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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 horses’ 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, metabolism, and cellular health.
It acts as an antioxidant to neutralize free radicals that are produced naturally during metabolism of sugars and fat into energy. These free radicals are volatile in nature and can cause damage to cell membranes, enzymes and other intracellular components.
Vitamin E, vitamin C 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 pregnant, lactating, breeding, growing and exercising horses, but is also vital for all adult horses.
Vitamin E deficiencies have been associated with neuromuscular conditions such as: [1]
- White muscle disease
- Neuraxonal dystrophy
- Pigment retinopathy
- Vitamin E deficiency myopathy
- Masseter muscle atrophy in adults
- Equine degenerative myeloencephalopathy
- Equine motor neuron disease
Some of these conditions, such as white muscle disease, are also associated with both selenium and vitamin E deficiency.
While these conditions are rare, in order to optimize our horse’s nutrition, we need to ensure they are getting enough vitamin E (and selenium) to support their overall health and wellbeing.
Vitamin E status
The best way to determine your horse’s vitamin E status is with a blood test.
Horses grazing good pasture, which is abundant in vitamin E, have serum levels of 3 to 6 ug / mL. [2] Therefore, blood vitamin E levels within this range would be considered adequate.
Horses that are not grazing are at risk of becoming vitamin E deficient because this nutrient is lost during hay storage. Indeed, blood tests have shown lower levels of vitamin E in horses on hay and alfalfa pellets (2.8 ug / mL), compared to horses on pasture (4.2 ug / mL). [3]
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 form preferred by the body.
Any of the tocopherols or tocotrienols may be absorbed in the gut but the liver preferentially packages and secretes alpha-tocopherol for the tissues.
Natural vs Synthetic Vitamin E
Equine dietary supplements will use natural and synthetic forms of alpha-tocopherol. The natural forms of Vitamin E are superior because they have higher biological activity. Natural and synthetic forms are absorbed equally well by the gut but the liver preferentially secretes natural vitamin E for the rest of the body to use. [4]
On a feed tag, 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.
In feeds and supplements, alpha-tocopherol is typically bound to acetate or succinate forms for better stability and a longer shelf-life.
What's your top priority with your horse's health?
What's your top priority with your horse's health?
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 it is 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.
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.
On average hay has 85% less vitamin E than fresh grass. [5] 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 horses’ 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 polyunsaturated fat diet [6]
- Diagnosed with a neurological or muscular disorder
- Breeding stock and growing horses
As always, consult a qualified equine nutritionist or a veterinarian before adding new supplements to your horse’s diet. You can submit your horse’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 AminoTrace+ vitamin and mineral supplement contains high levels of natural vitamin E to help meet your horse’s dietary requirements. AminoTrace+ also contains 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, alpha-tocopherol is the main vitamin E found in feeds and supplements. This can be found in two forms: natural (d-alpha-tocopherol) and synthetic (dl-alpha-tocopherol).
Of these, synthetic vitamin E is less bioactive than natural vitamin E. [7]
Researchers out of the University of Georgia compared the 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. [7]
Interestingly, they showed that 4,000 IU of natural vitamin E increased blood levels by 77% compared to a 33% increase with 4,000 IU of synthetic vitamin E. [7] This is similar to the common recommendation to feed twice as much synthetic as natural vitamin E.
Mad Barn’s Natural E/Organic Se pellets and bulk Vitamin E powder supplement as well as our AminoTrace+ ration balancer contain natural forms of vitamin E, d-alpha-tocopherol. Mad Barn’s omega-3 fatty acid supplement w-3 oil is also fortified with natural 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. [8] A typical 500 kg (1,100 lb) horse would require 500 IU of vitamin E per day.
This requirement is different for horses based on workload, 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 1,200 IU of vitamin E provided by their diet every day.
When to provide more vitamin E
There are many situations where the horse can benefit from receiving more than the minimum vitamin E.
