Optimization of artificial insemination in swine through GnRH agonist application in boar semen with special emphasis on epithelial penetration and pharmacokinetics

Induction of ovulation in pigs is a widely applied technique in commercial swine farms, using hormonal treatments to improve reproductive efficiency and productivity. The GnRH agonist buserelin acetate is widely used to induce ovulation and can be administered via intramuscular or intravaginal routes. However, the success of ovulation induction via the intravaginal route still depends on several factors, and information regarding the pharmacokinetics and tissue permeation of buserelin remains limited. This thesis aimed to investigate the pharmacokinetic profile, endometrial permeability, and reproductive effects of buserelin to develop an effective and practical ovulation control strategy for commercial swine production. This thesis comprised three parts as follows: i) To determine the pharmacokinetic and bioavailability characteristics of buserelin following intramuscular administration in prepubertal gilts. Ten gilts underwent surgical implantation of an indwelling venous catheter to allow repeated blood samplings for pharmacokinetic assessment. Buserelin was rapidly absorbed and eliminated, with an average maximum plasma concentration (Cmax) of 2.21 ± 0.72 µg/L at 0.30 ± 0.10 h (Tmax) and a short elimination half-life (T½) of 0.51 ± 0.03 h, indicating fast metabolism and clearance. ii) To investigate the in vitro permeability of buserelin through porcine endometrial tissue using the vertical Franz diffusion cell system as a model for drug absorption across reproductive membranes. Approximately 60% of buserelin permeated through endometrial tissue within 8 h in both control and treatment groups, while the semen-supplemented group showed a significantly higher permeation rate during the first 1.5 h (P < 0.001), suggesting enhanced diffusion dynamics when combined with diluted semen. iii) To evaluate the effects of supplementing extended boar semen with buserelin on reproductive performance of gilts and sows. A total of 741 pigs were randomly assigned to four groups: control, 10-IM (10 μg of buserelin i.m.), 5-S (semen + 5 μg of buserelin), and 10-S (semen + 10 μg of buserelin). The average farrowing rate was 88.9%, with 17.0 ± 4.0 total and 15.2 ± 3.5 live-born piglets per litter. No significant differences in conception or farrowing rates were observed among treatments. However, gilts inseminated with semen containing 5 μg buserelin (5-S) showed higher total and live-born litter sizes and greater litter weight (24.5 ± 2.0 vs. 19.4 ± 0.7 kg; P = 0.018), whereas no significant improvements were observed in sows. In conclusion, supplementation of buserelin in boar semen during artificial insemination significantly enhanced reproductive performance in pigs, particularly increasing total and live-born litter sizes and litter weight. These findings are consistent with the permeation study, which confirmed that intravaginal administration of buserelin allows effective absorption through the endometrial tissue. Pharmacokinetic results indicated that buserelin has a short half-life; therefore, administration should be timed to coincide with the estrus period for maximum effectiveness. Overall, supplementing buserelin in semen represents an effective and practical approach to improving reproductive efficiency in pigs.