Ovine Pulmonary Adenocarcinoma (OPA) is a contagious lung tumour caused by Jaagsiekte Sheep Retrovirus (JSRV) that represents a significant but underappreciated welfare challenge in sheep flocks worldwide.
OPA represents a welfare challenge characterised by prolonged subclinical suffering - animals develop chronic lung disease over months without obvious clinical signs that trigger intervention. By the time OPA is visually apparent, significant disease is present. The welfare imperative is to develop ante-mortem diagnostic tests that allow early identification and humane culling before advanced disease causes suffering. In the absence of effective treatment or vaccine, flock management focuses on culling clinically suspect animals promptly, avoiding purchase of sheep from high-prevalence flocks, and maintaining good ventilation to reduce transmission. The development of reliable blood tests for early OPA diagnosis would substantially improve welfare management.