Effect of hCG Administration at the Second Cloprostenol Injection on the Reproductive Performance of Saanen Goats Previously Exposed to 16‐h Photoperiod

This study aimed to evaluate the effects of human chorionic gonadotropin (hCG) on the second prostaglandin F2α (PGF2α) injection in anestrous Saanen goats that had been previously exposed to a 16‐h photoperiod. Seventy‐two pluriparous goats were subjected to a 16‐h photoperiod for 60 days. Ten days later, synchronisation of estrus was conducted with two injections of cloprostenol administered 11.5 days apart. At the second injection, goats received either 300 IU of hCG (hCG group) or no hCG (control group). Estrus response, ovarian structures, progesterone (P4) concentrations, and pregnancy rates were assessed. Estrus response after the second cloprostenol injection (70.8%; 51/72) was higher ( p < 0.05) than that of the first injection (39.0%; 28/72; p < 0.05). Goats in the hCG group ovulated earlier ( p < 0.05; 45.0 ± 5.9 h) compared with the control (72.9 ± 4.8 h), with a shorter interval between estrus and ovulation (−1.2 ± 7 h vs. 34.2 ± 3.3 h; p < 0.05). Although hCG increased the luteal area and P4 concentrations, pregnancy rate was drastically reduced ( p = 0.05) in the hCG group (25.0% vs. 47.2%). Moreover, hCG reduced ( p < 0.05) the incidence of premature luteal regression (11.1% vs. 30.6%). No differences were observed in follicular number or diameter between groups. It was concluded that even though hCG effectively induced ovulation and enhanced luteal function in goats during anestrus, its administration in conjunction with the second PGF2α injection may have excessively advanced ovulation, impairing estrus–ovulation synchrony, which markedly reduces pregnancy rate. Timings of hCG administration should be further explored to optimise its reproductive benefits without compromising pregnancy outcome.