162 DEVELOPMENT AND EVALUATION OF AN ORAL CONTRACEPTIVE BAIT FOR FERAL PIGS

Abstract

Feral pigs (Sus scrofa) are an invasive species widely distributed throughout North and South America, as well as Australia. Feral pigs frequently destroy farm fields, causing $1.5 billion in damage annually in the United States alone. These pigs are known carriers of over 30 diseases, thereby posing a threat to livestock and public health. Current control methods are ineffective due to high fecundity rates. An orally consumed contraceptive bait may be effective, but currently none exists for pigs. In rats, an orally consumed contraceptive that affects both male and females has shown considerable promise. This bait contains 2 active ingredients: triptolide, a diterpenoid diepoxide isolated from the Chinese medicinal plant Tripterygium wildfordii, and 4-vinylcyclohexene diepoxide (VCD), an industrial chemical. Triptolide prevents ovarian follicle maturation and disrupts spermatogenesis; VCD acts in the female to cause premature ovarian failure and, in one report, disrupt male mouse spermatogenesis. There are no studies reported for these active ingredients on boar spermatogenesis. A proprietary pig bait has been developed containing these 2 ingredients and was fed to commercial (com.) and Sinclair (sin.) boars (com. n = 3, sin. n = 3) for 15 consecutive days to evaluate changes in reproductive parameters. Boars were given 250 g of bait twice daily that contained 0.25 mg of triptolide and 1.55 mM of VCD. Ejaculates were collected from boars before, during, and after the treatment period (Day 0, 7, 15, 30, 37, 45, and 60) and were evaluated for possible impacts on fertility. Ejaculates were able to be collected from 4 of 6 boars (com. n = 2, sin. n = 2). Previous studies indicate triptolide acts during the differentiation phase of spermatogenesis, suggesting a delayed onset of perturbation allowing for comparison of semen collected early in the study (Day 0, 7, and 15) to post-treatment samples. Progressive motility (PM) was rated on a 1 to 5 scale. Plasma testosterone and testes volume were also monitored at these time points. Statistical analysis was performed using Kruskal–Wallis test. No significant differences were found in plasma testosterone, testes volume, or sperm concentration. No significant differences in viability, morphology, or PM were found at Day 0, 7, or 15. However, differences (P < 0.05) were observed in semen parameters at Day 37 and 45 in comparison to D0, 7, and 15. The percentage of sperm with normal morphology at treatment Day 37 (3.3%) and 45 (3.3%) was lower than at Day 0, 7, and 15 (72.3%, P < 0.05). Differences (P < 0.05) were also found in viability at Day 37 (13.3%) and 45 (8%) in comparison to Day 0, 7, and 15 (71.6%). Differences were also found in PM at Day 37 (0.33) and 45 (1) in comparison to Day 0, 7, and 15 (4.8). These results suggest an impact on spermatogenesis, specifically spermiogenesis, suggesting a decrease in fertility due to lower quality of spermatozoa. Further studies are needed to evaluate the bait’s impact on feral pig reproduction.