Serological analysis of a small herd sample to predict presence or absence of animals persistently infected with bovine viral diarrhoea virus (BVDV) in dairy herds.

In 10 herds containing animals persistently infected (PI) with bovine viral diarrhoea virus (BVDV) and nine herds without such animals the probabilities of obtaining at least two antibody-positive animals in a test sample of three or five animals selected among animals six to 18 months old were calculated. Among herds with PI animals these probabilities, with the exception of one herd, varied between 0.725 and 0.992 when samples of three animals were tested and between 0.977 and one when samples of five animals were tested. Among herds without PI animals the probabilities varied between 0 and 0.015 when samples of three animals were tested and between 0 and 0.048 when samples of five animals were tested. Thus, based upon a few blood samples, herds with PI animals and herds without PI animals could be distinguished with a high degree of accuracy.