Abstract

Simple Summary Low reproductive performance during anestrus restricts the potential for year-round sheep production in temperate areas, precisely when food security is urgently demanded. Hormonal strategies used to improve this performance have largely relied on progesterone and equine chorionic gonadotropin (eCG). The last is a hormone obtained from the blood of pregnant mares that promotes follicular development (FSH activity in ruminants). However, recent information assigns LH, instead of FSH, the essential role of driving this development to ovulation. Therefore, we assessed this possibility using human chorionic gonadotropin (hCG) in anestrous sheep. The last has specific LH activity and is obtained from gestating woman urine. In this study, we showed that the fundamental restriction for better reproductive output during anestrus is a limitation not in the number of follicles but in their functional competence for ovulation. We also showed that a single administration of hCG seems as effective as eCG in promoting follicular development, ovulation, and fertility in sheep, provided that the hCG dose is appropriate. Our results could lead to better reproduction output during anestrus in sheep.Abstract The study tested the hypothesis that a single administration of hCG supports the LH-dependent phase of terminal follicular development in synchronized sheep during anestrus, using eCG as a functional reference. Using a clinical approach, four experiments were designed to achieve the following: (1) Identify the inhibitory influence of anestrus on reproduction efficiency; (2) Assess the potential of hCG to keep functional blood concentrations after a single dose; (3) Characterize the effect of different doses of hCG on reproductive functional markers; (4) To compare the ability of hCG to that of eCG to support follicular development and fertility based on the same markers. The results showed that anestrus seems to affect follicular and luteal function under LH dependency as FSH-dependent markers are not compromised; hCG maintains higher blood concentrations than controls for at least 48 h; hCG improves follicular development and ovulatory rates compared to controls and at standards comparable to a breeding season; and ewes treated with hCG exhibit similar performance to those treated with eCG. Our results conclude that hCG can be used to support follicular function during anestrus in sheep, aiming to perfect its regulation in assisted reproduction.