A study on the effect of GnRH administration on the ovarian response of Awassi ewes treated with eCG to induce superovulation

The present study was undertaken to investigate the effect of GnRH administration on the superovulatory response of ewes treated with eCG in breeding season and nonbreeding season at the college of veterinary medicine, university of Mosul farm. Twelve nonpregnant and cycling Awassi ewes of 3-4 years of age were randomly allocated in equal number (n= 6) to two groups. Each ewe was treated with a progesterone impregnated intravaginal sponge for 12 days. The following superovulation treatment was used; Ewes of group 1 received 1200 IU of eCG once as an intramuscular injection48 h prior to sponge withdrawal. Ewes of group 2 were also received 1200 IU of eCG once as an intramuscular injection 48 h prior to sponge withdrawal and after 24 h of sponge removal ewes were injected with 80 μg of GnRH. Ewes standing to be mounted were recorded as in estrus and mated at least two times with Awassi rams of proven fertility. Ovarian response was assessed by determining number of corpora lutea by laparoscopy on day 6 after mating. Embryo recovery was performed by semilaparoscopic and by flushing both uterine horns. Results of the present study showed when ewes treated in breeding season the number of corpora lutea was significantly higher (P 0.05) in ewes treated with eCG plus GnRH than eCG alone as 7.33±0.54 and4.33±0.39, respectively. There was no significant difference in the number of corpora lutea in non-breeding season when ewes treated with eCG and eCG plus GnRH. High number (P 0.05) of unovulated follicles was observed in ewes treated with eCG in breeding season and non-breeding season as 2.45±0.25 and 1.16±0.3, respectively. Number of recovered embryos from ewes treated with eCG plus GnRH and eCG differ significantly (P 0.05) as 4.32±0.56 and 2.66±0.66, respectively in the breeding season. While no significant difference was observed when these hormones used for superovulation in the non-breeding season. It could be concluded that administration of GnRH 24 h after sponge removal increased ovulation rate of Awassi ewes treated with eCG for superovulation in the breeding season