White muscle disease of foals.

White muscle disease (nutritional myodegeneration) of foals is a peracute to subacute myodegenerative disease affecting skeletal and cardiac muscle. It is caused by a dietary deficiency of selenium and vitamin E, usually in association with predisposing factors such as a high intake of dietary unsaturated fats or unaccustomed exercise. White muscle disease has been observed in foals from birth to 1 year of age, particularly those foals born to dams fed selenium-deficient diets, during gestation. The disease in foals may present as an acute, fulminant syndrome, which is rapidly fatal, or a subacute syndrome characterized by profound muscular weakness. Failure of passive transfer, aspiration pneumonia, and stunting are frequent complications. Markedly increased muscle enzyme and low glutathione peroxidase activities are common findings in affected foals. Foals with the subacute form of the disease may survive if they are supplemented early with selenium; however, mortality rates ranging from 30% to 45% have been reported, even for this form of the disease.