: Multiple myeloma with purely lytic lesions and no osteoblastic response

A superscan on bone scintigraphy shows diffusely increased skeletal uptake with absent or markedly reduced renal and soft-tissue activity, creating an apparently 'normal' but abnormally intense image. It occurs when osteoblastic activity is globally elevated — as in widespread osteoblastic metastases (e.g., prostate cancer), metabolic bone disease (renal osteodystrophy, hyperparathyroidism), or diffuse Paget disease. Multiple myeloma classically produces purely lytic lesions that stimulate no osteoblastic response; consequently, bone scan is often falsely negative and a superscan pattern would not be expected.

Question 193: Which of the following best describes the pathogenesis of Type D enterotoxemia (pulpy kidney disease) in sheep caused by Clostridium perfringens?

Beta toxin causes necrotic enteritis exclusively in neonatal piglets
Epsilon toxin produced in the gut increases intestinal permeability and causes cerebral edema (Correct answer)
Alpha toxin produced systemically lyses red blood cells causing hemolytic anemia
Iota toxin disrupts actin cytoskeleton causing flaccid paralysis

Correct answer: Epsilon toxin produced in the gut increases intestinal permeability and causes cerebral edema

In Type D enterotoxemia, epsilon toxin (activated from epsilon prototoxin) increases vascular permeability, leading to cerebral edema and characteristic pulpy kidney lesions.

Question 194: Which of the following best describes the mechanism of action of nonsteroidal anti-inflammatory drugs (NSAIDs) used for perioperative analgesia in veterinary patients?

Block NMDA receptors to prevent central sensitization
Inhibit cyclooxygenase enzymes, reducing prostaglandin synthesis (Correct answer)
Block sodium channels in peripheral nerves
Bind opioid receptors in the CNS

Correct answer: Inhibit cyclooxygenase enzymes, reducing prostaglandin synthesis

NSAIDs inhibit COX-1 and/or COX-2 enzymes, thereby reducing prostaglandin production and decreasing peripheral and central sensitization to pain.

Question 195: On a chest X-ray, a 'silhouette sign' is created when two structures of similar density are adjacent. Which finding indicates right middle lobe consolidation?

Loss of the right heart border (Correct answer)
Loss of the aortic knob
Blunting of the right costophrenic angle
Loss of the left heart border

Correct answer: Loss of the right heart border

The right middle lobe is adjacent to the right heart border, so consolidation there obliterates that border on PA chest X-ray.

Question 196: In the context of pharmacodynamics, how does a non-competitive antagonist affect the agonist dose-response curve?

Increases both the Emax and the EC50.
Shifts the curve to the left, decreasing the EC50.
Reduces the maximal response (Emax) without changing the EC50. (Correct answer)
Shifts the curve to the right, increasing the EC50.

Correct answer: Reduces the maximal response (Emax) without changing the EC50.

A non-competitive antagonist binds to a site on the receptor other than the agonist binding site (an allosteric site) or binds irreversibly to the active site. This action reduces the total number of receptors available to the agonist, thereby decreasing the maximal possible effect (Emax) that can be achieved, regardless of the agonist concentration. Because the antagonist does not compete for the same binding site, it does not change the agonist concentration required to achieve 50% of the *new* maximal response, so the EC50 is unchanged.

Question 197: A cat presents with acute vomiting, icterus, and marked elevation in serum lipase. Abdominal ultrasound reveals a hypoechoic pancreas with surrounding hyperechoic mesentery. Which supportive therapy is most important initially?

Oral pancreatic enzyme supplementation
Immediate surgical debridement
Aggressive IV fluid resuscitation and analgesia (Correct answer)
Corticosteroid administration

Correct answer: Aggressive IV fluid resuscitation and analgesia

Aggressive IV fluid therapy corrects hypovolemia and improves pancreatic microcirculation, and analgesia is essential in feline pancreatitis management.

Question 198: Which of the following is the most common cause of esophageal obstruction (choke) in horses?

