Response to modified live and killed multivalent viral vaccine in regularly vaccinated, fresh dairy cows.

Vaccination programs for viral pathogens in the dairy industry span the full spectrum of possibilities even though few of these have been evaluated in field situations. One such program is the vaccination of fresh cows 30 to 60 days postpartum with modified live viral (MLV) vaccines. The purpose of this study was to evaluate the antibody response to booster vaccinations during this period. The impact of vaccinations on milk production and reproductive performance was also examined. The response of cattle boosted with MLV bovine viral diarrhea virus (BVDV) was greatly enhanced compared with the saline controls and the killed vaccine test group. Similar increases were not seen with the MLV infectious bovine rhinotracheitis virus (IBR) and bovine respiratory syncytial virus (BRSV). Changes in milk production were not detected. There was a positive effect on the rate of conception with the MLV group even though there was no evidence of the presence of the three viruses in the herd at the time of study. Although this was a single field trial, and thus limited in scope and repeatability, the results indicate that the vaccines used had a positive effect.