Does your horse need a Vitamin E supplement added to his or her feeding program?
Hay is the most important component of a horse’s diet, and contributes almost all the necessary macronutrients (protein, fat and carbohydrates) and micronutrients (vitamins and minerals) that our horses need.
Notice how I said almost? Hay does not cover all our horsesâ€™ nutrient requirements and there is one micronutrient in particular that is often deficient in horses on a hay-based diet.
That essential nutrient is vitamin E.
What is Vitamin E?
Vitamin E is an antioxidant involved in immune response, muscle function, and cellular health.
It acts as an antioxidant to neutralize free-radicals that are produced naturally during the metabolism of fat into energy. These free-radicals are volatile in nature and can cause damage to cell membranes, enzymes and other intracellular components.
Vitamin E and other anti-oxidants such as selenium play critical roles in maintaining a balance, or homeostasis, with free-radicals.
This fat-soluble vitamin is an especially important micronutrient for the health of growing and exercising horses, but is also vital for adult horses.
Vitamin E deficiencies have been associated with neuromuscular conditions such as equine degenerative myeloencephalopathy or equine motor neuron disease. 
While these conditions are rare, in order to optimize our horseâ€™s nutrition, we need to ensure they are getting enough vitamin E to support their overall health and wellbeing.
Types of Vitamin E
The term ‘Vitamin E’ describes a family of eight structures that can be divided into two groups – tocopherols and tocotrienols – depending on their structural formation.
Typically, in feed formulations, we most often see vitamin E in the form of alpha-tocopherol as this is the most bioavailable form.
Equine dietary supplements will use both natural and synthetic forms of alpha-tocopherol. The natural forms of Vitamin E are superior because they have better absorption in the body and are better used in your horse’s cells.
Natural forms of this vitamin will be listed with a “d” prefix, like d-alpha-tocopherol, d-alpha tocopheryl acetate or d-alpha tocopheryl succinate. If you see a “dl” prefix, this is a synthetic form of Vitamin E, such as dl-alpha tocopherol.
When should you supplement Vitamin E?
You may have heard that horses are more likely to require Vitamin E supplementation during the wintertime. Why is supplementation especially important in the winter?
Vitamin E is an essential nutrient, meaning is it unable to be synthesized by the body and must be obtained through the diet.
For horses, the main dietary source of vitamin E comes from fresh, green grass. Unfortunately, during the winter most horses do not have access to fresh pasture due to season, location and metabolic concerns. This puts them at greater risk for being deficient in vitamin E.
Vitamin E is also unstable in grass. As the grass matures or once it is cut and dried into hay, the level of vitamin E rapidly degrades leaving little to no vitamin E left by the time it is consumed by the horse.
In fact, 60% of the vitamin E in hay degrades just four days after cutting. This figure continues to drop drastically the longer the hay is in storage until there is virtually none of this vitamin left. This means our horses need to obtain their vitamin E from another source!
Other Reasons to Supplement Vitamin E
Wintertime is not the only time to consider the vitamin E intake in our horsesâ€™ diets. There are 5 key factors we need to consider when deciding when to supplement our horse with vitamin E.
In particular, you should ensure your horse is receiving enough vitamin E when your horse is:
- On a predominantly or entirely hay-based diet
- In moderate to heavy work
- On a high fat diet
- Diagnosed with a neurological disorder
- On a diet containing low levels or synthetic vitamin E
As always, consult a qualified equine nutritionist or a veterinarian before adding new supplements to your horseâ€™s diet. You can submit your horseâ€™s diet for analysis online and one of our nutritionists will be happy to provide a complementary evaluation.
In most cases, your horse will benefit more from being on a complete mineral and vitamin supplement than from feeding Vitamin E in isolation.
Mad Barn’s Omneity and AminoTrace+ ration balancers both contain high levels of vitamin E to help cover your horseâ€™s dietary requirements. They also contain a complete array of other essential minerals and vitamins required to meet core nutritional needs for every horse.
What to look for in an Equine Vitamin E Supplement?
As mentioned previously, the main form of vitamin E we see in feed formulations is alpha-tocopherol-acetate and this can be found in two forms: natural (d-alpha-tocopherol) and synthetic (dl-alpha-tocopherol).
In commercial feeds and supplements, the synthetic form of vitamin E is most commonly found due to its longer shelf-life and stability. However, synthetic vitamin E has been demonstrated to be less bioavailable than natural vitamin E. 
Previously, it was suggested that you would have to feed three times as much synthetic vitamin E than you would natural vitamin E. However, researchers out of the University of Georgia compared in impact of synthetic and natural vitamin E on increasing blood levels of alpha-tocopherol and potentially helping to reduce oxidative stress and muscle damage in horses. 
Interestingly, this researched demonstrated that natural vitamin E is superior in increasing blood levels of vitamin E when compared to four times the amount of synthetic vitamin E.
Many horses at risk of Vitamin E deficiency also require additional selenium in their diet. These two nutrients are antioxidants that work together to rid cells of reactive oxygen species, protecting tissues from damage that arises from high-intensity exercise and disease.
How to Feed Vitamin E?
According to the NRC’s Nutrient Requirements of Horses, a mature horse at maintenance requires 1 International Unit (IU) of Vitamin E per kilogram of body weight.  A typical 500 kg (1100 lb) horse would require 500 IUâ€™s of vitamin E per day.
This requirement is different for horses based on work load, physiological status (i.e. growing, breeding), presence of disease or existing vitamin E deficiency.
Growing foals, broodmares and heavily exercised horses will require 2 IU per kilogram of body weight per day. For example, a 600 kg exercising horse will need 1200 IU of vitamin E provided by their diet every day.
Can you feed too much Vitamin E? As this vitamin is fat-soluble and does not get excreted as readily as water-soluble vitamins, it is important to be aware of toxicity levels.
However, studies have shown that up to 10,000 IU per day is safe for horses, particularly in the instances of neuromuscular disorders. High dosages of any vitamin or mineral should only be done under the guidance of a qualified equine nutritionist or veterinarian.
Before adding a vitamin E supplement to your horseâ€™s diet, we recommend you evaluate your feeding program to determine how much Vitamin E is being provided by current dietary sources. This will save you money in the long run and ensure that your horse is receiving a balanced diet that meets his or her nutrient requirements.
Mad Barn can help you conduct a thorough diet evaluation and create an optimal feeding plan that addresses your horseâ€™s individual needs. Contact us for a complementary diet analysis and one of our equine nutritionists will be happy to help.
- Vitamin E is an essential antioxidant in horses and is important for neurological function, muscle function and cellular health
- Diet and workload are important factors in determining if your horse needs a vitamin E supplement
- Look for supplements containing natural vitamin E (d-alpha-tocopherol) as this is the most bioavailable form of vitamin E
- Read more about the effects of feeding vitamin E in horses in our article on the top 8 Science-Backed Benefits of Vitamin E in Horses
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- Finno, CJ and Valberg, SJ. A Comparative Review of Vitamin E and Associated Equine Disorders. J Vet Intern Med. 2012.
- Fagan, MM et al. Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses. Journal of Equine Vet Med. 2020.
- NRC, 2007 Nutrient Requirements of Horses: Sixth Revised Edition. National Research Council. 2007.