Infection with bovine leukemia virus belonging to group A or B-1 contributes more strongly to the development of enzootic bovine leukosis in young cattle than the presence of bovine lymphocyte antigen-DRB3 susceptibility alleles.

In this study, we compared the effects of different bovine leukemia virus (BLV) strains and bovine lymphocyte antigen (BoLA)-DRB3 alleles in cattle with enzootic bovine leukosis (EBL) aged either <3 years or ≥3 years. The frequency of infection with BLV belonging to group A or B-1 in cattle aged <3 years with EBL was significantly higher than that in cattle aged ≥3 years, regardless of which BoLA-DRB3 allele was present. This suggests that infection with group A or B-1 BLV contributes more strongly to the development of EBL in young cattle than the presence of early-EBL-onset susceptibility BoLA-DRB3 alleles.