Vitamin E, or alpha-tocopherol, is an essential vitamin that must be obtained through your horse’s diet. There are many products sold in the equine supplement industry that contain varying forms of vitamin E that are available, but it is sometimes difficult to decide which type and how much is best for your horse and its individual needs.

Ultimately, the most bio-available forms of vitamin E should be used to properly formulate balanced equine diets to treat vitamin E deficiency and its associated conditions and to aid in exercise recovery.

Calculating how much vitamin E to give to your horse can be done by looking at your horse’s body weight, physiological status and work level.

The Importance of Vitamin E

Vitamin E has a vital role in your horse’s body as a powerful antioxidant that enhances the immune response, maintains cell membrane integrity and reduces oxidative stress brought on by exercise.

The changes that humans have made in the modern equine diet as well as advances that have been made in equine physiology have warranted vitamin E supplementation, especially for horses that are:

Insufficient vitamin E intake can contribute to muscle pathologies such as vitamin E deficiency myopathy with muscle wasting and weakness, white muscle disease, and neurological diseases such as Equine Motor Neuron Disease (EMND) and Equine Degenerative Myeloencephalopathy (EDM).

Vitamin E depletion could easily develop in horses with exertional rhabdomyolysis (tying-up) of any cause and supplementation is routinely done in those cases.

It is also a major antioxidant in the immune system and increased supplementation to combat oxidative stress in horses with nervous system infections is reasonable.

These conditions can significantly reduce equine performance and welfare and so the prompt detection of a deficiency and nutritional or medical intervention is extremely important.

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Not all Vitamin E is Created Equal

There are many options available when it comes to supplementing vitamin E.  Vitamin E is a generic term to describe the eight fat-soluble compounds that include four tocopherols and four tocotrienols; of these eight compounds, alpha-tocopherol is the most biologically active and relevant form. The most natural form of alpha-tocopherol is termed d-alpha-tocopherol, also known as RRR-alpha-tocopherol. It is only synthesized in plants, and so it must be obtained through the diet.

Fresh grass pasture contains the highest concentrations of d-alpha-tocopherol, however, a large number of horses do not have year-round access to grass pasture and their diets consist mostly of hay.

Synthetic alpha-tocopherol differs from natural alpha-tocopherol due to its chemical structure and origin. The synthetic form, dl-alpha-tocopherol, contains a mixture of eight stereoisomers of alpha-tocopherol, one of which, the RRR, is identical to natural vitamin E. Some of the other stereoisomers also have some biological activity but this apparently varies by tissue and species. [2]

Confused yet?  Not to worry, the biological activity of different forms of vitamin E is standardized with the international unit (IU).

Since free vitamin E compounds are not stable, the esterified forms of synthetic and natural alpha-tocopherol, dl-alpha-tocopheryl acetate and d-alpha-tocopheryl acetate, respectively, are typically used in feed and supplement formulation.

Vitamin E

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  • Optimal antioxidant protection
  • Supports exercise recovery
  • Supports immune function
  • Natural with high bioavailability

How Much Vitamin E Does My Horse Need?

Vitamin E is measured in IUs, or International Units. The National Research Council that published the Nutrient Requirements of Horses in 2007 states that the vitamin E requirement for a mature horse at maintenance is 1 IU per kg of body weight , [1] For the average 500 kg horse, this would then work out to be a requirement of 500 IUs of vitamin E per day. This is the bare minimum needed to prevent full blown deficiency.

This requirement will change depending on physiological status (exercising, growing, breeding etc.), work load and the presence of disease or vitamin E deficiency. For foals, broodmares and exercising horses, for example, the requirement increases to 2 IU per kg body weight.

As an example, a 600 kg horse, undergoing heavy exercise and consuming 2% of its body weight in dry matter (12 kg) per day, requires a minumum of 1200 IUs of vitamin E daily.


Calculate Your Horse’s Minimum Vitamin E Requirement


Vitamin E required: IU/day

**Based on a mature horse at maintenance (not exercising).


A typical timothy grass hay, alone, contains only 5-25 IU per kg, and so 12 kg (average ~ 15 IU) would equal 180 IUs of vitamin E. The remaining 1020 IUs would need to be acquired through other feedstuffs or a concentrated vitamin E supplement.

That’s assuming the hay even has that much vitamin E. Hay can have up to 85% less vitamin E than pasture. It may even have none and we are still talking about bare minimum requirements of a very important vitamin. [5]

Many horses can benefit from supplementation above the minimum recommended by the NRC. For example, seniors supplemented with 15 IU/kg (7500 IU for a 500 kg horse) showed improvement in immune function and a stronger response to vaccination. [4]

Before supplementing vitamin E in your horse’s diet, be sure to evaluate your horse’s whole diet to see where existing sources of vitamin E are coming from. This will save you money and ensure that your horse is first receiving a balanced diet that meets its nutrient requirements.

Mad Barn’s w-3 Oil with added natural vitamin E is a good place to start as vitamin E absorption is enhanced by fat. [3]

w-3 Oil

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  • Promotes joint comfort
  • Helps to fight inflammation
  • Skin & coat condition
  • Palatable source of Omega-3's

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  1. National Research Council Nutrient Requirements of Horses: Sixth Revised Edition. 2007.
  2. Jensen, S.K. and Lauridsen, C. Alpha-tocopherol stereoisomers. Vitam Horm. 2007.
  3. Desmarchelier, C. and Borel, P. Bioavailability of vitamin E in humans. HAL open science. 2018.
  4. Petersson, K.H. et al. The influence of vitamin E on immune function and response to vaccination in older horses. J Anim Sci. 2010. View Summary
  5. Shastak, Y. et al. A Century of Vitamin E: Early Milestones and Future Directions in Animal Nutrition. Agriculture. 2023.