White muscle disease is a myodegenerative disease that can affect the cardiac and skeletal muscles of primarily foals and on occasion adult horses. It is caused by lack of selenium and vitamin E in the diet, often associated with living in a selenium deficient area, high unsaturated fat intake or unaccustomed exercise.
Selenium deficiency associations with gender, breed, serum vitamin E and creatine kinase, clinical signs and diagnoses in horses of different age groups: A retrospective examination 1996–2011 Equine Veterinary Journal. 2012