Nutritional Muscular Dystrophy (Nutritional Myopathy or White Muscle Disease) is a disease caused by a deficiency of selenium and vitamin E in dietary intake.[1] Soils that contains low levels of selenium produce forages and grains that are deficient in selenium. Similarly, if the forage is of low quality or is not stored properly it may be deficient in vitamin E.[1] If an animal consumes this type of diet without additional supplementation they become susceptible to this disease.[1] This condition often affects young ruminants, such as calves and lambs.[2]
Selenium and vitamin E are antioxidants therefore, deficiencies of these nutrients leads to oxidative damage to cells within the body. The muscle cells are the most vulnerable to damage in livestock species.
https://en.wikipedia.org/wiki/Nutritional_muscular_dystrophy#:~:text=Nutritional%20Muscular%20Dystrophy%20(Nutritional%20Myopathy,that%20are%20deficient%20in%20selenium.