Ovarian Response and Fertility after Short-Term Progestagen/eCG Treatments Are Compromised in Nulliparous Sheep during Non-Breeding Season

SIMPLE SUMMARY: The application of treatments based on controlled dose progesterone intravaginal devices (CIDR) plus equine chorionic hormone (eCG) has been favored in recent years for the induction and/or synchronization of estrus activity and ovulation in the breeding and the non-breeding seasons. In anestrous mature ewes, short-term treatments are equally effective as long-term treatments, but information on the effects of such treatments for maiden sheep is scarce. ABSTRACT: The objective of this investigation was to determine the ovarian response, fertility, and prolificacy of nulliparous sheep when compared to multiparous sheep after a short-term (7 days) CIDR/eCG treatment which was administered during the non-breeding season. All the multiparous sheep, whereas only 54% of the nulliparous ewes, showed signs of estrus. However, 81.8% of the multiparous sheep and 100% of the nulliparous ewes ovulated. Fertility was also low after short-term progesterone treatments during the anestrous season in maiden sheep (30.8 vs. 72.7% in multiparous ewes). Such results indicate significant differences in the response to CIDR/eCG protocols for induction and synchronization of estrus and ovulation between nulliparous and multiparous sheep during the non-breeding season.