DVM Reproductive Medicine and Theriogenology 1 — Questions and Answers
Question 1: In cattle, what is the average length of the estrous cycle?
- 14 days
- 21 days (Correct answer)
- 28 days
- 35 days
Correct answer: 21 days
The bovine estrous cycle averages 21 days (range 18–24 days), which is the standard interval used in synchronization and breeding management protocols.
Question 2: Which hormone is primarily responsible for luteolysis in most domestic species?
- Progesterone
- Luteinizing hormone (LH)
- Prostaglandin F2α (PGF2α) (Correct answer)
- Follicle-stimulating hormone (FSH)
Correct answer: Prostaglandin F2α (PGF2α)
Prostaglandin F2α (PGF2α), produced by the endometrium, causes regression of the corpus luteum in most domestic species and is used clinically to synchronize estrus.
Question 3: The 'freemartin' condition in cattle occurs when:
- A heifer born twin to a bull shares placental circulation, allowing masculinizing hormones to affect her reproductive tract (Correct answer)
- A cow develops an abnormally prolonged estrous cycle
- A heifer develops cystic ovarian disease after her first estrus
- A bull is exposed to estrogen-contaminated feed during puberty
Correct answer: A heifer born twin to a bull shares placental circulation, allowing masculinizing hormones to affect her reproductive tract
Freemartinism results from vascular anastomoses between bovine twins of different sexes, allowing Müllerian inhibiting substance and Y-bearing cells to masculinize the female twin's reproductive tract.
Question 4: In dogs, a primary reason bitches fail to conceive despite multiple breedings is:
- Breeding too early in proestrus before any LH rise
- Breeding at the wrong time relative to ovulation because canine oocytes require additional maturation time after ovulation (Correct answer)
- Exclusive male infertility with no female contribution
- Excessive progesterone production that prevents fertilization
Correct answer: Breeding at the wrong time relative to ovulation because canine oocytes require additional maturation time after ovulation
Canine oocytes are released immature at ovulation and require an additional 48–72 hours to become fertilizable; breeding must be timed precisely (typically 2–5 days post-LH surge) to achieve conception.
Question 5: After approximately day 150 of equine gestation, the primary source of progesterone maintaining pregnancy shifts to:
- The primary corpus luteum of pregnancy
- The fetoplacental unit (Correct answer)
- Accessory corpora lutea formed from eCG stimulation
- The adrenal cortex of the mare
Correct answer: The fetoplacental unit
After day 150, the primary CL and accessory CLs regress in mares, and the fetoplacental unit assumes responsibility for progesterone production to maintain pregnancy through term.
Question 6: Pyometra in dogs is most commonly associated with which phase of the reproductive cycle?
- Proestrus
- Estrus
- Diestrus (Correct answer)
- Anestrus
Correct answer: Diestrus
Pyometra typically develops during diestrus when sustained progesterone elevation stimulates endometrial proliferation and suppresses uterine immune defenses, predisposing to bacterial colonization.
Question 7: The Ovsynch protocol in cattle achieves synchronized, fixed-time artificial insemination by:
- GnRH injection to initiate a new follicular wave, followed by PGF2α to lyse the CL, then a second GnRH to induce ovulation (Correct answer)
- Progesterone implant for 7 days followed by estradiol benzoate to synchronize estrus
- Repeated FSH injections for superovulation followed by a single LH injection
- Melatonin administration to manipulate photoperiod and reset the cycle
Correct answer: GnRH injection to initiate a new follicular wave, followed by PGF2α to lyse the CL, then a second GnRH to induce ovulation
Ovsynch uses GnRH (day 0) to synchronize a follicular wave, PGF2α (day 7) to regress the CL, and a second GnRH (day 9) to induce synchronized ovulation ~16 hours later for timed AI.
DVM Reproductive Medicine and Theriogenology 1
In cattle, what is the average length of the estrous cycle?