Bit & Bridle

Equine Vitamin E Deficiency

Other Names

  • Equine Neuroaxonal Dystrophy (eNAD)
  • Equine Degenerative Myeloencephalopathy (EDM)
  • Equine Motor Neuron Disease (EMND)
  • Vitamin E-Deficient Myopathy (VEM)
  • Nutritional Muscular Dystrophy

What Is Equine Vitamin E Deficiency?

Vitamin E is a fat-soluble antioxidant that plays a critical role in maintaining healthy muscle tissue, neurological function, and immune competence in horses. Unlike many nutrients, horses cannot synthesise vitamin E endogenously — they must obtain it entirely from their diet. When dietary intake falls short of daily requirements, a range of debilitating conditions can develop, from subtle gait abnormalities to severe neurological disease.

Fresh, green pasture grass is by far the richest natural source of vitamin E for horses. The problem arises when horses are kept on dry lots, fed predominantly hay, or subsist on poor-quality pasture during winter months. Hay loses the majority of its vitamin E content within weeks of cutting, meaning horses consuming hay as their primary forage may be chronically deficient even when rations appear adequate on paper.

The National Research Council recommends a baseline of 1–2 IU of vitamin E per kilogram of body weight per day for a horse at maintenance. Working horses, breeding stock, and growing youngsters have considerably higher requirements. Horses in heavy work, pregnant and lactating mares, and those recovering from illness may need 3–10 times the maintenance dose depending on individual circumstances.

Causes

The primary cause of vitamin E deficiency is straightforward: insufficient intake relative to demand. However, several compounding factors influence how quickly a horse becomes deficient and how severe the clinical consequences are:

  • Dietary insufficiency: Hay-based diets, particularly hay stored for more than two to three months, supply very little bioavailable vitamin E. Horses without access to fresh pasture are particularly vulnerable.
  • Increased physiological demand: Performance horses, breeding mares, foals, and geriatric horses all have elevated requirements that hay alone cannot meet.
  • Malabsorption: Horses with inflammatory bowel disease, chronic diarrhoea, or other gastrointestinal conditions may absorb fat-soluble vitamins poorly, even when dietary intake appears adequate.
  • High selenium intake: Selenium and vitamin E share interrelated functions in antioxidant pathways. Diets high in selenium may alter vitamin E metabolism, and vice versa.
  • Feed storage: Heat, light, and oxidation degrade vitamin E in commercially prepared feeds and supplements. Improperly stored feed or supplements past their use-by date contribute to shortfalls.
  • Genetic susceptibility: Some individual horses, and potentially some breeds, appear genetically predisposed to developing neurological forms of the disease (eNAD/EDM) even when dietary intake seems borderline adequate.

Symptoms and Signs

The clinical presentation of vitamin E deficiency varies considerably depending on which body systems are most affected, the duration of the deficiency, and the individual horse’s age and susceptibility. The three major syndromes are:

Equine Motor Neuron Disease (EMND)

EMND is seen in adult horses, typically those with prolonged exposure to pastures without green grass. Clinical signs include progressive muscle wasting, particularly of the topline and hindquarters, an unusual stance with all four limbs drawn together beneath the body, excessive sweating, low head carriage, and a characteristic shifting of weight from limb to limb at rest. Affected horses often eat well but lose condition despite good appetite. Some develop retinal pigment changes visible on ophthalmic examination.

Equine Neuroaxonal Dystrophy and Equine Degenerative Myeloencephalopathy (eNAD/EDM)

These closely related neurological conditions typically present in young horses (under three years of age) and are characterised by symmetric ataxia (incoordination), weakness, and altered proprioception. Affected foals and young horses stumble, have difficulty backing up, and may show hypermetria (exaggerated limb movement). The condition is degenerative, meaning clinical signs typically worsen over time without treatment.

Nutritional Myopathy (White Muscle Disease / Vitamin E-Deficient Myopathy)

Muscular forms of the disease cause stiffness, reluctance to move, muscle pain on palpation, and elevations in muscle enzymes such as creatine kinase (CK) and aspartate aminotransferase (AST). Severely affected foals may be unable to stand or nurse. In adults, the clinical picture can mimic exertional rhabdomyolysis (tying-up), particularly following exercise.

Diagnosis

Diagnosis is based on a combination of clinical signs, dietary history, and laboratory findings:

  • Serum alpha-tocopherol (vitamin E) levels: Normal values in horses are typically 2–4 micrograms per millilitre. Levels below 1.5 µg/mL suggest deficiency; levels below 1.0 µg/mL are consistent with clinical disease.
  • Selenium status: Selenium and vitamin E are metabolically linked; selenium should be measured concurrently as combined deficiency is common.
  • Muscle enzyme panel: Elevated CK and AST support muscular involvement.
  • Cerebrospinal fluid (CSF) analysis: May reveal elevated protein in cases with significant neurological involvement.
  • Ophthalmoscopic examination: Characteristic retinal pigment changes can support a diagnosis of EMND.
  • Biopsy: In advanced or uncertain cases, skeletal muscle or spinal cord biopsy may be performed post-mortem or, occasionally, ante-mortem to confirm the diagnosis.

