Bovine Viral Diarrhea Virus (BVDV) is a Pestivirus of the Flaviviviridaefamily that infects cattle, and its widespread distribution can cause substantial economic losses worldwide. The aims of this study were: (1) to estimate the prevalence of animals persistently infected (PI) with BVDV in industrial dairy cattle herds in suburb of Mashhad- Iran; and (2) to compare the occurrence of persistently infected (PI) animals in industrial dairy cattle herds where BVDV animals had been either removed from or retained in the herds. In total, 157 blood samples were taken from individual cows from 18 Holstein dairy cattle herds each containing 250-3000 cows in suburb of Mashhad. The blood samples were analyzed for the presence of BVDV using Pestivirus antigen-capture ELISA. Positive animals were retested after three weeks and animals those tested positive again weredefined as PI. We found that only 3/18 herds (16.7%) containedantigen-positive cows, and that only 5/157 animals tested (3.2%) wereantigen positive. All of the positive animals were confirmed as PI, andall of PI cows were less than 17 months old. The true prevalence ofantigen-positive cows was calculated to be 3.31%. A significantproportion (p<0.01) of PI animals exhibited severe weight loss (4/5;80%). and before this study, it was supposed to be sent toslaughterhouse by the farmers due to loss of weight. We conclude that
the prevalence of PI cows in our study is consistent with previousreports. However, our study reveals that severe weight loss in young PIanimals requires their removal to minimize the numbers of BVDVinfectedanimals in the herd.