Returning of cyclicity in infertile Corriedale sheep with natural progesterone and GnRH based strategies

Abstract

Objective: To evaluate the return of ovarian cyclicity with four hormone based protocols during non-breeding season in infertile Corriedale sheep. Methods: The return to ovarian cyclicity was considered in terms of percent estrus response rate (ERR). The time of exhibition of estrus after either sponge removal or last PGF2α injection, was considered as time to onset of estrus. Infertile Corriedale ewes were randomly selected and distributed into four groups corresponding to four hormonal protocols such as PsE (intravaginal progesterone sponges for 12 days and eCG (equine chorionic gonadotropin) at 24 h before sponge removal; n = 6), GP (GnRH on day 0 and PGF2α on day 5; n = 7), GPG (GnRH on day 0, PGF2α on day 5 and second injection of GnRH on day 7; n = 7) and PsPG (Intravaginal progesterone sponges for 12 days, PGF2α and gonadotropin-releasing hormone (GnRH) respectively, at 24 h before and after sponge removal; n = 8). Results: PsPG protocol produced significantly (P 0.05) higher than GP (85.71%) and PsE (66%). Estrus was compact and more synchronized in PsPG group because 75% of ewes exhibited estrus during the first 48 h. The collective incidence of estrus (78.94%) was also maximum during the first 48 h. Conclusion: PsPG estrus induction strategy has a potential to replace eCG based protocols for returning of ovarian cyclicity in infertile Corriedale sheep.

Keywords

• Cyclicity
• Estrus response rate
• Infertile ewes
• GnRH
• Progesterone