Esophageal neoplasia
Poorly soaked sugar beet pulp or hay cubes (Correct answer)
Esophageal stricture from prior trauma
Foreign body ingestion

Correct answer: Poorly soaked sugar beet pulp or hay cubes

Improperly soaked beet pulp or hay cubes that expand with saliva and water in the esophagus are the most common cause of choke in horses.

Question 199: Which tumor suppressor gene, when mutated, causes familial adenomatous polyposis (FAP) and dramatically increases colorectal cancer risk?

BRCA1
RB1
APC (Correct answer)
TP53

Correct answer: APC

APC (adenomatous polyposis coli) gene mutations cause FAP; APC normally targets β-catenin for degradation, and its loss leads to uncontrolled Wnt signaling and polyp formation.

Question 200: On CT pulmonary angiography (CTPA), which finding is most specific for pulmonary embolism?

Pleural effusion
Atelectasis
A filling defect within an opacified pulmonary artery (Correct answer)
Consolidation in the lung periphery

Correct answer: A filling defect within an opacified pulmonary artery

A filling defect within a contrast-opacified pulmonary artery on CTPA is the direct and most specific sign of pulmonary embolism.

Question 201: Which feline reproductive characteristic distinguishes cats from dogs in terms of ovulation?

Cats ovulate only once per year
Cats require mating or cervical stimulation to ovulate (induced ovulation) (Correct answer)
Cats are spontaneous ovulators
Cats have a 21-day estrous cycle like cattle

Correct answer: Cats require mating or cervical stimulation to ovulate (induced ovulation)

Cats are induced ovulators, requiring coital or mechanical cervical stimulation to trigger the LH surge and subsequent ovulation.

Question 202: A lymph node biopsy from a 34-year-old HIV-positive man shows paracortical expansion by large cells with prominent nucleoli, abundant pale cytoplasm, and interspersed small lymphocytes. EBER in-situ hybridization is positive. CD30 is positive; CD15 is negative; CD20 is dim positive; PAX5 is weakly positive; CD45 is positive. What is the most likely diagnosis?

Plasmablastic lymphoma
Classic Hodgkin lymphoma, mixed cellularity subtype
EBV-positive diffuse large B-cell lymphoma, NOS (Correct answer)
EBV-positive polymorphic B-cell lymphoproliferative disorder

Correct answer: EBV-positive diffuse large B-cell lymphoma, NOS

EBV-positive DLBCL, NOS (formerly EBV-positive DLBCL of the elderly, now recognized across age groups especially in immunocompromised patients) characteristically shows CD20 dim positivity, PAX5 weak positivity, CD45 positivity, and CD30 positivity with EBER+. CD15 negativity and retained B-cell markers distinguish it from classic Hodgkin lymphoma. Plasmablastic lymphoma typically loses CD20/PAX5 entirely and is EBER+ but shows plasmacytic differentiation markers.

Question 203: During an outbreak investigation of Legionnaires' disease at a hotel, the attack rate among guests who used the rooftop pool was 18%, while among guests who did not use the pool it was 4%. The relative risk is 4.5 and the chi-square p-value is 0.003. The investigators then stratify by floor of residence and find that both the pool-users and non-pool-users on floors 8–10 (nearest the cooling tower) have similarly elevated attack rates. What does this stratified analysis most strongly suggest?

Floor of residence is a confounder that negates the pool association
The outbreak has multiple simultaneous point sources including both the pool and the tower
There is effect modification between pool use and floor of residence
The cooling tower, not the pool, is the likely primary source of the outbreak (Correct answer)

Correct answer: The cooling tower, not the pool, is the likely primary source of the outbreak

When stratification by floor shows that proximity to the cooling tower — not pool use — is the common factor driving elevated attack rates in both exposed and unexposed groups, it suggests the pool association was confounded by proximity to the cooling tower. Legionella typically colonizes cooling towers and aerosolizes through the ventilation system, reaching nearby floors regardless of pool use. The stratified analysis points to the cooling tower as the primary reservoir, a critical reorientation of the investigation.

