Detection of Antibodies Against Bovine Herpes Virus 1, Bovine Viral Diarrhea Virus and Bovine Respiratory Syncytial Virus in Early and Ultra-Early Weaned Beef Calves

Bovine respiratory disease is the leading cause of morbidity and mortality in weaned calves. In Argentina, two weaning practices have been implemented. In the early weaning, the calf is removed from the cow at 60-70 days of age while in ultra-early weaning the calf is weaned at 30-45 days of age. The purposes of both systems is to improve cow body condition, calf performance, conception rates and forage availability for the cow. In this study we evaluated the antibody response against BVDV and BoHV1 in early and ultra-early weaned calves that had received a conventional vaccination schedule (first dose at weaning and a booster 21 days post-weaning). Passively acquired immunity may provide protection against disease caused by these viruses. The presence of antibodies against BRSV, a virus that was not present in the vaccines used, was also evaluated as an indirect indicator of viral circulation in the herd. At the time of vaccination, calves presented a wide range of maternallyderived antibody titers. Vaccination against BoHV-1 did not evoke seroconvertion and antibody titers continued to decay throughout the experience. After vaccination, seroconversion to BVDV could be detected in calves with low antibody titers, while higher antibody titers exerted an inhibitory effect of the active humoral response.