Application of antibody titers against bovine viral diarrhea virus (BVDV) as a measure to detect herds with cattle persistently infected with BVDV.

Based on the distribution of antibody titers against bovine viral diarrhea virus (BVDV) in 10 Michigan dairy herds, it was calculated that screening of 5 young stock for BVDV antibody titer could be used to distinguish herds with persistently infected (PI) animals from herds without such animals. The herds were selected to represent 3 different herd categories: A, herds without use of vaccination and without PI animals (5 herds); B, herds with use of killed vaccine but no PI animals (2 herds); C, herds with use of killed vaccine and presence of PI animals (3 herds). The animals were described as having high antibody titers (> or = 128) or low antibody titers (< or = 64). For animals from 9 to 18 months of age, the probability of obtaining at least 3 animals with high titers among a screening sample of 5 animals was calculated as < 0.001 for all herds in category A, < 0.01 for the 2 herds in category B, and > 0.99 for all herds in category C. Thus, among herds in this study, by categorizing 9-18-month-old animals as having high titers (> or = 128) or low titers (< or = 64), herds with PI cattle could be distinguished from other herds by testing only 5 animals.