Effect of calfhood vaccination on transmission of bovine viral diarrhea virus under typical drylot dairy conditions

Objective-To estimate transmission of bovine viral diarrhea virus (BVDV) an d crude morbidity and mortality ratios in BVDV-vaccinated and unvaccinated dairy heifer calves managed under typical dairy drylot conditions. Design-Randomized clinical trial. Animals-106 female Holstein calves. Procedure Seroconversion rates for BVDV types I and II and proportional mor bidity and mortality ratios were compared between calves given a killed BVD V type-I vaccine at 15 days of age and a modified-live BVDV type-I vaccine at 40 to 45 days of age (n = 53) and calves given no BVDV vaccines (53). Se ra were collected at 45-day intervals as calves moved from individual hutch es to corrals holding increasingly larger numbers of calves. Seroconversion was used as evidence of exposure to BVDV. Results-Crude proportional morbidity (0.16) and mortality (0.17) ratios for control calves did not differ significantly from those of vaccinated calve s (0.28 and 0.12, respectively). The proportion of control calves that sero converted to BVDV type I through 9 months of age (0.629) was significantly higher than that of vaccinated calves that seroconverted, unrelated to vacc ination, during the same period (0.536). Estimated overall protective effec t of vaccination against BVDV type I through 4 to 9 months of age was 48%. The proportion of control calves that seroconverted to BVDV type II (0.356) was not different from that of vaccinated calves (0.470). Conclusions and Clinical Relevance-Findings suggest that calfhood vaccinati on may be an appropriate strategy to help reduce short-term transmission of some but not necessarily all strains of BVDV.