What is the typical duration of the bovine estrous cycle?

• A. About 14 days.
• B. About 21 days.
• C. About 28 days.
• D. About 35 days.

Answer: (B)

The typical duration of the bovine estrous cycle is about 21 days. This comes from two main phases: a luteal phase lasting roughly 14 days, when the corpus luteum produces progesterone, and a shorter follicular phase lasting about 5 to 7 days leading up to ovulation. When the cow does not conceive, luteolysis ends the luteal phase and starts a new cycle, returning to the follicular phase and ovulation about three weeks later. There is natural variation, with cycles usually in the range of 18 to 24 days, but 21 days is the standard figure used in practice. Other lengths like around 14 days, 28 days, or 35 days do not typically describe bovine cycles.