In dairy cow production, postpartum estrus is common. There are many factors that cause postpartum estrus in dairy cows, among which ovarian inactivity is a very important aspect. For example, if the cow does not estrus for a long time, the vaginal wall and labia mask will be pale and dry. Rectal examination shows no follicles and corpora lutea, and the size and texture are normal, the surface is smooth, and there are small corpora lutea remains on some parts. If there is still no change after rectal examination after 7 to 10 days, it can be determined that the ovary is inactive.

The changes in milk progesterone in ovarian inactive cows from 7 to 85 days after delivery are consistently below 1.7ng/ml, between 0.6 and 1.7ng/ml, and there is no obvious change in milk progesterone content. This shows that the milk progesterone secretion of ovarian inactive cows is at a low level. Rectal combined with veterinary B-ultrasound examination shows that there is no corpora lutea or developing follicles on the ovaries.

The progesterone content of normal estrus cows begins to increase significantly around 32 days after delivery, reaching a peak of about 3ng/ml at 36 days, and then begins to decrease to 1ng/ml at 48 days. Then the progesterone content increases again from 56 days to 66 days, and the second peak appears, with a progesterone content of about 3.1ng/ml, and then decreases to 1ng/ml until 74 days. Then the third luteal cycle occurs. According to clinical rectal combined with veterinary B-ultrasound examination records, there is obvious follicular and corpus luteum activity on the ovaries in each luteal cycle.

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