An apparently gluten-induced photosensitivity in horses.

Primary photosensitization was observed in 3 Appaloosa mares. The skin lesions were diffuse erythema followed by edema and subsequently weeping and finally dry gangrene and ulceration. The severe photosensitivity dermatitis was apparently induced by gluten ingestion. Resolution of lesions occurred after withdrawal of the suspected dairy concentrate feed and prevention of exposure to sunlight. Neither the ponies nor donkey, which were not fed with the suspected concentrate, exhibited similar skin lesions or other clinical abnormalities. Gluten metabolites may contain photodynamic agents that cause photosensitization in horses.