Question 204: What is the term for the failure of one or both testes to descend into the scrotum in male dogs?

Ectopic testis
Cryptorchidism (Correct answer)
Anorchism
Orchitis

Correct answer: Cryptorchidism

Cryptorchidism describes the condition in which one (unilateral) or both (bilateral) testes fail to descend into the scrotal sac, predisposing to Sertoli cell tumors.

Question 205: During an outbreak investigation, a cohort study of foodborne illness at a catered event reveals the following: attack rate among those who ate the shrimp = 72%, attack rate among those who did NOT eat the shrimp = 68%. The relative risk is 1.06. What is the MOST appropriate conclusion?

Confounding by another food consumed simultaneously negates the relative risk calculation
Shrimp is confirmed as the causative vehicle given the high absolute attack rates
Shrimp is unlikely to be the causative vehicle; another food item should be investigated (Correct answer)
The study is underpowered and a larger cohort is needed before conclusions can be drawn

Correct answer: Shrimp is unlikely to be the causative vehicle; another food item should be investigated

A relative risk of 1.06 is very close to 1.0, indicating essentially no increased risk from eating shrimp. Despite the high absolute attack rates (suggesting a widespread exposure), the nearly identical rates in both groups means shrimp is not the differentiating factor. Classic outbreak investigation methodology requires identifying a food with a substantially elevated relative risk (typically >2.0) to implicate it as the vehicle. Another food item consumed by nearly everyone — regardless of shrimp consumption — is the more likely culprit.

Question 206: A patient presents with bradycardia, miosis, salivation, and urinary incontinence after exposure to an organophosphate pesticide. Which receptor is being overstimulated?

Nicotinic acetylcholine receptor
Muscarinic acetylcholine receptor (Correct answer)
Alpha-1 adrenergic receptor
Beta-2 adrenergic receptor

Correct answer: Muscarinic acetylcholine receptor

Organophosphates inhibit acetylcholinesterase, leading to accumulation of acetylcholine and overstimulation of muscarinic receptors, producing the classic SLUDGE syndrome.

Question 207: A patient with myasthenia gravis (MG) is scheduled for thymectomy. The anesthesiologist plans to avoid neuromuscular blocking agents. If a short-acting NMB is deemed necessary for intubation, which agent and reversal strategy represents the highest-risk approach in this patient?

Rocuronium 0.6 mg/kg reversed with sugammadex 16 mg/kg
Cisatracurium 0.1 mg/kg reversed with neostigmine 0.07 mg/kg and glycopyrrolate (Correct answer)
Mivacurium 0.15 mg/kg relying on plasma cholinesterase hydrolysis for offset
Succinylcholine 1.5 mg/kg with no reversal required

Correct answer: Cisatracurium 0.1 mg/kg reversed with neostigmine 0.07 mg/kg and glycopyrrolate

In myasthenia gravis, patients have dramatically reduced functional acetylcholine receptors, making them exquisitely sensitive to non-depolarizing NMBs — cisatracurium at 0.1 mg/kg (a normal intubating dose) can produce profound, prolonged blockade. Neostigmine reversal is particularly problematic because MG patients are already on cholinesterase inhibitors (e.g., pyridostigmine), and administering neostigmine risks cholinergic crisis in addition to unpredictable reversal. Rocuronium reversed with sugammadex is actually preferred in MG because sugammadex provides predictable, complete reversal independent of receptor status. Succinylcholine is controversial (risk of phase II block) but not requiring reversal. Mivacurium relies on plasma cholinesterase and, if normal enzyme levels, offsets quickly without reversal.

Question 208: During intestinal anastomosis, a surgeon performs a leak test. Which method is most commonly used intraoperatively to check for anastomotic leakage?

Apply fluorescein dye under UV light
Occlude the bowel on both sides of the anastomosis and gently milk intraluminal air toward the site while submerging in saline (Correct answer)
Request intraoperative endoscopy
Inject methylene blue through a nasogastric tube

Correct answer: Occlude the bowel on both sides of the anastomosis and gently milk intraluminal air toward the site while submerging in saline

The air-leak test involves occluding the bowel on each side, injecting air or milking intraluminal gas toward the anastomosis submerged in saline, and watching for bubbles indicating a leak.

