LAUSR

Simple Summary Genetic selection and breeding of bovine leukemia virus (BLV)- susceptible and -resistant cattle based on polymorphisms within the bovine major histocompatibility complex (MHC), namely, bovine leukocyte antigen (BoLA)-DRB3, is important to control horizontal and vertical transmission of BLV. However, its effect on dairy cattle productivity is unknown. Here, we evaluated the effects of BLV infection and BoLA-DRB3 on production performances such as milk yield. BLV infection significantly affected milk yield; however, BoLA-DRB3 had no effect on dairy cattle productivity, suggesting that BLV infection affects dairy productivity more than genetic selective breeding. Our results indicate that genetic selective breeding of resistant cattle, or the preferential culling of susceptible dams, is a promising approach to developing an effective BLV eradication program. Abstract Enzootic bovine leukosis caused by the bovine leukemia virus (BLV) results in substantial damage to the livestock industry; however, we lack an effective cure or vaccine. BoLA-DRB3 polymorphism in BLV-infected cattle is associated with the proviral load (PVL), infectivity in the blood, development of lymphoma, and in utero infection of calves. Additionally, it is related to the PVL, infectivity, and anti-BLV antibody levels in milk. However, the effects of the BoLA-DRB3 allele and BLV infection on dairy cattle productivity remain poorly understood. Therefore, we investigated the effect of BLV infection and BoLA-DRB3 allele polymorphism on dairy cattle productivity in 147 Holstein dams raised on Japanese dairy farms. Our findings suggested that BLV infection significantly increased milk yield. Furthermore, the BoLA-DRB3 allele alone, and the combined effect of BLV infection and the BoLA-DRB3 allele had no effect. These results indicate that on-farm breeding and selection of resistant cattle, or the preferential elimination of susceptible cattle, does not affect dairy cattle productivity. Additionally, BLV infection is more likely to affect dairy cattle productivity than BoLA-DRB3 polymorphism.