Large Animal Internal Medicine Flashcards

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?

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.

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?

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.

A 10-year-old Quarter Horse gelding presents with a 6-month history of intermittent exertional myopathy, muscle fasciculations, and exercise intolerance. Muscle biopsy reveals abnormal polysaccharide accumulations within myofibers. Genetic testing confirms a GYS1 gene mutation. Which dietary modification is MOST evidence-based for long-term management?

Answer: High-fat, low-starch/sugar diet with regular, consistent exercise

This horse has Type 2 Polysaccharide Storage Myopathy (PSSM2) due to a GYS1 mutation causing constitutively active glycogen synthase and abnormal polysaccharide accumulation. Management centers on reducing dietary non-structural carbohydrates (starch and sugar) to minimize glycogen substrate while providing fat as an alternative energy source. Consistent, gradual exercise promotes proper glycogen metabolism. High-grain diets would worsen the condition by providing excess glucose substrate. Selenium supplementation alone does not address the underlying metabolic defect. Dantrolene is used for malignant hyperthermia prophylaxis, not PSSM.

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?

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.

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?

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.

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?

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.