Cattle infected with bovine leukemia virus (BLV) have disrupted immune systems, associated with reduced milk production, shortened lifespan, and predisposition to lymphoma. The objective of this intervention study was to develop an integrated method to reduce BLV prevalence within a large commercial dairy herd. Blood samples were collected from milking cows to determine lymphocyte count, antibodies against BLV, and proviral load (PVL) using complete blood cell counts, enzyme-linked immunosorbent assay, and quantitative polymerase chain reaction methods, respectively. Anticoagulated whole blood samples were collected to measure LC and harvest plasma for antibody detection. The PVL was quantified from cows with positive antibody results. Test results were used to inform herd management decisions targeting those cows most likely to transmit BLV or develop disease by reducing contact with herdmates and culling. The risk value for lymphocytosis (P<0.001) and the mean PVL (P<0.001) was significantly reduced during the four quarters of intervention. Additionally, it was found that PVL was associated with clinical lameness (P<0.001) but not with clinical mastitis (P=0.557), and there was no association found between LC and clinical lameness (P=0.074) or clinical mastitis (P=0.966). This novel, multifaceted pilot study effectively reduced BLV prevalence within the herd.
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