Young horses are particularly susceptible to the effects of vitamin E deficiency. [9][10]
Supplementing broodmares with 2,500 IU of vitamin E in the last month of pregnancy improved immunoglobulin levels in their colostrum and enhanced vitamin E and antibody levels in their foals. [11]
Young Quarter Horses affected by neuroaxonal dystrophy have been found to have a faster rate of metabolism of vitamin E. [12] To decrease the risk of this disease, it has been recommended that broodmares receive 5,000 IU vitamin E during pregnancy and foals be supplemented with 500 IU/day starting at birth. [2]
Vitamin E has been clearly shown to ameliorate the oxidative stress associated with exercise. Horses in work should also be supplemented with at least 1,800 IU natural vitamin E per day. [13]
Supplementing Vitamin E along with Fat
Because vitamin E is a fat-soluble vitamin, it requires fat from the diet and bile to be absorbed. Vitamin E in fresh grass is already associated with fats in the membranes of cells and organelles.
Based on studies in humans, absorption of supplemental vitamin E increases when more fat is added to the meal. [14] Similarly, in a study of non-exercising growing horses fed recommended levels of vitamin E, adding oil increased blood alpha-tocopherol levels. [15]
It remains to be seen whether a difference would be observed in exercising horses, where vitamin E requirements are higher.
This makes w-3 oil an excellent choice for vitamin E supplementation. A typical serving of 100 ml (3.5 oz) provides 1,500 mg of the anti-inflammatory fatty acid DHA, and 1,500 IU of natural vitamin E.
If you need more vitamin E than provided by the amount of oil you are feeding, mix powdered vitamin E into it before serving or use the oil to soak pellets.
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.
Although high intakes are considered safe, the NRC has set a safe upper limit of vitamin E for horses at 10,000 IU per day. 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 horse’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 horse’s individual needs. Submit your horse’s diet for analysis and one of our equine nutritionists will be happy to help.
Frequently Asked Questions
Here are some frequently asked questions about vitamin E for horses:
Horses need vitamin E because it is an important antioxidant that helps protect cells from damage caused by free radicals. It also supports immune function, normal metabolism, and overall cellular health. Vitamin E is especially important for muscle and nerve tissues, which are highly sensitive to oxidative stress. While every horse needs it, growing, breeding, pregnant, lactating, and exercising horses often have a greater need for adequate intake.
Vitamin E works in a horse's body by helping neutralize free radicals that are produced during normal energy metabolism. This protection helps limit damage to cell membranes, enzymes, and other structures inside cells. Vitamin E also works alongside other antioxidants, including selenium and vitamin C, to support tissue health. Its role is particularly important in maintaining healthy muscles, nerves, and immune defenses.
Horses on hay-based diets are often low in vitamin E because fresh green grass is the main natural source of this nutrient. Once grass matures or is cut and dried into hay, vitamin E levels drop quickly during storage. By the time hay is fed, much of the original vitamin E may already be gone. That is why horses without regular pasture access are at greater risk of deficiency.
Not all horses need a vitamin E supplement because pasture access can provide enough for some individuals. Horses that graze good-quality fresh grass usually have better vitamin E status than horses fed mostly hay. Supplementation becomes more important when pasture is limited, especially in winter or for horses with higher demands. The need depends on the whole diet, workload, life stage, and health status rather than one simple rule.
Horses most likely to need extra vitamin E include those on mostly hay diets, horses in moderate to heavy work, and horses eating higher-fat diets rich in polyunsaturated fat. Growing horses, breeding horses, pregnant mares, and lactating mares may also need more support. Horses with neurological or muscular disorders are another group that deserves careful attention to vitamin E intake. These situations increase the chance that basic forage alone will not fully meet the horse's needs.
Signs of vitamin E deficiency in horses can include muscle problems, poor performance, and neurological changes. Low vitamin E status has been associated with conditions such as white muscle disease, vitamin E deficiency myopathy, equine degenerative myeloencephalopathy, and equine motor neuron disease. Some horses may also show issues related to weakness or muscle wasting. Because these problems can have more than one cause, diagnosis should not rely on signs alone.
The best way to tell if a horse is low in vitamin E is through a blood test. Blood testing gives a clearer picture of vitamin E status than guessing based on diet alone. Horses on fresh pasture tend to have higher blood levels than horses eating hay or alfalfa pellets without pasture access. Testing is especially useful when a horse has higher needs or is showing muscle or nerve-related concerns.
