Ovine pulmonary adenocarcinoma (OPA) is a contagious lung cancer caused by Jaagsiekte sheep retrovirus, causing progressive respiratory failure with significant welfare impact in affected flocks.
OPA causes a slow, progressive decline in respiratory function that significantly compromises welfare. Affected sheep experience increasing difficulty breathing, inability to keep up with the flock, and eventual exhaustion. The chronic nature of the disease means animals may suffer for months before being identified and humanely euthanized. Early detection through regular flock monitoring — listening for respiratory changes, observing body condition, and performing the "wheelbarrow test" — is critical to minimizing suffering. Biosecurity measures to prevent introduction of JSRV into naive flocks are the primary welfare intervention.