BOLA‐DRB3 gene polymorphisms influence bovine leukaemia virus infection levels in Holstein and Holstein × Jersey crossbreed dairy cattle

Summary Bovine leukemia virus (BLV) infections, causing persistent lymphocytosis and lethal lymphosarcoma in cattle, have reached high endemicity on dairy farms. We observed extensive inter‐individual variation in the level of infection (LI) by assessing differences in proviral load in peripheral blood. This phenotypic variation appears to be determined by host genetics variants, especially those located in the BoLA‐DRB3 MHCII molecule. We performed an association study using sequencing‐based typed BOLA‐DRB3 alleles from over 800 Holstein and Holstein × Jersey cows considering LI in vivo and accounting for filial relationships. The DBR3*0902 allele was associated with a low level of infection (LLI) (