While some horses receive adequate levels through fresh forage, others may require supplementation to meet their needs. Understanding vitamin E’s importance, sources, and proper supplementation can help ensure your horse is functioning at his best.

What is Vitamin E?

As many horse owners know, the world of supplementation is vast and overwhelming.

The choices are endless; how do we know which supplements our horses truly need? Vitamin E is a fat-soluble antioxidant that plays multiple roles in equine health, making it a key piece in the equine diet.

Its primary functions include:

◆ Muscle Maintenance and Function

Horses rely on strong, healthy muscles for movement, whether they are backyard pets or performance athletes. Vitamin E aids in muscle cell repair and reduces oxidative stress, which occurs during exercise. It helps prevent muscle fatigue and soreness, supporting overall mobility and endurance.

◆ Boosting the Immune System

A strong immune system is essential for keeping horses healthy and resilient against infection. Vitamin E enhances immune responses by supporting white blood cell function and aiding in the production of antibodies.

This is especially vital for foals, senior horses, and those exposed to frequent travel and competition stress.

◆ A Powerful Antioxidant

Oxidative stress damages cells and leads to inflammation. As a potent antioxidant, vitamin E neutralizes free radicals and protects muscles, nerves, and cells from damage. This function is crucial in preventing conditions like equine motor neuron disease (EMND) and exertional rhabdomyolysis (tying-up syndrome).

Best Sources of Vitamin E for Horses

Vitamin E must be obtained through diet, as horses cannot produce it naturally. There are several sources, but the most natural and bioavailable is green grass.

The simplest source of vitamin E is fresh green grass, but many horses aren’t able to graze at least 12 hours per day for six months a year. Photo by Margaret Burlingham/Adobe Stock

However, for horses to obtain sufficient levels of vitamin E for the year through grazing, this requires being turned out on pasture for approximately 12 hours a day, for at least six months out of the year. In many parts of our country, this isn’t a viable option.

Melissa Fenn, DVM, Dipl. ACVIM, and Internal Medicine Specialist at Littleton Equine Medical Center in Colorado weighs in on the alternatives.

“It’s important to consider that commercial feeds, especially those designed for performance horses, often contain vitamin E,” she says. “But these are synthetic formulas, and don’t appear to contribute to their overall vitamin E intake. While hay provides many essential nutrients, the vitamin E content declines significantly after harvest and storage. Within a few months, stored hay loses nearly all its vitamin E content, making supplementation necessary for horses without consistent pasture access.

Hay loses vitamin E rapidly as it is dried, baled, and stored for long periods. Photo by filmbildfabrik/Adobe Stock

“For horses that don’t have regular pasture turnout, diets can be supplemented with vitamin E,” Fenn continues. “These supplements come from either natural or synthetic sources. Synthetic products are labeled dl-alpha-tocopherol, all racemic, or all-rac vitamin E, and I would not recommend using them. Supplements made from natural sources contain 100 percent RRR-alpha-tocopherol. They may also be labeled as d-alpha-tocopherol. Studies have shown that the natural formulations successfully raise vitamin E levels in horses, and I would always support using them for supplementation over synthetic products.

“There’s a lot of misinformation out there,” says Fenn. “Natural formulations can either be in water-soluble (tocopherol) or powdered/pellet forms (tocopheryl). The main difference between the two is how quickly you should expect to see a clinical response in your horse. It’s fast with water-soluble formulations—you can see a difference in as little as 24 to 48 hours. In comparison, the powdered/pellet formulations can take up to eight to 10 weeks before you might notice a change.”

You may need to add vitamin E to your supplement lineup if your horse doesn’t graze enough to get adequate levels of this important nutrient. Photo by Dusty Perin

Vitamin E Deficiency

Horses that do not receive enough vitamin E can develop serious health issues. Symptoms of vitamin E deficiency include muscle weakness and stiffness, poor performance and prolonged recovery times, neurological issues, muscle fasciculations (twitching), poor body condition, weight loss, muscle atrophy and lethargy, and weakened immune response.

These can all be brought on by limited access to pasture, changes in climate, and modern equine management practices.

Long-Term Effects of Deficiency

“There are three primary disorders associated with vitamin E deficiency in horses,” says Fenn. “Vitamin E responsive myopathy (VEM), equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM), and equine motor neuron disease (EMND).

“Although all three are associated with the same deficiency, they have different clinical presentations and manifest at different ages in affected horses,” she continues. “VEM and EMND cause neuromuscular disease, which presents as an insidious onset of poor performance, muscle weakness, and sometimes even muscle atrophy and fasciculations (twitching). eNAD/EDM affects the central nervous system of young to middle-aged horses, causing limb incoordination (ataxia), an abnormal stance, behavioral changes and occasionally loss of conditioning. Of the three disorders, horses with VEM respond remarkably well to appropriate vitamin E supplementation and can make a complete recovery. Unfortunately, EMND has a much more guarded prognosis, even with supplementation. There is no treatment available for eNAD/EDM.

“Understanding the different forms of vitamin E and planning supplementation appropriately is currently our only approach to preventing these diseases.”

When choosing to supplement your horse, there are several variables to consider: type of supplement, dose, length of treatment, and any clinical signs associated with a deficiency. A simple blood test performed by your veterinarian can measure the current levels of vitamin E and help answer some of the above questions to determine the best course of treatment for your horse.

Measuring Your Horse’s Vitamin E Levels

If you want to make sure your horse is consuming adequate amounts of this critical nutrient, here are some recommended daily intake levels from the National Research Council (NRC):

◆ 500-1000 IU per day for maintenance horses

◆ 800-1,000 IU per day for performance horses

◆ 1,500-5,000 IU per day for horses with muscle disorders or neurological conditions.

“The NRC requirements do not discriminate between natural and synthetic sources,” Fenn cautions. “They don’t factor in if your horse has a deficiency, increased performance demands, or medical conditions. Horses in consistent training, those with medical conditions, or those in geographic areas with no access to pasture typically require higher doses under veterinary guidance.”

If your horse has been diagnosed with a deficit by your veterinarian, a natural water-soluble (not powder/pellets) form of vitamin E at 10 IU per kilogram of body weight is recommended. Periodic rechecks are equally important to help guide long-term treatment.

Signs of Over-Supplementation

Over-supplementation of fat-soluble vitamins (A, D, E and K) is possible, since excess cannot be excreted in the urine like with water-soluble vitamins (vitamin C and the B vitamins), and can lead to potential health risks.

Moderation and veterinary consultation are critical when adjusting vitamin E levels to avoid unintended health complications. Signs of excessive vitamin E intake include coagulopathy, in which the blood’s ability to coagulate (form clots) is impaired, and diminished bone mineralization.

Despite the vast array of choices and marketing that accompany the world of equine supplements, vitamin E is a foundational pillar for equine health. Don’t let deficiencies take root, and make sure this key element is reaching your horse at sufficient levels in his diet.

This article about vitamin E for horses appeared in the July/August 2025 issue of Horse Illustrated magazine. Click here to subscribe!

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