Question 209: A 10-year-old spayed female Doberman Pinscher with dilated cardiomyopathy and recent syncope is being treated with pimobendan, furosemide, and enalapril. An 18-lead Holter monitor reveals 4,800 ventricular premature complexes over 24 hours, including several R-on-T events. The owner reports the dog ate a large meal of canned salmon the previous evening. Which intervention is most appropriate at this point?

Switch pimobendan to digoxin for better rate control and add mexiletine, since pimobendan is contraindicated once VPCs exceed 3,000 per 24 hours on Holter monitoring.
Add mexiletine at 5–8 mg/kg PO TID as the primary antiarrhythmic of choice for Doberman DCM-associated ventricular arrhythmias, and recheck Holter in 4–6 weeks. (Correct answer)
Add sotalol at 1–2 mg/kg PO BID, recheck Holter in 4–6 weeks to assess antiarrhythmic efficacy, and measure serum taurine and carnitine levels before making dietary changes.
Immediately discontinue furosemide because loop diuretic-induced hypomagnesemia is the primary cause of R-on-T complexes in Dobermans, and replace it with spironolactone.

Correct answer: Add mexiletine at 5–8 mg/kg PO TID as the primary antiarrhythmic of choice for Doberman DCM-associated ventricular arrhythmias, and recheck Holter in 4–6 weeks.

Mexiletine is the preferred first-line antiarrhythmic for ventricular arrhythmias in Doberman Pinschers with DCM; it is a Class IB sodium channel blocker well-tolerated in myopathic dogs. Sotalol is a reasonable second choice but carries more negative inotropy risk in decompensated DCM. Pimobendan remains indicated and is not contraindicated by VPC count thresholds. Furosemide-induced hypomagnesemia can contribute but is not the sole driver, and discontinuing it in a volume-overloaded patient would be dangerous. Taurine/carnitine testing is valuable but does not change the immediate antiarrhythmic decision.

Question 210: Which toxic effect is associated with methanol poisoning but not ethanol poisoning?

Central nervous system depression and respiratory failure
Wernicke encephalopathy due to thiamine depletion
Severe metabolic acidosis with visual disturbances and blindness (Correct answer)
Hypoglycemia due to NAD+ depletion

Correct answer: Severe metabolic acidosis with visual disturbances and blindness

Methanol is metabolized to formaldehyde and formic acid by alcohol dehydrogenase; formate accumulates in the retina and optic nerve, causing irreversible blindness and severe anion-gap metabolic acidosis.

Question 211: A surgeon is performing a total ear canal ablation and lateral bulla osteotomy (TECA-LBO) in a dog with end-stage otitis. Postoperatively, the patient shows an ipsilateral facial nerve paralysis and Horner syndrome. Which of the following statements most accurately characterizes the expected prognosis and underlying anatomical explanation?

Horner syndrome resolves if caused by middle ear inflammation rather than nerve transection; facial nerve deficits resolve in 6–8 weeks if neuropraxia rather than axonotmesis (Correct answer)
Facial nerve paralysis is typically permanent; Horner syndrome often resolves within 4–8 weeks as postganglionic fibers regenerate via alternative pathways
Permanent Horner syndrome is expected because the sympathetic trunk is transected during bulla curettage; facial nerve paralysis typically resolves within 3–6 weeks
Both deficits are expected to be permanent because the facial nerve and postganglionic sympathetic fibers both course through the petrous temporal bone and are invariably severed

Correct answer: Horner syndrome resolves if caused by middle ear inflammation rather than nerve transection; facial nerve deficits resolve in 6–8 weeks if neuropraxia rather than axonotmesis

Both deficits can be neuropraxic (traction or thermal injury) or result from more severe axonotmesis/neurotmesis. If Horner syndrome arises from perioperative middle ear inflammation compressing the postganglionic sympathetic fibers (which traverse the tympanic bulla), it is more likely to resolve as inflammation subsides. Facial nerve paralysis prognosis depends on severity—neuropraxia recovers in weeks, while axonotmesis may take months or may not fully recover. Neither deficit is invariably permanent. This nuanced prognosis distinguishes it from the other options that overstate permanence or simplify recovery timelines.

