Photosensitivity in feedlot calves apparently related to cocoa shells.

Primary photosensitization was observed in 11/78 cross-breed calves. The skin lesions were diffuse dermatitis with thickening and wrinkling with areas of alopecia. The severe photosensitivity dermatitis was associated with cocoa shell ingestion. The lesions resolved after removal of the cocoa shells from the feed ration and prevention of exposure to sunlight. Cocoa shells may contain photodynamic agents that cause photosensitization in calves.