Descriptive epidemiology of postnatal bovine viral diarrhea virus infection in intensively managed dairy heifers

Objective-To evaluate risk of bovine viral diarrhea virus (BVDV) infection between birth and 9 months of age for dairy replacement heifers raised unde r typical dry-lot management conditions. Design-Longitudinal observational study. Animals-446 calves. Procedure-Calves were randomly selected from 2 dairies that used killed and modified-live BVDV vaccines. Repeated serologic and BVDV polymerase chain reaction assays were used to estimate risk of BVDV infection in calves of v arious ages (1 to 60 days; 61 to 100 days; 101 days to 9 months) and to est imate overall infection rate by 9 months of age. Results-Risk of BVDV infection increased with age (maximum risk, 150 to 260 days). Proportion of calves infected with BVDV by 9 months of age was high er for dairy A (0.665), compared with dairy B (0.357). Percentage infected with BVDV type I did not differ between dairy A (18.2%) and dairy B (15.2%) , whereas percentage infected with BVDV type II for dairy A (50%) was twice that for dairy B (21%). Between 210 and 220 days of age, infection with BV DV regardless of type was >1.3%/d on dairy A and 0.5%/d on dairy B. Conclusions and Clinical Relevance-Under dry-lot conditions, a considerable amount of BVDV infection may occur before 9 months of age. Risk of infecti on increases with age. Although dairies may appear to have similar manageme nt practices, there can be considerably different risks of BVDV infection a mong dairies.