Question

Time of ovulation in cow is:

• A. 30-36 hours from beginning of estrus
• B. 30-45 hours from beginning of estrus
• C. 10-11 hours after end of estrus
• D. 1-2 days before end of estrus

Hint:

Cows are famous in theriogenology exams for being "metestrous ovulators" (ovulating *after* standing heat has ended).
This physiological quirk is the scientific basis for the AM-PM rule of artificial insemination.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Unlike most domestic species that ovulate during estrus (standing heat), the cow is unique because she ovulates during metestrus, after standing estrus has completely ended.

Step 2: Detailed Explanation:
Let us look at the temporal timeline of the bovine estrous cycle:
- The duration of standing estrus in a cow is short, typically lasting about 12 to 18 hours.
- Ovulation is triggered by the luteinizing hormone (LH) surge, which occurs at the onset of estrus.
- In cows, ovulation takes place approximately 30 hours after the LH surge, which corresponds to 10 to 11 hours after the end of estrus (standing heat).
- Because of this delay, artificial insemination (AI) is timed based on the "AM-PM rule" (cows observed in heat in the morning are inseminated in the evening, and vice versa) to ensure viable sperm are present in the oviduct when ovulation occurs.

Step 3: Final Answer:
Therefore, the correct time of ovulation in cows is 10-11 hours after the end of estrus.