Ovulation Timing After Recombinant Human Chorionic Gonadotropin, Gonadorelin, or Buserelin Under Estrus-Triggered and Fixed-Time Treatment Protocols for Artificial Insemination in Sows

Precise coordination between ovulation and insemination is essential for optimizing fixed-time artificial insemination (FTAI) in sows. This study compared ovulation timing and reproductive outcomes after treatment with recombinant human chorionic gonadotropin (rhCG), gonadorelin, or buserelin under estrus-triggered and fixed-time treatment protocols. A total of 285 sows received equine chorionic gonadotropin 24 h after weaning. In Trial 1, the ovulation-inducing treatments were administered at estrus onset, whereas in Trial 2 they were administered 72 h after equine chorionic gonadotropin. Ovulation was monitored by transabdominal ultrasonography. In Trial 1, no significant differences in ovulation timing or reproductive performance were detected among treatments. In Trial 2, no significant differences were detected among treatments in the proportion of sows with ovulation detected within 72 h (p = 0.847), the overall time-to-event distributions (log-rank p = 0.790), or the variability in detected ovulation timing (Brown–Forsythe p = 0.884). Among rhCG-treated sows in which ovulation was detected, all observed ovulations occurred between 37 and 54 h after treatment. No statistically significant differences in reproductive outcomes were detected among treatments. These findings provide new information on the temporal ovulatory response to rhCG under fixed-time treatment and may inform further refinement of insemination timing in sow FTAI protocols.