Nutritional muscular dystrophy (white muscle disease) is a degeneration of the skeletal and cardiac muscles of lambs. White muscle disease is most commonly found among lambs grazing irrigated pastures. The incidence is generally higher for lambs on legume pasture, creep feed, or other high-quality diets. Generally, ewes being fed high levels of alfalfa hay are most likely to have lambs suffering from white muscle disease.

The condition is related to deficiencies in selenium or vitamin E. Selenium deficiency can interfere with the transport of vitamin E.

White muscle disease may be present at birth. Affected lambs may die from starvation or exposure, and they are more susceptible to scours and acute pneumonia. The disease is more common in lambs 3 to 8 weeks of age, but it also occurs in older lambs.

The disease affects skeletal muscles, causing symptoms of progressive paralysis. Typically, the back is arched such that affected lambs cannot move properly, particularly off the hind legs. They have an open-shouldered appearance because the muscles of the shoulder girdle relax, and the forelegs may be spread excessively. Muscles of the heart, diaphragm, tongue, and esophagus are also commonly affected. Some lambs die suddenly from heart failure without prior clinical symptoms. This occurrence is usually stimulated by an increase of physical activity. More often, a slow progressive cardiac failure results. This leads to passive lung anemia and slow death from suffocation. If passive lung anemia occurs, the disorder can be confused with pneumonia.

The condition can be effectively prevented and treated with injections of selenium and vitamin E. Where white muscle disease is an annual problem, best results are obtained by giving ewes a selenium injection one to four weeks before lambing. If white muscle disease is diagnosed in a flock, all lambs should be treated at birth. Affected lambs respond positively to injections of selenium, or selenium and vitamin E. Including grain sorghum, wheat, and linseed meal in the ration of pregnant ewes and linseed meal in creep rations can reduce the incidence of this disease.