Prostaglandin treatment will cause degeneration of the corpus luteum in cow ovaries. Some cows' corpus luteum responds to prostaglandins 5-6 days after estrus, but most cows only respond to prostaglandins 7-8 days after estrus. When observed on B-ultrasound in cows, the corpus luteum of the treated cows begins to shrink in volume.

When processed in the late stage of the estrus cycle, such as 17 days of estrus, the corpus luteum in the cow's ovaries will regress by the prostaglandins secreted by itself, and the shape of the corpus luteum is almost invisible on ultrasound in cows.

The time from prostaglandin treatment to ovulation is determined by the physiological condition of the follicles. When cows are treated with prostaglandin 6 days after estrus, the dominant follicle of the first follicle wave continues to develop. Therefore, the average time from prostaglandin treatment to ovulation is 3 days. The development process of follicles can be seen on ultrasound in cows.

When cows are in estrus for 13 days and treated with prostaglandins, they are in the early stage of dominant follicle development in the second follicle wave. Therefore, the average time from prostaglandins treatment to ovulation is 3.5 days; When most cows are treated with prostaglandins 9 days after estrus, the average ovulation time of the dominant follicle formed by the first follicle wave is on the 4th day after prostaglandins treatment. However, some cows are in the early stage of the dominant follicle in the second follicle wave when they are treated with prostaglandins 9 days after estrus. Therefore, it takes 6 days for the dominant follicle in the second follicle wave to mature and ovulate. Prostaglandin treatment affects the pregnancy rate of cows at different stages of the estrus cycle.

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