Polymorphism of BoLA-DRB3 in Semen and Its Influence on Progeny Derived from Semen with Resistance and Susceptibility to Bovine Leukemia Virus Proviral Load.

Bovine leukemia virus (BLV) is widespread globally and causes economic losses in the cattle industry. BoLA-DRB3 is a polymorphic gene associated with the BLV proviral load (PVL), which correlates with disease progression and transmission risk. However, the distribution of BoLA-DRB3 alleles in semen and their potential impact on the PVL of progeny remain unclear. Here, we investigated whether BLV susceptibility linked to BoLA-DRB3 alleles in semen is inherited by progeny. We analyzed 178 commercial semen samples from Japanese Black sires and identified 20 BoLA-DRB3 alleles and 70 genotypes. The susceptible allele DRB3*016:01 was the most frequent (26.4%), whereas resistant alleles DRB3*011:01 (5.3%) and DRB3*009:02 (0.6%) were rare. Subsequently, we collected blood samples from 200 progeny produced by artificial insemination using 36 of the 178 semen samples. Progeny derived from semen carrying at least one susceptible allele and no resistant alleles had significantly higher PVL in the blood than those derived from semen containing at least one resistant allele. These findings demonstrate that BLV susceptibility is inherited via BoLA-DRB3 alleles in semen and highlight the potential of BoLA-DRB3 alleles as valuable markers in breeding strategies aimed at mitigating BLV infection and transmission.