Nutritional Myodegeneration (NMD)

mare and foal

What is nutritional myodegeneration?

Nutritional myodegeneration (NMD), also known as white muscle disease, typically occurs in newborn foals that do not receive enough selenium from their dams. Selenium is an essential trace mineral with important antioxidant functions. Plants take up selenium through the soil and groundwater and are consumed by herbivores in their diets. The amount taken up by most plants varies by geographical area depending on soil conditions. Forage in many parts of the United States (particularly in the Northwest) is actually selenium deficient, which can lead to health issues, especially in foals.

Affected foals often have trouble swallowing appropriately, putting them at risk for developing pneumonia. Severely affected foals have breakdown of their muscles (“tying up”), leading to progressive weakness, organ damage, and sometimes death.

In adult horses, deficiencies of both vitamin E and selenium can occur; however, it is important to assess these nutrients independently.

What are the clinical signs of nutritional myodegeneration?

Clinical signs in foals include rapid, irregular heartbeat, muscle stiffness and trembling, and difficulty getting up. Affected foals can also develop aspiration pneumonia.

How is nutritional myodegeneration diagnosed?

Diagnosis of NMD is based on bloodwork. Enzymes indicative of muscle damage, including serum creatinine kinase (CK) and aspartate transaminase (AST) are increased, whereas whole blood selenium and vitamin E concentrations are low.

How is nutritional myodegeneration treated?

Treatment for affected foals includes intramuscular (IM) injections of selenium and oral supplementation of vitamin E, if vitamin E levels are also low. Supportive therapies including fluids, electrolytes, and antibiotics to treat secondary pneumonia may be used.

Adult horses can also be easily supplemented. The National Research Council (NRC) recommends a minimum of 1 mg (no more than 3 mg) of selenium daily for a 1,100-pound horse. Supplements that include high-selenium yeast are best absorbed by horses, and a variety of supplements are available that provide balanced trace minerals and vitamins.

What is the prognosis for nutritional myodegeneration?

Foals that are treated early have a good prognosis. Foals with cardiac muscle involvement usually do not survive.

How can nutritional myodegeneration be prevented?

Selenium deficiency in foals is easy to prevent through appropriate supplementation of the mare’s diet during pregnancy. It is good practice to know where your forage comes from (Is it from an area with soil known to be deficient in selenium?) and identify other sources of selenium in your horse’s diet (consult the labels for ration balancers and supplements) to make sure they are not under or over supplemented. Work with your veterinarian or equine nutritionist to adjust selenium levels, and discuss specific considerations for pregnant mares.

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