Veterinary Research Forum

Abstract Although equine chorionic gonadotropin (eCG) combined with gonadotropin-releasing hormone (GnRH) is known to improve reproductive rates by increasing the numbers of ovulating oocytes, the actions of these hormones on embryo implantation have not been elucidated. We herein eliminated the effects of embryos by performing embryo transfer and elucidated the effects on embryo implantation after hormonal treatment. The recipient mice were allocated to four groups, including control, eCG, GnRH, and eCG + GnRH groups. Well-developed blastocysts were transferred into recipients, and implantation sites were counted five days after embryo transfer. Our results revealed that embryo implantation rates in the eCG and eCG + GnRH groups were significantly lower than GnRH and control groups; eCG and eCG + GnRH groups didn’t differ, and the implantation rate was the lowest in the eCG + GnRH group. When we evaluated estrogen and progesterone concentrations in four groups on embryonic day 0.5 to embryonic day 3.5, we noted that serum estrogen levels in eCG + GnRH group were significantly higher than the other groups, while progesterone levels were significantly lower than the control group, and that the progesterone/estrogen ratio was significantly reduced relative to the control group. Finally, the expression of the endometrial receptivity-related Lif gene was significantly diminished in the eCG + GnRH and eCG groups compared to the other groups. These results suggest that eCG combined with GnRH as a super-ovulatory regimen reduced mouse embryo implantation rates via an estrogen-mediated impairment of endometrial receptivity.

Abstract 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.