White Muscle Disease
(Nutritional Myodegeneration)

Causes: Muscle problems associated with this disease are caused by low dietary levels of selenium and vitamin E. Certain areas of the United States are considered adequate, high, or low in selenium levels. Therefore, depending on the geographical location where the animals reside, certain horses are at a greater risk of developing white muscle disease. This disease is found mostly in young, fast growing horses, cattle, or sheep, and is mostly due to low levels of selenium in the motherís body during gestation.

Clinical Signs: It is important to realize that this disease can cause problems in the heart and not just in the skeletal muscles of the body. When the heart is affected, the animal shows signs similar to pneumonia. These include difficulty breathing, a frothy nasal discharge (may be blood stained), and a fever. The heart and respiratory rates are elevated and often irregular.

When the muscles of the body are affected, the animal may be weak or stiff, depending on the stage of the disease. At first, the animal is usually weak and unable to rise. With time, the animal may become stiff, with the legs swollen and painful.

Diagnosis: An assumptive diagnosis can be made, based on physical exam and past history. This is supported by measuring selenium and CPK levels in the blood. A diseased animal will have selenium levels less than 0.04 parts per million (ppm), and CPK levels in the thousands. Both forms of this disease can be diagnosed at necropsy.

Treatment: With the problems that involve the heart, all treatments are usually ineffective. For treating the muscle form of the disease, supplemental selenium and vitamin E are required. Most selenium products come combined with vitamin E; however, the levels of vitamin E in these products are usually too low. It is often necessary to give additional vitamin E. Pay particular attention to the concentrations of selenium per mL, as they vary greatly in each product. Also, keep in mind that excessive levels of selenium will result in selenium toxicity.

Prevention: Supplemental sources of selenium can be provided in an oral or injectable form. Selenium can be fed at 1 mg/head/day. To prevent toxicity, it is recommended that periodic blood testing be performed to monitor and regulate selenium replacement.