Maternal BLV Infection Markers and BoLA-DRB3 Polymorphism Are Associated with BLV Infection Outcomes in Dairy Youngstock

Bovine leukemia virus (BLV) is a deltaretrovirus that establishes lifelong infection in cattle and remains highly prevalent in dairy herds. This study evaluated associations between maternal BLV infection markers, daughter BoLA-DRB3 variation, and BLV outcomes in dairy youngstock. We studied 201 dam–daughter pairs from five dairy farms. BLV status was assessed using ELISA and quantitative PCR (qPCR); maternal qPCR results were available for 126 dams, and daughters were sampled longitudinally during the youngstock period. BoLA-DRB3 genotypes were determined in 199 daughters, and genotype-level epitope breadth was defined as the non-redundant union of predicted BLV Gag epitopes across both alleles. BLV proviral DNA was detected in 33 of 200 daughters (16.5%) in the qPCR outcome used for the main analysis. Among 38 daughters with BLV proviral DNA detected at least once, first detection occurred preweaning in 2, prebreeding in 24, and post-breeding in 12. Maternal ELISA positivity was associated with higher odds of daughter BLV proviral DNA detection (OR 2.74, 95% CI 1.10–6.83), whereas maternal PVL showed a positive but imprecise association (OR 1.94, 95% CI 0.89–4.22). Greater predicted epitope breadth was nominally associated with lower odds of BLV proviral DNA detection (OR 0.76, 95% CI 0.60–0.97; q = 0.162) and BLV seropositivity (OR 0.80, 95% CI 0.65–0.98; q = 0.162), but neither association remained significant after correction for multiple testing. BoLA-DRB3*014:01:01 carriers also had lower observed frequencies of BLV proviral DNA detection and BLV seropositivity. Overall, maternal infection markers were associated with later BLV outcomes in daughters, whereas the BoLA-DRB3 findings provide suggestive evidence of host immunogenetic heterogeneity.