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Photosensitisation is a very painful skin condition

Photosensitisation is a very painful skin condition in cattle. More commonly seen in sunny weather. Primary photosensitisation is caused by cattle eating plants that contain photodynamic agents such as St John’s Wort or Giant Hogweed. Secondary photosensitisation is a result of liver damage such as from liver fluke or poisoning. The damaged liver does not effectively remove the photodynamic agents from the blood. 

These photodynamic agents in the bloodstream cause an inflammatory response when exposed to sunlight that damages the skin cells. 

It is a very painful disease. Animals are restless and uncomfortable. Typically, non-pigmented skin is more severely affected. The animal’s muzzle is often red and ulcerated, white areas of skin are swollen. The udder or scrotum becomes red and inflamed. The skin initially is hot, painful to touch and may ooze a clear yellow fluid before the skin eventually dries out and sloughs off. Large areas of skin can be lost, which is not only painful, but can lead to secondary bacterial infections. 

Affected animals need to be housed in a dark environment away from direct sunlight. Anti-inflammatories are essential and often antibiotics are used to help with secondary skin infections. Animals can recover but remain sensitive to sunlight.