Question

In cows, which phase of oestrus cycle is of shortest and of longest duration

• A. Oestrous and Dioestrus, respectively
• B. Oestrous and Metestrus, respectively
• C. Proestrus and Dioestrus, respectively
• D. Proestrus and Metestrus, respectively

Hint:

- Estrus (shortest): 12--18 hours, dominated by estrogen (standing heat).
- Diestrus (longest): 10--14 days, dominated by progesterone (fully functional CL).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The estrous cycle of a cow is a repetitive physiological cycle that averages 21 days in duration.
It is divided into four distinct phases: proestrus, estrus, metestrus, and diestrus, each dominated by specific hormones and ovarian structures.

Step 2: Detailed Explanation:
Let us analyze the duration of each phase in the bovine estrous cycle:
- Estrus (heat): This is the period of sexual receptivity when the cow stands to be mounted.
It is dominated by estrogen secreted by the mature Graafian follicle.
This phase has the shortest duration, lasting only 12 to 18 hours in cows.
- Metestrus: This is the post-ovulatory phase during which the ruptured follicle transitions into a developing corpus luteum.
It lasts for approximately 3 to 4 days.
- Diestrus: This is the luteal phase of the cycle, characterized by a fully functional, mature corpus luteum producing high levels of progesterone.
It is the longest phase of the cycle, lasting approximately 10 to 14 days.
- Proestrus: This is the pre-ovulatory follicular phase when the corpus luteum regresses (luteolysis) and a new dominant follicle begins to grow rapidly under FSH stimulation.
It lasts for approximately 3 to 4 days.
Therefore, estrus is the shortest phase, and diestrus is the longest phase.

Step 3: Final Answer:
In cows, the phases of the oestrus cycle of shortest and longest duration are oestrous and dioestrus, respectively.