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Vitamin E is a fat-soluble vitamin that acts as an important antioxidant for horses. It helps maintain a healthy immune system and supports normal nerve and muscle function.
Horses need vitamin E in their diet because they cannot synthesize it endogenously in their body. It is found in fresh, green grasses and forages. Horses that are mostly on lush pasture will get enough vitamin E by grazing fresh grass.
Cutting grasses and forages to harvest hay causes rapid degradation of vitamin E that continues as the hay is stored. Hay stored for longer periods of time or poor-quality hay will have lower vitamin E content. If your horse is fed mostly hay, they likely have low vitamin E intake.
Vitamin E deficiency in horses can cause them to be more likely to tie-up after exercise. They might be sick with frequent coughs and colds and recover slowly. Insufficient Vitamin E in the diet can make some equine neurological disorders worse.
Mad Barn’s Omneity Premix is a fully balanced equine mineral and vitamin supplement that provides comprehensive nutritional coverage for your horse’s needs. It contains 8,500 IU per kg Vitamin E (dl-alpha-tocopherol), sufficient to meet the needs of most horses.
We also carry bulk natural Vitamin E powder (405,000 IU per kg) for horses that require higher levels.
Vitamin E and selenium are necessary for optimal antioxidant protection because they support the function and formation of glutathione peroxidase, the main antioxidant enzyme found in all cells of the body. Mad Barn’s Natural E/ Organic Se pellet provides both of these key nutrients in natural, organic forms with high bioavailablity.
Why Horses Need Vitamin E
Vitamin E is a shared term used to encompass eight compounds – tocopherols (saturated) and tocotrienols (unsaturated). Tocopherols and tocotrienols have four structural variants called alpha, beta, gamma, and delta. Alpha-tocopherol is the most abundant and most bioavailable in horse feeds.
Antioxidants like vitamin E protect cells from free radicals. Free radicals are unstable molecules that steal electrons from other molecules to become stable, causing the other molecules, like DNA and cell membranes, to become unstable.
Free radicals are naturally produced when horses metabolize carbohydrates, fat, or protein to make energy. Free radicals are not completely bad. A small amount are needed to help cells respond to signals in the body.
However, too much free radical damage, called oxidative stress, damages cells often to the point of cell death. This will cause organs and tissues like the liver and muscles to not function properly and negatively impact the horse’s health, resulting in premature aging.
Antioxidants are compounds that neutralize free radicals before they cause damage. Antioxidants come in many forms. Vitamins (vitamin E and C), minerals (selenium) and enzymes (glutathione peroxidase) all work together to provide optimal antioxidant protection.
Oxidative damage from having low antioxidant status or high free radical burden can present itself in horses as muscle soreness after exercise, slow recovery from illness, or frequent illness.
Feeding adequate amounts of Vitamin E and other natural antioxidants can ensure your horse has appropriate antioxidant defense. Getting enough of this vitamin in the diet is particularly important for equine athletes.
Vitamin E Benefits for Horses
Below are the top 8 benefits of vitamin E in horses:
- Vitamin E eases muscle soreness and stiffness in exercising horses, helping them sustain high levels of activity.
- Having adequate intake of this vitamin will help muscles recover after exercise which can support athletic performance. [1]
- Horses with adequate vitamin E intake are less likely to experience chronic tying up (exertional rhadomyolysis).
- Vitamin E boosts the immune response, enhancing the bacteria killing capacity of immune cells. This helps horses recover from illness quickly. [2]
- Vitamin E can help horses with insulin resistance. According to Dr. Nicholas Frank at the University of Tennessee, daily intake of 1000 IU could help improve insulin sensitivity.
- Having adequate antioxidant defenses can minimize stress and health issues related to travel and competition, helping your horses stay healthy and ready to compete. [4]
- It can prevent or minimize the effects of neurological disorders like equine motor neuron disease (EMND) and equine degenerative myeloencephalopathy (EDM) from developing. [3]
- Horses with polysaccharide storage myopathy (PSSM), also known as equine polysaccharide storage myopathy (EPSM) have a higher burden of oxidative stress. Vitamin E could help horses with this muscular disorder.
Vitamin E Research Results
Supplementation for Exercise Recovery
A study by Fagan et al., 2017 examined the effect of vitamin E supplementation on oxidative stress in exercising horses. They studied natural and synthetic forms of vitamin E at two different doses.
After 6 weeks, horses receiving 4000 IU per day of natural vitamin E (d-alpha-tocopherol) had lower serum AST (aspartate aminotransferase) than those fed 4000 IU or 1000 IU per day of synthetic vitamin E. Serum AST is an indicator of muscle damage in horses. When levels of this marker are lower in the blood, it means horses experience less muscle damage.
