Lin Dong

Bovine leukemia virus (BLV) is widespread globally and causes economic losses in the cattle industry. Shandong Province plays a significant role in China's livestock industry, with an increasing importance in food of Holstein and Angus cattle. However, BLV prevalence in Holstein and Angus breeds in Shandong Province remains unclear. In particular, there are no reports of BLV prevalence of Angus cattle in field surveys worldwide. In this study, 613 samples from six large‐scale farms (> 1000 heads per farm) in Binzhou and Weifang cities were screened for BLV antibodies (gp51) using an enzyme‐linked immunosorbent assay. The samples included 303 Angus (beef) and 310 Holstein (dairy) cattle. All Angus breeding samples from the three farms were BLV‐negative at both the animal‐ and herd‐level prevalences. In contrast, 62 of 310 Holstein cattle (20.0%) from three dairy farms were positive for BLV antibodies. For example, 35/110 (31.8%), 19/100 (19.0%), and 8/100 (8.0%) samples from the D, E, and F farms, respectively, were BLV‐positive. Notably, the animal‐ and herd‐level prevalences for Holstein cattle exhibited 20% and 100% positivity, respectively. These findings offer significant insights into the BLV status of Holstein and Angus cattle in Shandong Province, China.

Bovine leukemia virus (BLV), the most prevalent neoplastic disease of cattle worldwide, is the causative agent of enzootic bovine leukosis. Polymorphisms in the bovine leukocyte antigen (BoLA)-DRB3 gene can influence host immune responses to pathogens, including BLV. However, the associations between specific BoLA-DRB3 alleles, BLV proviral load (PVL), a useful index for estimating disease progression and transmission risk, and BLV infection in Chinese cattle remain unknown. In this study, we identified 28 previously reported alleles in 289 Holstein cattle from Shandong Province, China, using polymerase chain reaction sequence-based typing. We further investigated whether BoLA-DRB3 polymorphisms influenced infection status and identified BoLA-DRB3*011:01 as an allele associated with susceptibility to BLV infection. An association analysis of allele frequencies between cattle with high and low PVL demonstrated that BoLA-DRB3*014:01:01 was significantly associated with low PVL. Farms with a higher frequency of cattle carrying BoLA-DRB3*014:01:01 had lower mean PVL values than farms with a lower frequency, indicating that resistant alleles are linked to low PVL levels. To our knowledge, this is the first study to demonstrate that BoLA-DRB3 polymorphisms associate with differential susceptibility to BLV infection and PVL in Holstein cattle in China. These findings may contribute to BLV control and eradication efforts through genetic selection.