Efficiency of hCG for Inducing Resumption of Ovarian Cyclicity and Synchronized Ovulations during the Seasonal Anestrous in Sheep

SIMPLE SUMMARY: The use of equine chorionic gonadotrophin (eCG) in protocols for estrus synchronization in sheep is currently challenged, so it is necessary to implement alternatives (i.e., human chorionic gonadotropin; hCG), mainly during the anestrous season. Therefore, we compared the reproductive outcomes, including estrus induction, ovulatory follicle dynamics, and pregnancy outputs in anestrus Dorper sheep treated with insertion of one intravaginal progesterone-loaded CIDR + either saline, eCG, or hCG. The administration of hCG at the time of CIDR removal was effective at inducing estrus, resume ovulations, and ovarian cyclicity, yet, in a narrow window of time, it is a scenario that may limit the implementation of an artificial insemination protocol. ABSTRACT: This research aimed to evaluate whether the administration of hCG at the time of removal of a progesterone device may be effective at inducing estrus and ovulations in sheep during the natural seasonal anestrous, by comparing reproductive outputs (induction and duration of estrus, follicle development, ovulation, ovulation rate, and pregnancy rates) in ewes treated with eCG or only saline solution at the time of CIDR removal. Whereas results demonstrated no response in the control non-treated group, the largest rate of narrowly synchronized estrus signs and ovulations occurred in the eCG-group. The administration of hCG was effective at inducing estrus, promote follicular growth and a delayed yet significant ovulation (>84%) on day 10 after CIDR removal; moreover, an increased embryonic implantation rate was also observed. Moreover, if the hCG ewes remain exposed to active males for some days, said strategy could be adopted, aiming to induce pregnancies by natural mating in a short period of time.