Question 212: A 3-week-old foal presents with bilateral uveitis, polyarthritis, hypopyon, and a serum IgG of 200 mg/dL. Blood culture is pending. Which pathogen, if isolated, would MOST strongly support a diagnosis of Rhodococcus equi?

A gram-negative, encapsulated rod that produces a heat-stable enterotoxin
A gram-positive, weakly acid-fast, pleomorphic coccobacillus that is catalase and urease positive (Correct answer)
A gram-positive coccus arranged in chains that is beta-hemolytic on blood agar
A motile, gram-negative rod that ferments lactose and is oxidase negative

Correct answer: A gram-positive, weakly acid-fast, pleomorphic coccobacillus that is catalase and urease positive

Rhodococcus equi is a gram-positive, pleomorphic coccobacillus that is weakly acid-fast (Ziehl-Neelsen positive), catalase positive, and urease positive. It is the classic cause of suppurative pneumonia in foals 1–6 months old and can cause extrapulmonary lesions including uveitis, polyarthritis, and hypopyon, particularly in immunocompromised foals (failure of passive transfer with IgG of 200 mg/dL is severe FPT). The other choices describe organisms inconsistent with R. equi: gram-negative encapsulated rods suggest Klebsiella or Mannheimia; beta-hemolytic gram-positive chains suggest Streptococcus; lactose-fermenting gram-negative motile rods suggest Enterobacteriaceae such as E. coli.

Question 213: Which immunoglobulin class is the predominant antibody in colostrum and provides passive mucosal immunity to the neonatal gastrointestinal tract?

IgM
IgG
IgA (Correct answer)
IgE

Correct answer: IgA

Secretory IgA (sIgA) is the dominant immunoglobulin in colostrum and mucosal secretions. It is transported across epithelial cells via the polymeric immunoglobulin receptor (pIgR) and resists proteolytic digestion in the gut lumen, making it critical for neonatal mucosal defense. IgG predominates in serum; IgM is the first antibody produced in primary responses; IgE is involved in allergic reactions.

Question 214: Borna disease virus causes encephalitis primarily in horses in central Europe. To which order does this neurotropic negative-sense RNA virus belong?

Mononegavirales (Correct answer)
Nidovirales
Picornavirales
Herpesvirales

Correct answer: Mononegavirales

Borna disease virus belongs to the family Bornaviridae within the order Mononegavirales, which includes other non-segmented negative-sense RNA viruses like rhabdoviruses and paramyxoviruses.

Question 215: Which bacterial pathogen is the most common cause of leptospirosis in dogs in the United States?

Ehrlichia canis
Leptospira interrogans serovars Canicola and Icterohaemorrhagiae (Correct answer)
Borrelia burgdorferi
Brucella canis

Correct answer: Leptospira interrogans serovars Canicola and Icterohaemorrhagiae

Leptospira interrogans serovars Canicola and Icterohaemorrhagiae are the serovars most frequently associated with leptospirosis in US dogs.

Question 216: A 10-year-old West Highland White Terrier is presented for a chronic, non-productive cough. Thoracic radiographs reveal prominent, thickened bronchial walls, which appear as 'doughnuts' on end-on views and 'tramlines' when viewed longitudinally. The lung fields appear mildly hyperinflated, but there is no evidence of an alveolar pattern or cardiomegaly. Which of the following is the most likely diagnosis?

