Luteogenesis and Embryo Implantation Are Enhanced by Exogenous hCG in Goats Subjected to an Out-of-Season Fixed-Time Artificial Insemination Protocol

SIMPLE SUMMARY: In temperate and subtropical ecosystems, goats are classified as seasonal-polyestrous, generating a seasonality in their products (i.e., milk, meat). In order to abolish or reduce this reproductive seasonality, exogenous hormones, such as human chorionic gonadotropin (hCG), have been used to stimulate the development of ovarian follicles, triggering ovulation, corpus luteum formation, while increasing serum progesterone levels, fetal growth, prolificacy, and kidding rate. We tested the possible effect of two doses of hCG (i.e., 100 vs. 300 IU) in the improvement of the luteal function and embryo implantation in anovulatory goats subjected to an estrus induction protocol, and then, to a fixed-time artificial insemination protocol (FTAI). The highest values for fecundity rate, corpus luteum area, as well as embryonic efficiency index 1, were favored in goats treated with 300 IU hCG 14 days post-artificial fertilization. The embryonic efficiency and the index embryonic implantation efficiency were favored in goats treated with 300 IU hCG 7 and 14 days post-artificial insemination. This work contributes to explore the most suitable use of exogenous hormones that favor the out-of-season reproductive outcomes in goats and to boost the embryo implantation efficiency. ABSTRACT: The aim of this study was to evaluate the possible effect of two doses of hCG (100 and 300 IU) applied at two different times (7 and 14 d) after a fixed-time artificial insemination protocol (FTAI) upon some variables involved in the embryonic implantation rate in goats during the natural deep anestrous season (April, 25° north). The experimental units considered crossbred, multiparous, anovulatory goats (n = 69, Alpine, Saanen, Nubian x Criollo), with average body weight (43.6 ± 5.7 kg) and body condition score (1.86 ± 0.28 units) located in northern–semiarid Mexico (25° N, 103° W). Once the goat’s anestrus status was confirmed, goats were subjected to an estrus induction protocol. Upon estrus induction confirmation, goats (n = 61) were subjected to a FTAI procedure. Immediately after the FTAI, the goats were randomly distributed to five experimental groups: (1). G100-7 (n = 13) 100 IU, hCG 7 d post-FTAI, (2). G100-14 (n = 12) 100 IU hCG, 14 d post-FTAI, (3). G300-7 (n = 12) 300 IU, hCG, 7 d post-FTAI, (4). G300-14 (n = 12) 300 IU hCG 14 d post-FTAI, and (5). Control group, CONT (n = 12) 0.5 mL saline, 7 and 14 d post-FTAI. The response variables conception rate (39.36 ± 0.23), fertility rate (27.96%), prolificacy rate (1.1 ± 0.29 kids), ovulation rate (0.74 ± 0.20 corpus luteum) corpus luteum diameter (10.15 ± 0.59 mm), embryo number (1.58 ± 0.20), and embryo implantation rate (48.96%), did not differ between treatments. However, while the variables fecundity rate (67%), embryo efficiency index-1 (33.99 ± 0.20%), and embryo efficiency index-2 (27.94 ± 0.30%) were favored by the G300-14 treatment, the corpus luteum area was favored (p < 0.05) by both G300-7 (113.30 ± 0.19 mm(2)) and G300-14 (103.04 ± 0.17 mm(2)). Such reproductive strategy emerges as an interesting approach, not only to enhance the out-of-season reproductive outcomes, but also to boost one of the main rulers defining the global reproductive efficiency of a heard, namely, the embryo implantation efficiency.