Theriogenology and Veterinary Reproduction Flashcards

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?

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.

A 14-year-old Thoroughbred mare at approximately 145 days of gestation presents with vulvar discharge and premature mammary development. Transrectal ultrasonography reveals a combined thickness of uterus and placenta (CTUP) of 12 mm at the cervical star (normal <8 mm at this gestational age), with focal placental separation and grossly visible grayish-white mucoid plaques on the allantochorion surface. Which organism is MOST specifically associated with this ultrasonographic and gross pathological pattern?

Answer: Nocardioform actinomycetes (e.g., Crossiella equi, Amycolatopsis spp.)

Nocardioform actinomycetes produce a pathognomonic ascending placentitis pattern characterized by mucoid, brownish-gray plaques specifically at the cervical star region of the allantochorion — the finding described here. This gross lesion pattern definitively distinguishes nocardioform infection from other etiologies. Streptococcus zooepidemicus is the most frequently isolated organism in equine placentitis overall but does not produce the characteristic mucoid plaque lesion. EHV-4 causes hematogenous placentitis affecting the body and horns of the uterus, not ascending cervical star involvement. Leptospira causes late-gestation abortion via a different mechanism without this gross lesion.

A queen was bred to a tom cat 40 days ago and never returned to estrus. She is presented for a slightly enlarged abdomen. Radiography and ultrasonography reveal no fetuses, no uterine fluid accumulation, and no mass lesions. Serum progesterone is 12 ng/mL. Which statement MOST accurately explains the elevated progesterone in the absence of pregnancy or pyometra?

Answer: Cats can form functional corpora lutea following a coital LH surge even without oocyte release or fertilization, sustaining pseudopregnancy for 35–45 days

Cats are induced ovulators requiring a coital neurological stimulus to trigger an LH surge. However, that LH surge can cause luteinization of follicles even without successful ovulation (luteinized unruptured follicles), or ovulation can occur without fertilization — both resulting in functional CL formation and pseudopregnancy lasting approximately 35–45 days with progesterone in the 5–20 ng/mL range. Queens in true anestrus/interestrus have progesterone <1 ng/mL, ruling out option C. Adrenal progesterone is physiologically negligible in cats, ruling out option B.

A bull breeding soundness evaluation in a 30-month-old beef bull reveals 28% of sperm with a corkscrew midpiece (dag defect). The bull was recently housed in a poorly ventilated barn during a summer heat wave. Which statement regarding the dag defect is MOST accurate?

Answer: The defect represents aberrant mitochondrial sheath assembly during spermatogenesis and may resolve after approximately one full spermatogenic cycle if the inciting insult is removed

The dag defect (named after Danish researcher Dag) involves aberrant coiling or folding of the mitochondrial sheath in the sperm midpiece, arising from errors during spermiogenesis in the testis. When caused by environmental insults — particularly heat stress, zinc deficiency, or nutritional imbalance — the defect is potentially REVERSIBLE. Because the bovine spermatogenic cycle is approximately 61 days, it takes roughly two months after the inciting insult is removed for the ejaculate to reflect recovered spermatogenesis. High percentages (>25%) significantly impair fertilizing capacity and fail BSE criteria. A hereditary form exists in some breeds but is not strictly Y-linked and does not account for all cases.

Serial progesterone values in a bitch are: Day 0 = 1.2 ng/mL, Day 2 = 4.9 ng/mL, Day 4 = 9.6 ng/mL. Vaginal cytology on Day 4 shows 95% superficial cells. Frozen-thawed semen intrauterine insemination is planned. What is the OPTIMAL timing for insemination?

Answer: Day 6 — approximately 4 days post-estimated LH surge, allowing oocyte maturation to metaphase II before insemination with short-lived frozen-thawed semen

The LH surge in dogs corresponds to the initial progesterone rise above ~1.5–2.0 ng/mL — estimated here around Day 1–2. Ovulation follows the LH surge by approximately 48 hours (~Day 3–4). Critically, canine oocytes are ovulated in primary oocyte stage (meiosis I arrest) and require an additional 48–72 hours of oviductal maturation to reach metaphase II (fertilizable stage). The earliest fertilizable window is therefore approximately Day 5–6 (4 days post-LH). Frozen-thawed semen has a viable lifespan of only 12–24 hours post-thaw, requiring precise timing at peak oocyte fertility. Day 6 optimally coincides oocyte maturation with viable sperm.

On Day 7 post-estrus bovine embryo flush, you recover a compact morula with approximately 30–35% of the cellular mass appearing darker and vesiculated, but the gross overall spherical structure of the morula remains intact. According to the IETS (International Embryo Technology Society) grading scale, this embryo is best classified as which grade, and what is the approximate expected fresh-transfer pregnancy rate compared to a Grade 1 blastocyst?

Answer: Grade 3 (fair); pregnancy rates approximately 20–25 percentage points lower than Grade 1 (approximately 35–45% vs. 55–65%)

The IETS grading scale defines Grade 3 (fair) as embryos with 25–50% degenerated or morphologically abnormal cells in an otherwise intact overall structure — exactly matching the 30–35% vesiculated/dark cell mass described here. Grade 3 embryos are transferable but carry significantly reduced pregnancy rates: approximately 35–45% for fresh transfer versus 55–65% for Grade 1, a 20–25 percentage point reduction. Grade 4 embryos exceed 50% cellular degeneration or show non-viable characteristics and are discarded. The key distinction from Grade 2 (10–25% defects) is the percentage threshold — 30–35% clearly falls in the Grade 3 range.