Reevaluating the economic impact of bovine leukemia virus in beef production: No association between infection and carcass weight in Japanese Black cattle.

Bovine leukemia virus (BLV) is a retrovirus that infects bovine B lymphocytes and causes enzootic bovine leukosis in approximately 1-5% of infected cattle. Although recent studies have shown that older Holstein cattle with a high proviral load (PVL) exhibit significantly reduced carcass weight, the impact of BLV infection on young fattening cattle remains unclear. In this study, we investigated the relationship between BLV infection and carcass weight in fattening Japanese Black cattle, a breed of high economic importance in beef production, worldwide. A total of 474 blood samples were collected from slaughterhouses in Kyushu, Japan. Cattle were classified into enzyme-linked immunosorbent assay (ELISA)-negative and ELISA-positive groups to assess the effect of BLV infection, and PVL was quantified. No significant differences in carcass weight were observed between ELISA groups, and no significant correlation was found between carcass weight and PVL. These findings suggest that subclinical BLV infection does not directly affect carcass weight in fattening Japanese Black cattle. Although BLV may not cause immediate economic losses in beef production, potential long-term effects and breed-specific responses warrant further investigation. To minimize economic losses while maintaining practical disease control, strategic herd management approaches are essential. We propose that BLV-infected cattle, particularly high-risk animals with elevated PVL, be separated from uninfected cattle during fattening and subsequently shipped for processing. This strategy may offer a realistic, economically viable, and low-burden approach to controlling BLV transmission in beef herds.