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 only be used in order 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:

  • Not consuming pasture year-round
  • Undergoing moderate-heavy exercise
  • Growing
  • Lactating

An equine vitamin E deficiency can contribute to muscle pathologies like Exertional Rhabdomyolysis (tying-up syndrome), white muscle disease, and neurological diseases such as Equine Motor Neuron Disease (EMND) and Equine Degenerative Myeloencephalopathy (EDM).

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.

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. 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 is identical to natural vitamin E.  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.

How Much Vitamin E Does My Horse Need?

Vitamin E is measured in IU’s, 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 IU’s of vitamin E per day.

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 1200 IUs of vitamin E daily.


Calculate Your Horse’s 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 1380 IU’s would need to be acquired through other feedstuffs or a concentrated vitamin E supplement.

Before supplementing vitamin E in your horse’s diet, be sure to conduct an evaluation of 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 can help you conduct a thorough diet evaluation and create an optimal diet that addresses your horse’s individual needs. Contact Mad Barn today.

Is Your Horse's Diet Missing Anything?

Identify gaps in your horse's nutrition program to optimize their well-being.


  1. National Research Council. Nutrient requirements for horses, National Academy Press, Washington, D.C., USA, 2007