The prostaglandin treatment will degenerate the corpus luteum in the cow’s ovary. The corpus luteum of some cattle responds to prostaglandins 5-6 days after estrus, but most cattle do not respond to prostaglandins until 7-8 days after estrus. When observed on a B-ultrasound for cattle, the treated cow’s corpus luteum began to shrink in volume.When processed at the late stage of the estrus cycle, such as the 17th day of estrus, the corpus luteum in the cow’s ovary will degenerate by the prostaglandin secreted by itself, and the shape of the corpus luteum is almost invisible on the B-ultrasound.The time from prostaglandin treatment to ovulation is determined by the physiological condition of the follicles. When a cow is treated with prostaglandin 6 days after estrus, the first follicular wave dominant follicle continues to develop, so the average time from prostaglandin treatment to ovulation is 3 days. The development of follicles can be seen on B-ultrasound for cattle. When the cow is treated with prostaglandin 13 days after estrus, it is in the early stage of the second follicular wave dominant follicle development, then the average time from prostaglandin treatment to ovulation is 3.5 days; most cows are 9 days after estrus prostaglandin During treatment, the average ovulation time of the dominant follicle formed by the first follicle wave was the 4th day after prostaglandin treatment. When some cattle are treated with prostaglandin 9 days after estrus, the dominant follicle of the second follicular wave has just begun, so it takes 6 days for the dominant follicle of the second follicular wave to mature and ovulate. Prostaglandin treatment at different stages of the estrus cycle affects the pregnancy rate of cows

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