Abstract: [Objective] To determine the optimum time of laparoscopically assisted artificial insemination in sheep treated with estrus synchronization. [Method]The ewes with normal reproductive performance and good nutritional status were selected. The progesterone sponges were placed in vaginas of the ewes for 10-14 days, and 250-330 IU of pregnant mare serum gonadotropin （PMSG） were intramuscularly injected for each ewe when the sponge was removed. For each ewe, estrus detections were conducted twice 12-24 h after sponge removal, once in the morning and another in the evening. Four experimental groups were set according to the time after sponge removal or estrus time: group 1 （n=138） was laparoscopically inseminated 46-50 h after sponge removal, group 2 （n=156） was laparoscopically inseminated 50-54 h after sponge removal, group 3 （n=275） was laparoscopically inseminated 54-58 h after sponge removal, and group 4 （n=226） was laparoscopically inseminated 30-36 h after estrus. B-ultrosonic examination was conducted 40-45 days after insemination, and the conception rate of each group was calculated. [Result] The highest conception rate （97.79%） was observed in the ewes laparoscopically inseminated 30-36 h after estrus （group 4）, followed by those laparoscopically inseminated 50-54 h after sponge removal （group 2）, which had a conception rate of 97.44%. The conception rate of the ewes laparoscopically inseminated 46-50 h after sponge removal （group 1） was 91.30%. The ewes laparoscopically inseminated 54-58 h after sponge removal （group 3） had the lowest conception rate （89.82%）. [Conclusion]For laparoscopically assisted insemination of ewes in combination with estrus synchronization, the optimum insemination time is 50-54 h after progesterone sponge removal or 30-36 h after estrus.

Key words: sheep, estrus synchronization, artificial insemination, laparoscopically assisted insemination