Effects of early vaccination with Improvac® on the development and function of reproductive organs of male pigs

Gonadotropin-releasing hormone (GnRH) vaccine (Improvac®) is effective at diminishing boar taint by interfering with testis function. Early pre-pubertal vaccination at 10 and 14 weeks-of-age could be desirable if sufficient and sustained effects could be achieved. Crossbred male pigs (n = 24) were randomly assigned to three groups each with eight individuals: an unvaccinated control group, one group vaccinated with Improvac® early at ages 10 and 14 weeks, and a third group vaccinated with Improvac at the standard ages of 16 and 20 weeks. The average age at slaughter was 25 weeks. At slaughter, reductions in testes weight and bulbourethral gland length of vaccinated pigs compared with controls were observed (P < 0.001), accompanied by lowered testosterone concentrations in peripheral blood (P < 0.001). The diameter of tubuli seminiferi was affected; being 18% smaller in standard and 38% smaller in early vaccinated males, compared with controls (P < 0.01). Leydig cells in vaccinated pigs became pycnotic, and their number decreased in early vaccinated pigs. Spermatogenesis was disrupted, evidenced by spermatocyte loss among standard vaccinated pigs to severe spermatogenic arrest among early vaccinated pigs. This histological picture was reflected in the absence of epididymal spermatozoa in 5 of 8 early vaccinated pigs and a dramatic reduction in the remaining 3 early vaccinated pigs. Among standard vaccinated pigs, 5% of the spermatozoa were morphologically normal (>70% in controls, P < 0.01). Early vaccination caused a more severe disruption of testicular structure and function than standard vaccination, thus providing an alternative for immunocastration of male pigs.