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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.
What's your top priority with your horse's health?
What's your top priority with your horse's health?
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.
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 minimum of 1200 IUs of vitamin E daily.
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]
Frequently Asked Questions
Here are some frequently asked questions about vitamin E supplementation in horses:
Horses need vitamin E because it is an essential antioxidant that helps protect cells from oxidative stress. It supports immune function, helps maintain cell membrane integrity, and plays an important role in muscle health and recovery. Horses cannot make vitamin E on their own, so they must get it from the diet. This makes daily intake especially important in horses with higher physical demands.
Horses are most likely to need vitamin E supplementation when they do not have regular access to fresh pasture. Horses in moderate to heavy work, growing horses, lactating mares, and senior horses are also more likely to benefit from additional vitamin E. These horses either have higher requirements or are more likely to fall short on forage-based intake alone. Supplementation is often most important when fresh grass is limited.
Vitamin E helps muscles and exercise recovery in horses by reducing oxidative stress created during work. It helps protect muscle cells from damage and supports normal muscle function after exertion. This is one reason vitamin E is often emphasized in exercising horses and in horses recovering from muscle problems. Adequate intake supports both performance and comfort.
Signs of vitamin E deficiency in horses can include muscle wasting, weakness, poor performance, and certain muscle diseases. Deficiency is also associated with neurological conditions such as Equine Motor Neuron Disease and Equine Degenerative Myeloencephalopathy. In some horses, vitamin E depletion may also be a concern with tying-up episodes. Because the effects can be serious, deficiency should be addressed promptly.
Low vitamin E can contribute to neurological disease in horses because this vitamin plays a protective role in nervous system tissues. Inadequate intake has been linked with Equine Motor Neuron Disease and Equine Degenerative Myeloencephalopathy. These conditions can significantly affect movement, performance, and quality of life. This is one reason vitamin E status matters so much in horses with neurological concerns.
The best form of vitamin E for horses is usually the natural form, d-alpha-tocopherol, also called RRR-alpha-tocopherol. This form is considered the most biologically active and most bioavailable. Synthetic vitamin E, called dl-alpha-tocopherol, contains a mixture of forms that do not all work the same way in the body. When choosing a supplement, the natural form is generally preferred when strong absorption and effectiveness are the priority.
The difference between natural and synthetic vitamin E for horses is mainly in chemical structure and biological activity. Natural vitamin E is the plant-derived form that horses would normally get from fresh grass, while synthetic vitamin E is a manufactured mixture of several different forms. Some of those synthetic forms have biological activity, but not all are equally useful. For this reason, natural vitamin E is generally considered the better option for supplementation.
Hay usually does not provide enough vitamin E for horses, especially when it makes up most of the diet. Fresh pasture contains the highest concentrations of natural vitamin E, while hay can lose much of its vitamin E during drying and storage. In some cases, hay may contain very little or even none at all. Horses on hay-based diets often need another source to meet their requirements.
Some horses do benefit from more than the minimum vitamin E requirement, especially when their workload, age, or health status creates greater oxidative stress. The minimum requirement is designed to prevent clear deficiency, but it may not represent the most supportive intake for every horse. Senior horses, for example, may benefit from higher supplementation in some situations. This is why vitamin E planning should consider the whole horse, not just the minimum number.
Owners should decide how much vitamin E to supplement by looking at the horse's full diet, body weight, life stage, and work level. The key question is how much vitamin E the horse is already getting from pasture, hay, and fortified feeds before adding more. This helps avoid guessing and makes supplementation more targeted. A balanced diet review is often the best starting point before choosing a product or dose.
Vitamin E supplementation is generally safe for horses when it is used appropriately and as part of a balanced feeding program. The bigger concern is usually under-supplying horses that have limited pasture access or increased needs, rather than modest supplementation itself. Still, supplementation should fit the horse's overall diet rather than being added blindly. Choosing the right form and evaluating the full ration helps make supplementation both safer and more effective.
Summary
Vitamin E is an essential antioxidant for horses, supporting immune health, muscle integrity, and recovery from oxidative stress. Supplementation is often required when pasture access is limited or during periods of growth, lactation, or intense exercise.
- Vitamin E is a key antioxidant for immune response and muscle recovery
- Natural forms (RRR-alpha-tocopherol) are more bioavailable than synthetic
- Horses on hay diets typically require vitamin E supplementation
- Deficiency is linked to EMND, EDM, and white muscle disease
- Minimum requirement is 1 IU/kg, but higher amounts benefit many horses
- Fat in the diet enhances vitamin E absorption
References
- National Research Council Nutrient Requirements of Horses: Sixth Revised Edition. 2007.
- Jensen, S.K. and Lauridsen, C. Alpha-tocopherol stereoisomers. Vitam Horm. 2007.
- Desmarchelier, C. and Borel, P. Bioavailability of vitamin E in humans. HAL open science. 2018.
- 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
- Shastak, Y. et al. A Century of Vitamin E: Early Milestones and Future Directions in Animal Nutrition. Agriculture. 2023.
