During Metoestrus I, which is true?

• A. Metoestrus I lasts for approximately 20 days
• B. Behaviour returns to normal
• C. Vulva reduces in size
• D. Corpus Luteum continues to secrete Progesterone

Answer: (D)

The main idea here is that metoestrus is a luteal phase driven by the corpus luteum, which continues to produce progesterone. After ovulation, the corpus luteum forms and secretes progesterone to keep the uterine lining prepared for possible pregnancy and to regulate the cycle. This ongoing progesterone secretion is what defines metoestrus, so the statement that the corpus luteum continues to secrete progesterone is true.

Other options aren’t as reliable. The length of metoestrus I isn’t a fixed 20 days across species, so a specific duration isn’t universally correct. Behavioural changes can persist beyond metoestrus as hormones influence activity, so returning to normal isn’t guaranteed right away. Vulval size changes are most pronounced earlier in the cycle (like proestrus) and aren’t a definitive feature of metoestrus I.