Comparative evaluation of a commercial Tritrichomonas foetus vaccine in infected and uninfected bulls and heifers during a 45-day natural breeding season.

Tritrichomonas foetus is a venereal protozoan parasite that causes significant reproductive losses in cattle. Bulls act as asymptomatic carriers, transmitting the pathogen to susceptible cows, leading to infertility, embryonic or fetal loss, and other reproductive disorders. With no FDA-approved treatments available, vaccination has become a key control strategy. This study evaluated the reproductive effects of a commercially available killed, whole-cell vaccine (TrichGuard®) administered to both heifers and T. foetus-positive bulls in a natural mating system. Heifers and bulls were randomly assigned to one of four vaccine treatment groups. Pregnancy status was monitored, and statistical models assessed pregnancy maintenance and loss. A significant treatment effect was observed on the probability of maintaining pregnancy (P = 0.03), with control (uninfected) heifers showing the highest odds of retention. Vaccinated and infected groups all showed reduced odds of maintaining pregnancy, though post hoc comparisons showed no significant differences amongst any of the vaccination protocols. Pregnancy loss did not differ significantly between groups (P = 0.22). Survival analysis revealed a treatment effect (P = 0.04), driven by the absence of pregnancy loss in the control group. These findings suggest that vaccination with the commercially available vaccine Trichguard® may have variable efficacy in reducing reproductive losses in the face of natural infection.