Endocrine and follicular mechanisms underlying ovulation induction: A comparative study of human chorionic gonadotropin and buserelin acetate in Marwari mares

Accurate prediction of ovulation in mares is constrained by the prolonged and variable estrus period, necessitating the use of pharmacological agents to synchronize ovulation for efficient breeding management. This study evaluated the comparative efficacy of human chorionic gonadotropin (hCG) and a gonadotropin-releasing hormone analogue (buserelin acetate) for inducing ovulation in Marwari mares. A total of 210 estrous cycles from 21 mares subjected to artificial insemination with frozen semen were analyzed. Ovarian dynamics were monitored daily באמצעות transrectal ultrasonography to assess follicular development, uterine edema, and ovulatory events. Mares exhibiting grade II uterine edema and a dominant follicle ≥35 mm were assigned to one of three treatments: normal saline (control), buserelin acetate (40 µg), or hCG (1500 IU). Insemination was performed at an appropriate interval prior to ovulation, and pregnancy was diagnosed on days 15 and 30 post-ovulation. Both hCG (46.46±2.64 h) and buserelin (48.97±3.07 h) significantly reduced the interval from treatment to ovulation compared to controls (92.45±5.67 h; P<0.05). The majority of ovulations in treated mares occurred between 37 and 46 h post-administration. Ovulation within 36 h was observed in 46.6% and 38.3% of mares treated with hCG and buserelin, respectively. Hormonal treatments also shortened estrus duration relative to controls (P<0.05). In conclusion, both hCG and buserelin acetate effectively induce timely ovulation and are comparable in optimizing breeding efficiency and conception outcomes in Marwari mares.