What are the symptoms of vitamin E and selenium deficiency in horses?

December 22, 2025 •

5 min read

According to extensive veterinary research, deficiencies in the essential antioxidant nutrients vitamin E and selenium are major causes of severe and sometimes irreversible neuromuscular disorders in horses. Recognizing the subtle yet crucial symptoms is the first step toward a correct diagnosis and preventing long-term damage.

Quick Summary

Both vitamin E and selenium deficiencies in horses can lead to muscular and neurological problems, such as white muscle disease in foals, equine motor neuron disease, muscle atrophy, and impaired coordination.

Key Points

Neurological Signs: Chronic vitamin E deficiency can lead to Equine Motor Neuron Disease (EMND), causing progressive muscle atrophy, weight loss, tremors, and a characteristic "elephant on a ball" stance.
Incoordination (Ataxia): Young horses deficient in vitamin E can develop Equine Degenerative Myeloencephalopathy (EDM), resulting in lack of coordination and abnormal posture.
Foal-Specific Dangers: A primary cause of the fatal White Muscle Disease (NMD) in foals is selenium deficiency in the mare, leading to muscle weakness, inability to stand, and difficulty suckling.
Muscle Issues: Both deficiencies can cause muscle weakness, soreness, and poor performance, though selenium deficiency is a more common cause of stiffness and muscular degradation.
Subtle Physical Signs: Look for poor coat or hoof quality (selenium) and a weakened immune system or slow recovery from illness (both vitamin E and selenium) as potential indicators.
Dietary Link: Horses on hay-only diets are at risk for vitamin E deficiency, while those in low-selenium regions are prone to selenium deficiency.

The Critical Role of Vitamin E and Selenium in Equine Health

Vitamin E and selenium are not just beneficial for horses; they are essential for protecting against oxidative stress, a process that can damage cells and lead to disease. As powerful antioxidants, these two nutrients work synergistically to maintain the health of the horse's nervous system, immune response, and muscular function. While most horses get adequate vitamin E from lush, fresh green pasture, levels decline rapidly in hay. Similarly, selenium content in forages depends heavily on regional soil concentrations, with many areas having low soil levels that result in dietary deficiencies. Understanding the specific signs for each deficiency is vital for horse owners and caretakers.

Why Antioxidants Matter

During normal metabolic activity, a horse's body produces free radicals. These unstable molecules can cause cellular damage, particularly in muscle and nerve tissues, if not neutralized by antioxidants. Vitamin E primarily acts in cell membranes, while selenium is integral to the antioxidant enzyme glutathione peroxidase, which protects the cell's watery interior. An insufficient supply of these antioxidants leaves a horse's body vulnerable to damage, which can be accelerated by stressors like intense exercise, illness, or transport.

Distinct Symptoms of Vitamin E Deficiency

Sustained and severe vitamin E deficiency is often linked to neuromuscular diseases and a compromised immune system. The neurological disorders associated with this deficit are particularly concerning.

Neurological Disorders

Equine Motor Neuron Disease (EMND): This condition results from the degeneration of motor neurons in the spinal cord and brainstem. It typically affects older horses with a chronic vitamin E deficiency of 18 months or more. Symptoms include progressive muscle atrophy, particularly in the shoulders and hips, weight loss, a characteristic "elephant on a ball" stance (standing with legs close together), constant weight shifting, and muscle tremors.
Equine Degenerative Myeloencephalopathy (EDM): Found in young, growing horses (6 to 24 months old), EDM is a neurological disorder that affects the spinal cord and brainstem. Symptoms include ataxia (lack of coordination), an abnormal stance, and proprioceptive deficits, which means the horse struggles with perceiving its body's position and movement. Supplementation after clinical signs appear is often ineffective at reversing damage.
Equine Neuroaxonal Dystrophy (eNAD): Closely related to EDM, eNAD is triggered by low dietary vitamin E in genetically susceptible young horses and is characterized by a lack of coordination.

Muscular Atrophy and Weakness

Even without severe neurological disease, vitamin E deficiency can manifest as general muscle weakness, low head carriage, impaired movement, and a diminished immune response, leading to slow recovery from illness.

Distinct Symptoms of Selenium Deficiency

Selenium deficiency most notably affects muscle tissue, particularly in young foals, and can have an impact on fertility and the horse's coat and hoof quality.

White Muscle Disease in Foals

Also known as Nutritional Myodegeneration (NMD), White Muscle Disease is a devastating and often fatal condition primarily affecting newborn foals born to selenium-deficient mares. It is characterized by muscle cell death and the formation of pale scar tissue. Affected foals display severe muscle weakness, an inability to stand or suckle, and rapid or irregular heartbeats. Discolored (red to brown) urine may indicate severe muscle damage.

