Abstract: This paper aims at studying the recovery of the uterus and the change of the ovary in postpartum dairy cows by ultrasonography scanning and researching on the variation of the reproductive performance, in order to supply datum for better guiding postpartum breeding and reproduction of dairy cows. On experiment plan, Choose 8 heads of Chinese postpartum dairy Holstein (including 4 heads of primiparous and 4 heads of multiparous dairy cows). The recovery of the uterus and the change of the ovary in postpartum dairy cows were studied by ultrasonography from the first day of postpartum last to the time of the next estrus mating. The results showed that the recovery times of cervix and uterine wall in primiparous dairy cows are about 25 days and 32 days respectively, in multiparous dairy cows are all about 27 days. The development of the follicles in primiparous and multiparous dairy cows all experienced six follicle waves, the first three follicle waves being one estrous cycle and the last three follicle waves being one estrous cycle. Because the uterus did not recover completely, the mating should be at the end of the second estrous cycle(that is at the time of the sixth follicle wave).The average time of postpartum estrus mating in primiparous and multiparous dairy cows are about 90 days and 53 days respectively. All results mentioned above indicated that the average time of cervix recovering to normal in primiparous dairy cows is 2 days earlier than that of the postpartum dairy cows, but the average time of uterine wall recovering to normal in primiparous dairy cows is 5 days later than that of the postpartum dairy cows, the average time of estrus mating in primiparous dairy cows is 37 days later than that of the postpartum dairy cows.

Key words: dairy cow; uterus; ovary; B ultrasonography; postpartum recovery