Pregnancy outcomes and calf growth in beef cows given modified-live virus vaccination at synchronization for timed artificial insemination

The objective was to compare reproductive outcomes and calf traits after vaccination of suckled beef cows using a commercial modified-live virus (MLV) vaccine that contained bovine herpesvirus 1 and bovine viral diarrhea virus (types 1 and 2) at the initiation of a timed artificial insemination (AI) program. In Experiment 1, cows given MLV vaccine in the previous year were enrolled during the fall 2019 and spring 2020 breeding seasons. At initiation of a 7-day CO-Synch + CIDR synchronization protocol (10 days before breeding), cows were given either MLV vaccine or nothing (CONT). Cows were inseminated 60-66 hours after removal of the CIDR insert and subsequently exposed to bulls starting ~ 1 week after AI. All CONT cows received a killed virus vaccine at mid-pregnancy. For Experiment 2, available cows from fall 2019 were reenrolled and given the same vaccination treatment as in the previous season. Treatment with MLV vaccine did not have effects on AI pregnancy rates (p ≥ 0.31), total season pregnancy rates (p ≥ 0.12), or AI pregnancy losses (p ≥ 0.41). There was also no effect of vaccination treatment on calf birth weight (p ≥ 0.27), weaning weight (p ≥ 0.14), or average daily gain (p ≥ 0.14). In summary, cows given MLV vaccinations on day 10 before breeding experienced no deleterious effects on pregnancy outcomes or calf traits. These findings supported the use of MLV vaccination in previously vaccinated cows at synchronization for timed AI.