This study compared the effects of a dose of human chorionic gonadotropin (hCG) administration at the time of insemination on the reproductive outcome of estrus-synchronized Mongolian ewes subjected to two artificial insemination methods during the breeding season. All females were treated with a polyurethane intravaginal sponge impregnated with 45.00 mg of flurogestone acetate for 12 days, followed by an intramuscular injection of 330 IU of equine chorionic gonadotropin at sponge removal. In Experiment 1, 150 ewes were inseminated using a laparoscopic intrauterine artificial insemination method 48 hr after sponge removal. The ewes were randomly assigned to the hCG group which received 500 IU of hCG at the time of insemination, and the control group which received 1.00 mL of sterile saline solution. In Experiment 2, 85 ewes were inseminated twice at 48 and 60 hr after sponge removal using a cervical artificial insemination method. The ewes were randomly assigned to the hCG group, which received 500IU of hCG at the time of the first insemination and the control group which received 1.00 mL of sterile saline solution. The pregnancy rate in the control group was not significantly different compared to the hCG group in Experiment 1 and the pregnancy rate in the control group was significantly higher compared to the hCG group in Experiment 2. In conclusion, the administration of hCG at the time of insemination could not be recommended in ewes when implementing a fixed time artificial insemination protocol during the breeding season.
Zhang et al. (Wed,) studied this question.