Aspiration pneumonia
Pulmonary neoplasia
Cardiogenic pulmonary edema
Chronic bronchitis (Correct answer)

Correct answer: Chronic bronchitis

The radiographic signs described, including thickened bronchial walls seen as 'doughnuts' and 'tramlines', are classic for a bronchial lung pattern. In an older small breed dog with a chronic cough, this pattern is most consistent with chronic bronchitis. Aspiration pneumonia typically presents with an alveolar pattern in the cranioventral lung fields. Cardiogenic edema usually involves an interstitial to alveolar pattern, often in the perihilar or caudodorsal regions, along with cardiomegaly. Pulmonary neoplasia would more likely present as a distinct mass or a structured interstitial (nodular) pattern.

Question 217: A 6-year-old Thoroughbred mare presents with acute onset of severe colic, marked abdominal distension, and spontaneous cecal tympany on rectal palpation. Despite initial treatment, the cecum remains markedly distended. Which of the following is the MOST appropriate next step if medical management fails after 12–24 hours?

Oral administration of mineral oil via nasogastric tube
Exploratory laparotomy with typhlotomy or cecopexy (Correct answer)
Trocarization of the cecum via right paralumbar fossa
Administration of IV neostigmine at 0.022 mg/kg

Correct answer: Exploratory laparotomy with typhlotomy or cecopexy

Cecal impaction and tympany refractory to medical management carries a high risk of cecal rupture and requires surgical intervention. Exploratory laparotomy allows for typhlotomy (evacuation), cecopexy to prevent recurrence, or partial typhlectomy if the cecum is compromised. Trocarization can provide temporary relief but does not address the underlying cause and carries contamination risk. Neostigmine can worsen spasmodic pain and is not indicated for cecal tympany refractory to initial treatment. Mineral oil via nasogastric tube has no meaningful effect on cecal outflow obstruction.

Question 218: A 58-year-old patient with alcoholic cirrhosis is started on a high-protein diet to address sarcopenia. Which metabolic derangement MOST limits the use of standard branched-chain amino acid catabolism in this patient's skeletal muscle?

Impaired hepatic urea cycle reducing total ammonia clearance
Insulin resistance abolishing leucine-mediated mTORC1 activation
Decreased activity of branched-chain α-keto acid dehydrogenase complex in muscle (Correct answer)
Elevated plasma aromatic amino acids competitively inhibiting BCAA transport

Correct answer: Decreased activity of branched-chain α-keto acid dehydrogenase complex in muscle

In cirrhosis, skeletal muscle becomes a primary site of ammonia detoxification via glutamine synthesis, consuming α-ketoglutarate. The resulting depletion of TCA cycle intermediates downregulates branched-chain α-keto acid dehydrogenase (BCKDH) complex activity, impairing complete oxidation of BCAAs in muscle. This creates a metabolic block specifically in BCAA catabolism at the mitochondrial level, which is distinct from — though compounded by — impaired hepatic urea synthesis.

Question 219: Epidural anesthesia is established at L3-L4. Which abdominal surgery would NOT be adequately covered by this block alone?

Appendectomy
Inguinal hernia repair
Cesarean section
Cholecystectomy (Correct answer)

Correct answer: Cholecystectomy

Cholecystectomy requires anesthesia to T4 level, and diaphragmatic irritation (phrenic nerve C3-C5) cannot be blocked by lumbar epidural, making general anesthesia necessary.

Question 220: A 4-year-old thoroughbred racehorse presents with exercise intolerance and a grade 4/6 holosystolic murmur loudest at the left cardiac apex. What is the most likely diagnosis?

Tricuspid regurgitation
Mitral regurgitation (Correct answer)
Ventricular septal defect
Aortic regurgitation

Correct answer: Mitral regurgitation

Mitral regurgitation produces a holosystolic murmur heard loudest at the left cardiac apex (mitral valve area) in horses.

Question 221: Which measure best describes the probability that a person with a positive screening test truly has the disease?

Positive predictive value (Correct answer)
Sensitivity
Specificity
Negative predictive value

Correct answer: Positive predictive value

Positive predictive value (PPV) is the proportion of true positives among all positive test results.

Question 222: A dog undergoing orthopedic surgery develops shivering and a rectal temperature of 35.5°C (95.9°F). Which intraoperative measure is MOST effective in preventing further heat loss?