The natural vitamin E also resulted in lower TBARS (thiobarbituric acid-reactive substance) which suggests they had less oxidative damage. Horses on natural vitamin E also had improved stride duration compared to those on the synthetic form.
This study shows that Vitamin E, particularly in its natural form, helps equine athletes sustain high levels of activity by reducing oxidative damage and minimizing muscle damage. [1]
In another study, horses used for police service in Brazil were fed 2.8 mg selenium and 2,000 IU vitamin E (doses for a 400 kg horse). Their response to exercise was assessed before and after 30 days of supplementation.
After supplementation, horses were better adapted to exercise because they had less of the stress hormone cortisol. They also had improved energy metabolism as indicated by less lactic acid in the blood. [4]
Enhanced Immune Function
A study involving older horses ranging from 7 to 26 years old found that natural Vitamin E had an immune enhancing effect.
In the study, horses in the treatment group were fed natural vitamin E (alpha-tocopheryl acetate) for 16 weeks at a dose of 15 IU/kg of bodyweight. This is equivalent to a dose of 7500 IU for a 500 kg horse. Compared to horses in a placebo group not receiving any treatment, those horses given Vitamin E experienced improved immune function.
Specifically, the study showed that horses given vitamin E produced more antibodies after vaccination against West Nile virus. In addition, the ability for their immune cells to fight off bacteria was enhanced. [2]
Vitamin E supplementation to improve immune function is especially beneficial to older animals because immune function naturally declines with age.
Vitamin E Requirement in Horses
The National Research Council (NRC 2007) recommends a minimum daily intake of 1-2 IU per kg body weight. For a 500kg horse at maintenance the daily intake should be 500 to 1000 IU. This is easily met if horses have frequent access to fresh grasses and forages in pasture. Grazing on pasture provides approximately 2,000 IU per day. [5]
The vitamin E requirement increases to a minimum of 1000 IU per day in working horses and pregnant or lactating broodmares. Weanlings and yearlings require 500-750 IU Vitamin E per day.
It is important to note that NRC levels are not necessarily reflective of optimal Vitamin E intake and are merely the minimum required to prevent a deficiency. In many cases, feeding higher amounts of this vitamin can improve health and well-being.
The body condition of your horse might also determine how much vitamin E to provide. Skinny horses have less fat tissue to store vitamin E so they will require more in their diet, around 1500-2000 IU per day.
Higher levels can also be provided to horses with allergies, metabolic syndrome, that are frequently ill or recovering from illness. Daily doses up to 10,000 IU have been shown to be safe in horses.
Horses on pasture during the summer can build up stores of vitamin E in their liver, muscle and adipose (fat) tissue that they can use during winter months when they no longer have access to fresh grass or forages. However, this may not be sufficient to meet their daily requirement and optimize health.
Vitamin E Sources
Consult with an equine nutritionist to determine whether your horse needs additional Vitamin E in their diet. You can check your horse’s diet online using our diet analysis tool and our equine nutritionist will be happy to provide you with feed.
If you determine that your horse needs more Vitamin E, you can increase dietary consumption by allowing more access to lush pasture.
Keep in mind that fresh pasture might have high sugar content which could be a concern for overweight or insulin resistant horses. Magnesium levels of grasses in springtime and laminitis should also be taken into account.
To minimize loss of vitamin E from hay, cut it early in the season and store it in a dry, dark place. Sunlight and moisture are the main factors that contribute to vitamin E degradation from feed. In one study, alfalfa hay lost 50% of its vitamin E content over one month of storage. Also, earlier cuts of alfalfa hay have higher levels of vitamin E than later ones. [3]
Absorption of vitamin E is enhanced by fat in the diet. If you are interested in feeding supplemental vitamin E you may want to consider Mad Barn’s W-3 oil which is enriched with Vitamin E. A daily dose of 100 mL W-3 oil provides 1500 IU natural vitamin E. Daily total fat intake should not exceed 8% for equine diets.
Like all fat-soluble vitamins, excess vitamin E is stored in the body, mainly in the liver and in fat tissue. Toxicity can occur with overfeeding vitamin E; however, this is unlikely in horses.
High vitamin E intake can interfere with absorption of vitamin A. The fat content of the diet can also influence vitamin E absorption.
As with all vitamins and minerals, it is important to consider the whole diet to ensure there are no imbalances that can affect the absorption or function of vitamins and minerals. Submit your diet for analysis online and our equine nutritionist can help you review any potential changes to your feeding program.
