Enzootic bovine leukosis (EBL) caused by bovine leukosis virus (BLV) is a widespread infection of dairy cattle that causes lymphoma in a minority of infected animals, with significant welfare implications for affected individuals.
Cattle that progress to lymphoma experience a prolonged deterioration — growing internal tumours compress organs, cause difficulty swallowing, and lead to progressive weight loss and weakness. The timeline from infection to lymphoma development means affected cows may suffer for months before their condition is recognised as terminal. Because most infected cattle show no signs, widespread subclinical infection passes unnoticed. The welfare concern is focused on the minority that develop lymphoma — ensuring these animals are identified and euthanised humanely rather than maintained through a slow decline. Eradication programmes that reduce herd prevalence protect future generations of cattle from both the disease and the welfare consequences of lymphoma.