Comparison of the effect of Gonadotropin-Releasing Hormone and Human Chorionic Gonadotropin on Reproductive Performance of Romanov Ewes during the Natural Breeding Season

Low pregnancy rate is an important issue in small ruminants. Superovulation protocols would serve as the possible techniques to increase the pregnancy rate in small ruminants due to the use of synthetic hormones. The present study aimed to assess the effect of gonadotropin-releasing hormone (GnRH) and Human chorionic gonadotropin (hCG) after artificial insemination (AI) on the pregnancy rate of Romanov ewes breed. To this end, estrus was synchronized in 140 ewes using a controlled internal drug-releasing (CIDR) device. Following CIDR removal, all ewes received 400 IU Pregnant Mare's Serum Gonadotropin (PMSG). The ewes were assigned to three groups (control, n=20; experimental groups, each of them was divided into three subgroups, n=20). The first group in each experiment was assumed as control. The second and third groups received three levels of GnRH, (400, 500, and 600 μg, n=20) and hCG (200, 300, and 400 IU) administered by the intramuscular (IM) route. As soon as the signs of estrus were observed, the ewes were isolated from the others and artificially inseminated with fresh sperm using the transcervical method. The results indicated that there were no significant differences between experimental groups in ovulation and pregnancy rates on days 33 and 90 post-AI (P>0.05). The highest twin birth rate (20%) was recorded in the hCG group (300 IU), as compared to GnRH and control groups (P<0.05). The effect of GnRH and hCG on the plasma concentration of progesterone was significant (P<0.01). The groups significantly differed in fecundity rate (Single birth, twin birth, and triple birth) (P<0.05), all of these parameters were significantly higher in the hCG 300 IU group. It can be concluded that the injection of 300 IU of hCG hormone after insemination improves pregnancy rate in ewes.