A study highlights the severe impact of bovine leukemia virus (BLV) on U.S. and Canadian dairy herds, showing its role in reducing milk production, increasing mastitis, metritis, and culling risks, while causing significant economic losses.
A new study highlights the association between bovine leukemia virus (BLV) infections and various detrimental dairy diseases, impacting herds across the United States and Canada. BLV, which causes enzootic bovine leukosis—a retroviral disease of the lymphoid tissue—has been shown to have far-reaching economic and health impacts. According to a report by the United States Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS), this disease not only reduces milk production but also increases risks of mastitis, metritis, and premature culling.
Recent USDA-APHIS findings indicate that BLV is widespread, with 89% of U.S. dairy herds testing positive for BLV-infected cattle. Similarly, data from Canada report that 91% of dairy herds are BLV-positive, signaling a near-ubiquitous prevalence in North America’s dairy industry. In 2003, BLV-related economic losses in the U.S. were estimated at $525 million annually, largely due to decreased milk production. Adjusted for inflation, these losses are now projected to total around $900 million per year.
Health and Economic Impact of BLV
Studies led by veterinary and agricultural researchers across North America have established connections between BLV and several other dairy diseases. Infected cattle experience weakened immune responses, making them more susceptible to infections like mastitis and metritis. Recent research by Hernandez et al. (2024) shows that BLV-positive heifers have a 1.31 times higher risk of developing metritis in their first lactation compared to non-infected animals, with BLV-positive cows also facing a 1.33 times higher risk of early culling. Subclinical mastitis was shown to be more common in cattle with high-proviral loads of BLV, where infected cows had 2.61 times the odds of developing the condition than non-infected cows.
BLV is known to impair the immune system, with high viral loads inducing inflammatory responses that lead to tissue damage. These immune challenges further compromise cattle health, increasing the risk of severe infections and highlighting the virus’s impact on dairy productivity and sustainability.
Risk Factors for BLV Infection
Several risk factors contribute to BLV’s spread within herds. A study by Hutchinson et al. (2020) found that milking frequency, needle reuse, bedding types, and herd size all play a role in increasing BLV prevalence. Other reports indicate that BLV infection disrupts innate and adaptive immune responses, as infected cells exhibit altered gene expression related to viral defense. Studies also link high BLV viral loads with exaggerated inflammatory responses, suggesting that dairy producers should be vigilant in controlling infection within herds.
As dairy farmers contend with BLV’s broad impacts, researchers are urging greater attention to herd management practices that could mitigate infection risks, such as optimizing hygiene protocols and reducing herd sizes where possible.
