Enzootic bovine leukosis (EBL), caused by bovine leukemia virus, is a widespread retroviral infection that causes lymphoma in a proportion of infected cattle — with significant welfare implications for affected individuals.
While most BLV-infected cattle remain clinically normal, the proportion that develop clinical lymphoma experience significant and progressive welfare compromise. Enlarged lymph nodes — particularly in the abdomen and chest — cause organ compression, reduced appetite, and systemic debilitation. Thymic and lymph node enlargement in the chest can impair breathing; abdominal masses can obstruct digestive function, causing bloat and pain. The progressive nature of lymphoma means welfare declines over weeks to months without the possibility of treatment. Early recognition of affected animals and timely humane slaughter or euthanasia is the most welfare-protective management approach. At the herd level, biosecurity measures that reduce virus transmission — dedicated needles for each animal, disinfected equipment, and blood-free obstetrical procedures — reduce the proportion of cattle ever exposed to the welfare risk of lymphoma.