Adequate Selenium Intake Guards Against White Muscle Disease in Horses

In areas of the world where selenium levels in the soil and forages are inadequate, selenium supplementation is necessary to prevent the appearance of selenium deficiency. The most common manner in which selenium supplementation is achieved is by adding sodium selenite to the grain mix. Most well-formulated equine diets contain a level that is adequate to meet the horse’s nutritional requirement for selenium when fed at recommended amounts.

Selenium deficiency is characterized by white muscle disease in foals. The skeletal muscle is pale to white in color due to degeneration of the muscle cells. The cardiac muscle is also affected. Foals exhibiting white muscle disease are frequently weak at birth, suffer from respiratory distress, and have difficulty nursing. Due to the loss of muscle integrity, respiration is impaired and foals often die of respiratory failure.

The serum selenium level and plasma glutathione peroxidase (a selenium dependent enzyme) concentration of mares has been effectively used as a predictive diagnostic tool in averting the incidence of white muscle disease in foals produced by mares grazing selenium-deficient pastures. The expected normal range of serum selenium in selenium adequate mares is from 0.06 to 0.15 ppm (mg/100 ml), although mares at the lower end of the expected range have been known to produce foals with white muscle disease. Plasma glutathione peroxidase concentrations of less than 20 units are indicative of marginal selenium status and horses with this low value should be treated by either addition of dietary selenium or by injection of selenium. It is worth noting that selenium injections have resulted in anaphylactic shock on occasion, and as such should be administered with care.