DVM Reproductive Medicine and Theriogenology 2 — Questions and Answers
Question 1: Superovulation in cattle for embryo transfer is most commonly induced by:
- Exogenous FSH or eCG administered during the mid-luteal phase to stimulate multiple follicle development (Correct answer)
- Progesterone implants to increase the number of implantation sites
- GnRH administration on day 7 to recruit additional follicles
- Surgical removal of one ovary to concentrate follicular stimulation
Correct answer: Exogenous FSH or eCG administered during the mid-luteal phase to stimulate multiple follicle development
Multiple ovulations for embryo transfer are induced by exogenous FSH (given in decreasing doses over 4 days) or a single eCG injection during the mid-luteal phase, resulting in several transferable embryos.
Question 2: In swine, maternal recognition of pregnancy requires a minimum number of viable embryos because:
- Fewer than 4–5 embryos produce insufficient estrogen to rescue corpora lutea from prostaglandin-mediated regression (Correct answer)
- The uterus can only implant a limited number of conceptuses regardless of embryo number
- Sows require a viral signal from embryos rather than a hormonal one
- The corpus luteum in pigs is not luteotropic and requires mechanical distension
Correct answer: Fewer than 4–5 embryos produce insufficient estrogen to rescue corpora lutea from prostaglandin-mediated regression
Porcine embryos must produce sufficient estrogen by days 11–12 to redirect uterine PGF2α secretion away from the vasculature, rescuing the CL; fewer than approximately 4–5 embryos fails to provide adequate signal.
Question 3: Rectal palpation of pregnancy in mares typically becomes reliably diagnostic at approximately:
- Day 10–14
- Day 25–30 (Correct answer)
- Day 60–70
- Day 90–100
Correct answer: Day 25–30
Although ultrasound detects equine pregnancy from day 10–12, rectal palpation reliably identifies pregnancy at approximately day 25–30 when the uterine bulge and altered uterine tone are palpable.
Question 4: Prolonged diestrus (persistent corpus luteum) in mares is characterized by:
- Failure of the CL to regress beyond the normal luteal phase, with sustained progesterone suppressing estrus (Correct answer)
- Premature luteolysis leading to anovulatory estrus
- Corpus luteum formation without prior ovulation
- Abnormally short diestrus with frequent estrus cycles
Correct answer: Failure of the CL to regress beyond the normal luteal phase, with sustained progesterone suppressing estrus
Persistent CL in mares occurs when normal PGF2α-mediated luteolysis fails, often following early embryonic death, resulting in persistently elevated progesterone and behavioral anestrus.
Question 5: The standard cryoprotectant used in equine semen cryopreservation is:
- Dimethyl sulfoxide (DMSO)
- Glycerol (Correct answer)
- Ethylene glycol
- Propylene glycol
Correct answer: Glycerol
Glycerol (typically 2–5%) is the standard cryoprotectant for stallion semen freezing; it penetrates sperm membranes and protects against intracellular ice crystal formation during cryopreservation.
Question 6: In dogs, which serum progesterone concentration most closely corresponds to the preovulatory LH surge?
- Less than 0.5 ng/mL (basal level)
- 1–2 ng/mL (initial progesterone rise) (Correct answer)
- 5–10 ng/mL (post-ovulation)
- Greater than 20 ng/mL (mid-diestrus)
Correct answer: 1–2 ng/mL (initial progesterone rise)
The canine LH surge coincides with a progesterone rise to approximately 1–2 ng/mL; ovulation follows ~48 hours later at ~5 ng/mL, and fertilizable oocytes are present when progesterone reaches 10–25 ng/mL.
Question 7: The most common cause of early embryonic mortality in cattle is considered to be:
- Chromosomal abnormalities in the conceptus
- Failure of maternal recognition of pregnancy due to inadequate interferon-tau (IFN-τ) production (Correct answer)
- Luteal phase deficiency resulting in insufficient progesterone support
- Subclinical uterine infections present at the time of AI
Correct answer: Failure of maternal recognition of pregnancy due to inadequate interferon-tau (IFN-τ) production
Failure of maternal recognition of pregnancy, caused by insufficient IFN-τ from the trophoblast to prevent endometrial PGF2α secretion, is the leading cause of early embryonic loss in cattle.
DVM Reproductive Medicine and Theriogenology 2
Superovulation in cattle for embryo transfer is most commonly induced by: