Equine Welfare

Horse Photosensitisation: Welfare and Management

Photosensitisation causes painful skin reactions in horses exposed to sunlight, often linked to plant toxins or liver disease, requiring prompt management.

Key Facts

Primary photosensitisation results from ingestion of photodynamic plants such as St John's Wort.
Secondary photosensitisation arises from liver disease impairing phylloerythrin excretion.
White or lightly pigmented skin areas are most severely affected by UV-triggered damage.
Lesions include redness, blistering, cracking, and necrosis of sun-exposed skin.
Severity ranges from mild discomfort to life-threatening skin and liver complications.

Welfare Considerations

Affected horses experience significant pain and distress. Immediate removal from sunlight, identification and elimination of the causative plant or liver trigger, and veterinary treatment are essential. Pain management with NSAIDs, wound care, and provision of shade or stabling during daylight hours are key interventions. Horses with severe cases require intensive nursing. Recovery can take weeks and horses must be protected from sun exposure throughout.

What You Can Do

Learn to identify photosensitising plants in your pasture and remove them promptly.
Provide adequate shade or stable access for horses with white markings during summer.
Seek prompt veterinary attention if skin lesions appear after pasture exposure.
Test liver function when photosensitisation recurs without obvious plant cause.
Consult an equine nutritionist about safe pasture management in affected areas.