Herd Health: Modified Live Vaccines at Synchronization

In this episode of Herd Health, the experts review a 2025 study evaluating whether modified live virus (MLV) vaccines can be given at the time of CIDR placement for timed AI in beef cows. In previously vaccinated, multiparous cows about 80 days postpartum, administering an MLV vaccine at synchronization did not negatively affect estrus response, AI pregnancy rates, overall pregnancy rates, pregnancy loss, calving timing, or calf weaning weights. Total pregnancy rates were around 95%, with no significant differences between vaccinated and control groups. The findings suggest that giving an MLV vaccine at synchronization is safe in well-vaccinated adult cows, though results may not apply to naïve heifers.

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