Why selenium is crucial for your horse's health. Discover how to prevent deficiencies and protect against nutritional muscular dystrophy (NMD) with proper nutrition and essential minerals.
Understanding Nutritional Myodegeneration (White Muscle Disease) in Horses
Nutritional Myodegeneration (NMD), commonly known as "white muscle disease," is a serious disorder characterized by the degeneration of skeletal and cardiac muscles. This condition is primarily caused by a deficiency in selenium and Vitamin E, two critical antioxidant nutrients that neutralize free radicals. Without these antioxidants, unstable molecules damage muscle cells, leading to premature cell death and giving the affected tissue a characteristic white appearance.
While NMD most frequently affects newborn foals; often due to the mare's selenium deficiency during gestation or a lack of Vitamin E in the colostrum, it is not limited to young horses. Adult horses can also develop white muscle disease if their daily dietary intake of selenium is insufficient. Proper supplementation and monitoring are essential to prevent this debilitating muscle condition.
The Importance of Selenium
Selenium is a "micromineral," meaning horses only need it in small amounts to meet their dietary requirements. According to the National Research Council, the selenium requirement for a horse is 0.1 mg/kg of diet (equivalent to ppm), or about 1 mg per day for the average horse.
Despite being needed in small amounts, owners should not underestimate selenium's importance as an antioxidant. Oxidation is a metabolic process that converts fats, proteins, and carbohydrates into carbon dioxide, water, and energy. However, this process can sometimes be harmful, as the free radicals produced during oxidation can damage cells. Antioxidants like selenium and Vitamin E can neutralize free radicals and stop them from causing damage.
Selenium also plays a role in producing specific proteins in the body, such as selenoproteins. Selenoproteins are muscle proteins, and a deficiency is known to cause muscular degeneration. For this reason, selenium and Vitamin E supplementation are often used to prevent muscle disorders like "tying-up."
Symptoms of NMD
Common signs of NMD include:
- Rapid heart rate
- Difficulty standing up
- Tying up
- Difficulty eating
- High respiration rate
- Inadequate suckle reflex
- Jaw clenching
- Muscle fasciculations (tremors)
- Trembling
- Stiffness
- Darker-than-normal urine due to higher nitrogen excretion from muscle tissue breakdown
Besides physical signs, NMD is associated with metabolic abnormalities that can be detected in lab tests, including:
- Increased potassium
- Reduced amounts of sodium, calcium, and chloride
- Increased serum muscle enzymes
- Low to normal serum vitamin E levels
NMD typically occurs in horses living in areas with selenium-deficient soil. This is common in coastal states (Pacific and Atlantic), parts of the Midwest, and Canada. Horses that feed mainly on pasture and hay in these regions have a higher risk of deficiency.
Treatment
Treatment for selenium deficiency can range from selenium injections and Vitamin E supplementation to supportive therapies and antibiotics for horses with secondary infections.
Selenium can be injected intramuscularly, helping levels in whole blood return to normal within 30 days. Oral vitamin E supplements can also be administered, but the supplement should be a natural form of vitamin E, such as d-alpha-tocopherol acetate.
Foals require supportive care since they are often uncoordinated, weak, and have difficulty swallowing. They will likely need help standing up and nursing. In some cases, your veterinarian might refer your foal to a clinic where it can be fed through a nasogastric tube. Antibiotics might also be administered to foals that have developed respiratory issues due to NMD.
The mortality rate for NMD is about 30–45%. For foals, the condition may be reversible if caught and treated early. Unfortunately, adult horses with NMD have a poor prognosis.
Prevention
NMD is easily avoidable if you employ the following management strategies:
- Ensure the diet provides balanced levels of vitamins and minerals. Talk with your veterinarian about the best selenium and vitamin E supplement to add to your horse's diet.
- For broodmares, ensure their diet contains adequate levels of selenium and vitamin E. You should also monitor their antioxidant levels.
- If you grow your own forage, monitor the selenium content of the soil. Test your soil every year by submitting a sample to your county’s extension office.
- Have your hay analyzed to determine its selenium content.
Conclusion
Never underestimate the importance of a micromineral like selenium in your horse’s diet. Even being slightly under the recommended amount can eventually lead to NMD, which can be fatal if unrecognized or untreated. While NMD is more common in foals, it can still affect adult horses.