Natural vitamin E is better for horses because it has higher biological activity than synthetic vitamin E. Both forms can be absorbed from the gut, but the horse's body is better at using the natural form once it is processed by the liver. On labels, natural vitamin E usually appears with a "d" prefix, while synthetic forms use a "dl" prefix. When choosing a supplement, that difference matters because it affects how effectively the horse can use the product.
How much vitamin E a horse needs depends on body weight, workload, age, reproductive status, and whether there is an existing deficiency or health concern. Horses at maintenance generally need less than growing, breeding, or heavily exercised horses. Needs can also rise when the diet contains more fat or when a horse is under higher oxidative stress. The most practical approach is to assess the full feeding program before deciding how much additional vitamin E is appropriate.
Vitamin E should often be fed with fat because it is a fat-soluble vitamin and fat helps support its absorption. Fresh grass naturally provides vitamin E alongside plant fats, which may help explain why pasture is such an effective source. Supplemental vitamin E may be better utilized when included in a meal that contains some dietary fat. This is one reason vitamin E is sometimes paired with oil-based feeding programs.
Too much vitamin E can be a concern because it is a fat-soluble vitamin and is not cleared from the body as easily as water-soluble vitamins. High intakes are generally considered safe, but there is still a recognized upper safe limit. Large doses should only be used with guidance from a veterinarian or qualified equine nutritionist. Reviewing the whole diet first helps avoid unnecessary supplementation and keeps the feeding program balanced.
A complete vitamin and mineral supplement is often better than vitamin E alone when a horse's overall diet needs broader support. Many horses that are low in vitamin E may also benefit from a more balanced intake of other essential nutrients rather than adding one nutrient in isolation. This approach can be more effective for covering core nutritional gaps in hay-based diets. Choosing between a single-nutrient product and a more complete supplement depends on what the rest of the feeding program already provides.
Summary
- 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
References
- Finno, CJ and Valberg, SJ. A Comparative Review of Vitamin E and Associated Equine Disorders. J Vet Intern Med. 2012. View Summary
- Finno, C.J. Vitamin E: Key to Equine Health. UC Davis. 2018.
- Habib, H. et al. Simultaneous quantification of vitamin E and vitamin E metabolites in equine plasma and serum using LC-MS/MS. J Vet Diagn Invest. View Summary
- Burton, G.W. et al. Human plasma and tissue alpha-tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E. Am J Clin Nutr. 1998.
- Zeyner, A. Harris, P. 9 - Vitamins. Equine Applied and Clinical Nutrition. 2013.
- Philip, H. and Norris, E. Quantitative Consideration of the Effect of Polyunsaturated Fatty Acid Content of the Diet Upon the Requirements for Vitamin E. Am J Clin Nutr. 1963.
- Fagan, M.M. et al. Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses. J Equine Vet Med. 2020. View Summary
- NRC, 2007 Nutrient Requirements of Horses: Sixth Revised Edition. National Research Council. 2007.
- Finno, C.J. et al. Concurrent Equine Degenerative Myeloencephalopathy and Equine Motor Neuron Disease in Three Young Horses. J Vet Intern Med. 2016. View Summary
- Donnelly, C.G. and Finno, C.J. Vitamin E depletion is associated with subclinical axonal degeneration in juvenile horses. Equine Vet J. 2023. View Summary
- Bondo, T. et al. Administration of RRR-?-tocopherol to pregnant mares stimulates maternal IgG and IgM production in colostrum and enhances vitamin E and IgM status in foals. J Anim Physiol Anim Nutr (Berl). 2011. View Summary
- Hales, E.N. et al. Increased a-tocopherol metabolism in horses with equine neuroaxonal dystrophy. J Vet Intern Med. 2021. View Summary
- Svete, A.N. et al. Effects of Vitamin E and Coenzyme Q10 Supplementation on Oxidative Stress Parameters in Untrained Leisure Horses Subjected to Acute Moderate Exercise. Antioxidants (Basel). 2021. View Summary
- Desmarchelier, C. and Borel, P. Bioavailability of vitamin E in humans. Elsevier Science. 2017.
- Siciliano, P.D. and Wood, C.H. The effect of added dietary soybean oil on vitamin E status of the horse. J Anim Sci. 1993. View Summary
