BOLA ‐ DRB 3 gene polymorphisms influence bovine leukaemia virus infection levels in Holstein and Holstein × Jersey crossbreed dairy cattle

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 Bo LA ‐ DRB 3 MHCII molecule. We performed an association study using sequencing‐based typed BOLA ‐ DRB 3 alleles from over 800 Holstein and Holstein × Jersey cows considering LI in vivo and accounting for filial relationships. The DBR 3*0902 allele was associated with a low level of infection ( LLI ) (