Influence of vaccination with a combined chemically altered/inactivated BHV-1/BVD vaccine or a modified- live BHV-1/BVD vaccine on reproductive performance in beef cows and heifers
A field trial was conducted on 10 herds of previously- vaccinated cows and heifers (n=1,567) to evaluate the reproductive effects of prebreeding vaccination with either a modified-live virus (MLV) or a chemically altered/inactivated (CA/IV] BHV-1/BVDV vaccine. Animals received a single (cows) or 2 injections (heifers) of either vaccine, with the final injection between 27 and 89 days before breeding, which consisted of timed AI following a 7-d CO-Synch + CIDR synchronization. Conception rates to AI were greater in the CA/IV vaccine group compared to the MLV vaccine group (P=0.05; 60% vs 52%). Interval from vaccination with either vaccine until AI also influenced conception rates (P=0.02), with animals vaccinated 27 to 29 (52%) days or 30 to 37 (52%) days prebreeding exhibiting decreased conception rates compared to animals vaccinated 46 to 89 days prebreeding (P<0.03; 64%). There was no treatment by interval interaction (P=0.79), effect of treatment (P=0.18), or treatment by interval interaction (P=0.17) on breeding season pregnancy rates. In summary, vaccination of previously vaccinated beef cows and heifers with a MLV vaccine pre-breeding (27 to 89 d) was associated with decreased AI conception rates compared to a CA/IV vaccine.