Treatment

Treatment centres on aggressive supplementation to restore normal serum vitamin E levels as quickly as possible, combined with addressing any underlying dietary deficiencies:

  • Oral supplementation: Natural-source vitamin E (d-alpha-tocopherol) is more bioavailable than synthetic forms (dl-alpha-tocopherol). Therapeutic doses typically range from 5,000–10,000 IU per day for adult horses, depending on severity and veterinary guidance. Water-dispersible or emulsified formulations raise serum levels faster than powdered forms.
  • Access to fresh pasture: Where possible, turnout on good-quality green pasture should be restored as this provides highly bioavailable natural vitamin E.
  • Dietary review: The overall diet should be reviewed by a qualified equine nutritionist. Selenium supplementation may be recommended concurrently but must be approached cautiously due to selenium’s narrow therapeutic margin.
  • Supportive care: Horses with significant muscle pain or neurological signs may benefit from anti-inflammatory medication, rest, and nursing care during the acute phase.

Recovery depends on which syndrome is present. EMND horses often show meaningful improvement with supplementation if caught early, though horses with advanced muscle wasting may not fully recover. Horses with eNAD/EDM rarely improve significantly once neurological deficits are established, though supplementation may slow progression. For further guidance on management, the British Equine Veterinary Association (BEVA) maintains resources for horse owners navigating neurological conditions.

Prevention

Prevention is considerably more straightforward than treatment:

  • Ensure regular access to fresh green pasture where possible — even a few hours’ daily grazing can significantly boost vitamin E intake.
  • For horses on hay-based diets, provide a commercial vitamin E supplement throughout winter and whenever pasture access is limited. Choose natural-source (d-alpha-tocopherol) formulations for best bioavailability.
  • Monitor serum vitamin E levels annually in horses at risk — those without pasture access, heavily worked horses, and breeding stock.
  • Store feeds and supplements correctly: cool, dry, and away from direct sunlight. Do not use supplements past their expiry date.
  • Work with an equine nutritionist to audit the diet of young stock, performance horses, and broodmares, as their requirements exceed standard maintenance guidelines.

For more on managing equine nutrition, see our guide to equine forage and how to support horses with Equine Azoturia, another muscular condition linked to metabolic imbalance.

Prognosis

Prognosis is heavily dependent on the form of disease present and the stage at which it is identified. Horses with EMND diagnosed early and treated promptly often show marked clinical improvement within weeks, though some residual muscle atrophy may persist. Horses with advanced or long-standing EMND have a more guarded prognosis and may never return to full athletic function.

Horses with eNAD/EDM carry the most guarded prognosis. Neurological damage in the spinal cord is largely irreversible, and most affected horses will remain ataxic to some degree. With careful management, many can be maintained as pasture companions, but return to ridden work is often not achievable.

Horses with primary nutritional myopathy, particularly foals with white muscle disease, may recover well if treated early and aggressively. Those that develop severe muscle necrosis or myoglobinuria (muscle pigment in the urine) have a more guarded outlook.

When to Call the Vet

Contact your veterinary surgeon promptly if you observe any of the following:

  • Unexplained progressive muscle wasting, particularly of the topline and hindquarters
  • Altered gait, stumbling, or loss of coordination in a young horse
  • Stiffness, reluctance to move, or apparent muscle pain, especially in horses on hay-only diets
  • A foal that is weak, unable to stand, or failing to nurse adequately
  • A horse that appears to bear equal weight on all four feet at rest with an unusual hunched posture

Early veterinary assessment and blood testing allow treatment to begin before irreversible damage occurs. This is one condition where prompt action genuinely changes outcomes.

Frequently Asked Questions

How quickly can a horse become vitamin E deficient on a hay-only diet?

Serum vitamin E levels can begin to fall within weeks of removing fresh pasture from the diet, and overt deficiency may develop within two to four months depending on baseline levels, hay quality, and individual metabolism. Horses on hay-based diets without supplementation should be tested annually.

Can I use a general horse vitamin supplement rather than a dedicated vitamin E product?

Many general supplements provide only modest levels of vitamin E, and the synthetic (dl-alpha-tocopherol) form commonly used is less bioavailable than natural-source vitamin E. If deficiency is suspected or confirmed, a dedicated vitamin E supplement using natural d-alpha-tocopherol in a water-dispersible format is considerably more effective than a general multivitamin.

Is vitamin E deficiency linked to tying-up in horses?

Yes. Vitamin E deficiency can contribute to episodes of exertional rhabdomyolysis (tying-up), particularly in horses with underlying muscular susceptibility. However, tying-up has multiple causes, and vitamin E status is just one factor. A full metabolic workup is warranted for horses with recurrent episodes. See our article on Equine Azoturia for more detail.

Are certain breeds more susceptible to eNAD/EDM?

Quarter Horses, Appaloosas, Standardbreds, and Thoroughbreds appear to have higher reported incidence of eNAD/EDM than some other breeds, suggesting a possible genetic component to neurological susceptibility. However, the condition has been documented across many breeds, and dietary management remains the primary modifiable risk factor.