Question

Inter- oestrous length of 30-35 days in bovine is an indication of

• A. Delayed ovulation
• B. $3^{\text{rd}}$ degree endometritis
• C. Early embryonic mortality
• D. Fertilization failure

Hint:

If a bred cow returns to heat at 21 days, it is a fertilization failure or embryonic death before maternal recognition. If she returns at 30-35 days, she was pregnant, but suffered early embryonic mortality.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The normal estrous cycle length in cattle is 21 days (with a normal range of 18-24 days).
Deviations from this interval are indicative of reproductive pathologies or alterations in the maternal recognition of pregnancy.

Step 2: Detailed Explanation:
Let us analyze the causes of altered inter-estrous intervals in cattle:
- If fertilization fails, or if ovulation is delayed, the uterine luteolytic mechanism (release of Prostaglandin \(F_{2\alpha}\)) will occur on schedule at day 16-17.
The corpus luteum regresses, and the cow returns to estrus within the normal 18-24 day interval.
- If fertilization is successful, the developing conceptus must signal its presence to the mother to prevent luteolysis, a process called maternal recognition of pregnancy (occurring around day 16-17).
- If early embryonic mortality occurs *after* the maternal recognition of pregnancy (i.e., after day 17), the corpus luteum is maintained for a prolonged period.
By the time the embryo dies and the luteolytic cascade is finally re-established, the luteal phase has been prolonged, delaying the return to estrus.
This results in an abnormally long, irregular inter-estrous interval of 30-35 days.

Step 3: Final Answer:
An inter-oestrous length of 30-35 days in bovine is a classic indication of early embryonic mortality.