Field Implementation of Buserelin-Supplemented Boar Semen Protocol at the First Insemination: Farrowing Rate and Litter Size in Gilts and Sows Under Tropical Conditions

Maximizing farrowing rate and litter size is essential for improving reproductive efficiency and profitability in swine production. Both outcomes depend on the timing of artificial insemination (AI) relative to ovulation; however, predicting ovulation is challenging because estrus duration and the interval from estrus onset to ovulation vary considerably among females. Therefore, this study aimed to determine whether supplementing extended boar semen with 4–8 µg of buserelin acetate at the first insemination improves the reproductive performance of gilts and sows under tropical commercial conditions. A randomized controlled field trial was conducted involving 2780 Landrace × Yorkshire females across five commercial herds in tropical regions (herds A–E). The females (parity 3.0 ± 2.1) comprised gilts (n = 412), sows (n = 2280), and repeat-service females (n = 88). They were randomly assigned to receive either standard extended semen (control; n = 1438) or extended semen supplemented with 4 μg (1.0 mL; n = 121), 5 μg (1.25 mL; n = 1052), or 8 μg (2.0 mL; n = 169) of buserelin acetate per 90 mL insemination dose (treatment; n = 1342). The overall farrowing rate was 88.5% and ranged from 84.5% to 90.0% among herds. Buserelin supplementation increased the farrowing rate compared with the control (90.1% vs. 86.9%, p = 0.009), representing an improvement of 3.2 percentage points. In Herd C, supplementation increased the farrowing rate from 86.5% to 90.1% (p = 0.036). The overall total number of piglets born was 14.1 ± 3.2 per litter. Litter size did not differ significantly between groups in any herd (all p > 0.05), although buserelin-treated females generally had numerically more total-born and live-born piglets. Among gilts, buserelin tended to increase the total number born (12.7 ± 0.4 vs. 11.8 ± 0.4 piglets, p = 0.083), but not the number born alive (11.3 ± 0.4 vs. 10.6 ± 0.4 piglets, p = 0.258). No significant effects were observed in sows for total-born or live-born piglets (+0.3 and +0.4 piglets, p = 0.380 and 0.376, respectively), or in repeat-service females (−0.4 and +0.2 piglets, p = 0.735 and 0.883, respectively). These findings indicate that supplementing extended semen with buserelin acetate at the first insemination is a practical, non-invasive strategy for improving farrowing success in commercial swine herds under tropical conditions. Further studies should clarify the underlying endocrine and reproductive mechanisms and identify the physiological or reproductive characteristics of females most likely to benefit from additional hormonal stimulation.