Researchers tested two experimental GnRH vaccines in male piglets and compared them to a commercial vaccine and surgical castration. Both new vaccines generated strong antibody responses, but they didn't lower testosterone or shrink testicles as much as the commercial product, meaning they were less effective at acting as a contraceptive in this animal model.

This study assessed the contraceptive effects of two vaccines formulated with recombinant gonadotropin-releasing hormone antigen (rGnRH antigen) conjugated with the heat-labile enterotoxin B subunit (LTB) protein from Escherichia coli in male pigs. Thirty-two piglets were assigned to four groups: Surg, surgically castrated at 3 days old; Vvx, non-castrated and vaccinated with a commercial vaccine (Vivax®) at 101 and 135 days old; rGnRH-400 and rGnRH-300, non-castrated and vaccinated at 101 and 135 days old with recombinant vaccines containing 400 µg or 300 µg rGnRH/LTB per dose, respectively. Growth performance was not affected by treatment (p ≥ 0.25). At 155 and 165 days old, piglets in the rGnRH-400 and rGnRH-300 groups exhibited anti-GnRH/LTB antibody levels were similar to those in the Vvx group (p > 0.05) or higher (p < 0.05) than those in the Vvx group. However, rGnRH-400 and rGnRH-300 piglets showed higher testosterone concentrations at 155 and 165 days old and greater testicular volumes at 165 days old than Vvx piglets (p < 0.05). Severe testicular lesions (scores 3 and 4) were more frequent in the Vvx group, while those in the rGnRH-400 group were mainly scored as 3, and only mild lesions (scores 1 and 2) were observed in the rGnRH-300 group. Overall, both recombinant vaccines elicited strong anti-GnRH/LTB antibody levels; however, they did not produce the same degree of testicular alterations or testosterone reduction as the commercial vaccine. Further studies are warranted to evaluate the contraceptive potential of these recombinant formulations, particularly the 400 µg rGnRH/LTB vaccine.