Effect of a multivalent vaccination protocol on reproductive efficiency in Bos indicus beef females

The aim of this study was to evaluate the effect of a multivalent reproductive vaccination program against BoHV-1, BoHV-5, BVDV-1, BVDV-2, Leptospira spp., and Campylobacter fetus on the reproductive performance of 1217 beef cows and heifers (Bos indicus) subjected to two consecutive timed artificial insemination protocols (TAI). Serological titers for BoHV-1, BVDV, Leptospira spp., and Neospora caninum were analyzed before vaccination. The first dose of the multivalent vaccine was administered 21-30 days before the TAI protocol, with a booster on day 0 (D0). Artificial insemination (AI) occurred 11 days later (D11). Pregnancy diagnosis was performed by ultrasonography 28-30 days after TAI and confirmed at 120 days by transrectal palpation. At 120 and 210 days of gestation, previously vaccinated females received a booster dose containing only Leptospira spp. antigens. All females were monitored until birth, to calculate the calving rate of the inseminated animals. High pre-vaccination seroprevalence was observed for all tested agents, indicating widespread prior exposure within the herd. No significant differences in pregnancy per AI (P/AI) were detected between vaccinated and control groups after the first TAI. However, higher P/AI at 120 days and lower pregnancy loss was observed between 30 and 120 days (P = 0.03) in vaccinated animals after second TAI. These findings indicate that multivalent inactivated reproductive vaccination is safe and may contribute to the immunological stability of naturally exposed herds. However, its impact on immediate fertility appears to be limited, particularly in populations with high pre-existing immunity.