Use forced-air warming blankets and warm IV fluids (Correct answer)
Place ice packs around the neck
Administer IV dexamethasone
Increase the anesthetic gas concentration

Correct answer: Use forced-air warming blankets and warm IV fluids

Forced-air warming blankets are the most effective active rewarming modality during surgery, and warming IV fluids prevents further core temperature loss.

Question 223: During AI in a dairy herd, a bull's frozen semen shows 65% post-thaw progressive motility and normal morphology, yet conception rates remain below 40% after multiple inseminations. Sperm chromatin structure assay (SCSA) reveals a DNA fragmentation index (DFI) of 28%. Which statement best explains this discrepancy and the clinical implication?

DNA fragmentation at this level only affects male offspring viability and has no effect on overall conception rates
A DFI >25% indicates high sperm DNA damage that impairs embryo development past the maternal-to-embryonic genome transition, despite normal motility (Correct answer)
The DFI of 28% is within normal limits; the low conception rates are attributable to inseminator technique rather than semen quality
High DFI causes failure of sperm capacitation in the oviduct, preventing zona penetration and fertilization

Correct answer: A DFI >25% indicates high sperm DNA damage that impairs embryo development past the maternal-to-embryonic genome transition, despite normal motility

A DFI >25% on SCSA is associated with significantly reduced fertility in cattle despite normal conventional semen parameters. DNA-damaged sperm can fertilize oocytes but embryos fail at or around the maternal-to-embryonic genome activation (MET) — occurring at the 8–16 cell stage in cattle — resulting in early embryonic death. This explains normal motility with poor field fertility. DFI does not impair capacitation or zona penetration directly.

Question 224: Which feeding strategy best supports the behavioral welfare of dogs in kennel environments?

One large meal daily delivered in a bowl
Caloric restriction to prevent boredom eating
Free-choice dry kibble available 24 hours
Food puzzles and scatter feeding that extend foraging time (Correct answer)

Correct answer: Food puzzles and scatter feeding that extend foraging time

Cognitive and physical engagement during feeding through puzzles or scatter feeding mimics natural foraging, reduces boredom, and decreases stress-related behaviors.

Question 225: The avian renal portal system is physiologically unique among domestic species. Which of the following correctly describes how this system can confound drug pharmacokinetics in birds?

Drugs injected into the caudal half of the body may be delivered directly to the renal tubular cells and undergo renal extraction or secretion before reaching systemic circulation, reducing bioavailability (Correct answer)
Drugs injected into the caudal half of the body may undergo first-pass hepatic metabolism before reaching systemic circulation because portal blood drains directly into the liver before the caudal vena cava
Drugs injected cranial to the synsacrum are subject to renal portal filtration because the renal portal vein receives blood from the jugular anastomosis
The avian renal portal system shunts blood away from the kidneys during digestion, so post-prandial drug injections in the caudal body have enhanced systemic bioavailability

Correct answer: Drugs injected into the caudal half of the body may be delivered directly to the renal tubular cells and undergo renal extraction or secretion before reaching systemic circulation, reducing bioavailability

In birds, the renal portal system carries blood from the caudal limbs and tail through the afferent renal portal veins directly to the peritubular capillaries of the kidney — before that blood returns to the heart via the caudal renal veins and caudal vena cava. Drugs (especially those with significant renal tubular secretion, e.g., penicillins, aminoglycosides) injected into the pectoral muscles or anywhere cranial to the synsacrum bypass this system. Injections into the leg or caudal body may be subject to renal extraction, effectively lowering systemic drug levels. The first-pass effect described in option A is hepatic, not what the renal portal system does.

Basic and Clinical Sciences Examination (BCSE)

The BCSE is administered by the AVMA ECFVG program to assess veterinary graduates' knowledge of basic and clinical sciences at the level expected of an entry-level US veterinarian. It consists of 225 multiple-choice questions completed in 220 minutes.

225

Questions

220 min

Time Limit

70%

To Pass

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