Bovine Photosensitization: Welfare and Management

Key Facts

• Primary photosensitization occurs when photodynamic agents from plants (St. John's Wort, buckwheat) accumulate in skin
• Hepatogenous photosensitization is more common and more serious — liver damage prevents excretion of phylloerythrin
• Clinical signs include severe skin lesions on white areas, head-shaking, skin sloughing, and intense agitation
• Affected cattle desperately seek shade — uncontrolled exposure causes progressive deterioration
• Treatment involves removing the animal from sunlight immediately and identifying and treating the liver cause

Welfare Considerations

Photosensitization causes some of the most severe acute skin welfare suffering in cattle. The pain from affected areas is intense — cattle with hepatogenous photosensitization are genuinely agonized, scratching, rubbing, head-shaking, and desperately seeking shade. Skin can slough from severely affected areas, creating open wounds. The welfare imperative is immediate provision of shade and removal from further UV exposure. NSAIDs provide pain relief while the underlying cause is investigated. Hepatogenous cases require prompt liver assessment as the underlying liver pathology may itself be life-threatening.

What You Can Do

• Provide immediate shade access for any cattle showing signs of photosensitization
• Administer NSAIDs urgently for pain relief — photosensitization pain is severe and welfare-impacting
• Identify and remove the source plant or hepatotoxin causing the condition
• Investigate liver function in all cases to differentiate primary from hepatogenous photosensitization
• Keep white-faced or white-sided cattle away from photosensitizing plants as a preventive measure