Adult Horse Symptoms

In adult horses, selenium deficiency can cause:

Muscle stiffness and weakness, especially in the hindquarters.
General poor performance and sluggishness.
Poor coat and hoof quality, and hair loss from the mane and tail in some cases.
A weakened immune system and reduced fertility in broodmares.
Difficulty eating, due to effects on the jaw muscles.

Comparison of Deficiency Symptoms

It is important to understand the overlapping yet distinct symptoms of each deficiency. A combined deficiency can exacerbate issues.


Symptom	Vitamin E Deficiency	Selenium Deficiency
Neurological Issues	Common; major cause of EMND, EDM, and eNAD.	Less common; typically associated with muscular issues, not neurological damage.
Muscle Atrophy	Significant, especially in EMND.	Can cause general muscle degradation and weakness.
Foal Disease	Contributes to white muscle disease, especially via colostrum.	Primary cause of white muscle disease (NMD) in foals.
Performance Issues	Weakness and poor performance.	Sluggishness and reduced athletic performance.
Coat & Hoof	Can cause dry, poor coat quality.	Associated with poor coat, hair loss, and hoof issues.
Immune Response	Compromised and weakened.	Weakened immune system.

Diagnosis, Treatment, and Prevention

How to Test for Deficiencies

To accurately diagnose a deficiency, a veterinarian will need to perform a blood test to measure plasma or serum vitamin E levels and whole blood selenium levels. Regional soil content and a thorough dietary history are also crucial parts of the assessment. In some cases, a muscle biopsy may be necessary to differentiate between different types of myopathies.

Treatment Strategies

Once diagnosed, a horse's diet will need to be changed to increase the intake of the deficient nutrient. For vitamin E deficiency, a natural-source, water-soluble supplement (d-alpha-tocopherol) is often used, as it is more bioavailable. Doses can be high initially, sometimes 5,000-10,000 IU/day for conditions like EMND. For selenium, organic selenium sources, such as selenized yeast, are preferred for better absorption. For foals with white muscle disease, prompt intramuscular injections of selenium are often necessary, alongside supportive care and vitamin E supplementation.

Prevention is Key

The most effective strategy is prevention. Ensure your horse receives adequate fresh, green forage or a balanced supplement if pasture access is limited. Supplementing pregnant mares in deficient areas is critical to prevent white muscle disease in foals. Always consult your veterinarian or an equine nutritionist before starting any new supplement regimen to avoid potential toxicity, as selenium has a narrow safe range. Regular blood tests can help monitor nutrient status, especially in high-risk areas. For more on preventing EMND, visit the Kentucky Equine Research site: Equine Motor Neuron Disease - Kentucky Equine Research.

Conclusion

Vitamin E and selenium deficiencies can lead to a spectrum of health issues in horses, from minor performance declines to life-threatening neuromuscular disorders. Early identification of symptoms such as muscle weakness, poor coordination, or specific neurological signs is critical. Because symptoms can overlap with other conditions, a proper veterinary diagnosis through blood testing is essential. With targeted supplementation and careful dietary management, horse owners can effectively prevent and treat these deficiencies, protecting their horse's long-term health and well-being.

Frequently Asked Questions

The selenium content of pasture and hay depends on the soil in which the plants are grown. Many regions have naturally low soil selenium levels. A forage analysis can determine the specific nutrient content of your hay or grass, and your veterinarian can also test your horse's blood levels.

While severe selenium deficiency is the primary cause of white muscle disease (NMD) in foals, an inadequate supply of vitamin E can also contribute to the condition. Deficiencies in both nutrients are often seen together due to their synergistic antioxidant functions.

Treatment with appropriate supplementation can often halt the progression of deficiency-related issues. However, if neurological damage from conditions like EMND or EDM has occurred, it is often irreversible. Early diagnosis and intervention are critical.

Deficiencies are diagnosed by a veterinarian using blood tests. These tests measure plasma or serum vitamin E levels and whole blood selenium concentrations. A dietary history and physical examination are also important parts of the diagnostic process.

Natural-source vitamin E, specifically d-alpha-tocopherol, is more bioavailable and is often recommended for supplementation. Water-soluble formulations are absorbed more efficiently by the body. Always consult your vet for the correct dosage.

Vitamin E degrades over time after grass is cut and cured into hay. This oxidation process significantly reduces the vitamin's potency, meaning horses on a hay-only diet will likely require supplementation.

Yes, excessive selenium is toxic to horses. The margin of safety is narrow, and over-supplementation can lead to a condition called selenosis, causing hoof abnormalities, lameness, and hair loss. Always test your horse's levels before supplementing and use care to avoid over-dosing.

Yes, certain horses are at higher risk, including those with limited access to fresh green pasture, those in high-stress or heavy work, and horses living in regions with low-selenium soils. Young, growing horses and pregnant or lactating mares have higher needs and are particularly vulnerable.