Natural vs Synthetic Vitamin E
Although there are eight forms of vitamin E, most supplements for humans and animals contain alpha-tocopherol. When supplementing this vitamin, it is important to choose natural forms because it can be used much more readily by the horse’s tissues.
Natural forms are typically listed with a “d” prefix, like d-alpha-tocopherol, d-alpha tocopheryl acetate or d-alpha tocopheryl succinate. Synthetic vitamin E supplements will have “dl” as the prefix, such as dl-alpha tocopherol.
Absorption of natural and synthetic vitamin E is the same. However, the ability for tissues to use vitamin E is much greater with natural vitamin E than synthetic.
Mad Barn’s Natural E/Organic Se and Vitamin E supplements as well as AminoTrace+ all contain natural forms of vitamin E d-alpha-tocopherol.
Vitamin E Deficiency in Horses
In horses, Vitamin E and selenium deficiency often occur together and show similar signs. Suspected deficiency should be confirmed by a veterinarian.
Some non-specific signs that might suggest a vitamin E deficiency are:
- Muscle soreness or frequent tying-up after exercise
- Slow recovery from illness
- More time spent lying down
To determine whether your horse is deficient in vitamin E, a blood test can be done that measures the serum concentration of alpha-tocopherol. The following is the range of results: [3]
- Adequate: 2 ug/ml
- Marginal: 1.5-2 ug/ml
- Deficient: 1.5 ug/ml
Not all horses that have low levels of vitamin E in their blood will show outward signs of deficiency. Factors like breed and age can affect levels in serum without necessarily impacting health.
For example, within the adequate range (>2ug/ml) Thoroughbreds have been reported to have lower levels than other breeds (Quarter horses, Arabians, Percherons, Paints, Appaloosa). [3]
It is normal for foals, weanlings and yearlings to have lower levels than adult horses, but foals should be monitored for neurological conditions that may develop due to deficiency.
Severe Deficiency and Neurological Disorders
Horses with access to fresh pasture are unlikely to experience vitamin E deficiency. Long-term feeding of hay without supplemental vitamin E can result in severe deficiency in foals and adult horses.
Equine Motor Neuron Disease (EMND)
This is a neurodegenerative disorder in which myelin around the axons of nerves is lost, affecting their ability to send signals around the body.
Adult horses can develop EMND if exposed to vitamin E deficient diets for at least 18 months.
Signs of EMND:
- Loss of muscle mass all over the body (general muscle wasting)
- Standing with fore and hindlimbs close together
- Muscle twitching
- Uneasy standing – shifting weight between hind legs
- Carrying their head low
- Laying down for long periods of time
Unfortunately, this condition is difficult to resolve. Treatment with 5,000-7,000 IU alpha-tocopherol daily can improve or stabilize 80% of cases by 3 months, but half those animals are likely to remain disfigured. Unfortunately, 20% of cases continue to worsen even with high doses of vitamin E.[3]
White muscle disease (nutritional myodegeneration) is primarily due to selenium deficiency. However, low vitamin E can also contribute.
Signs of White Muscle Disease/Nutritional Myodegeneration:
- Weak muscles (difficulty getting up, trembling limbs, unable to stand)
- Stiff and firm painful muscles
- Difficulty breathing, pneumonia, foamy nasal discharge
- Rapid heart rate
- Sudden death
These conditions should be assessed by a veterinarian. Early intervention with vitamin E or selenium is crucial to minimizing long-term deficiencies.
Vitamin E Deficiency in Foals
Foals are especially susceptible to vitamin E deficiency because this vitamin is not passed through the placenta during pregnancy.
Foals can get vitamin E from their mother’s milk. However, if foals and their dams are raised without access to pasture, their blood vitamin E and selenium levels will drop over the first year of life. In this case, foals and dams should receive supplemental vitamin E particularly in the first year of life.
Equine Neuroaxonal Dystrophy (eNAD) or Equine Degenerative Myeloencephalopathy (EDM) is a neurological disorder that develops in foals that are genetically susceptible to this condition and are maintained on a low vitamin E diet.
Clinical signs are most likely to appear in foals between 6 and 12 months of age but can take up to 3 years of age.
Some clinical signs of eNAD/EDM are:
- Abnormal stride/gait – these foals might have difficulty positioning their legs and feet while walking. This might include dragging their feet, crossing their legs, a high stepping gait or an otherwise abnormal gait.
- Obtundation – decreased responsiveness or alertness. These foals might less responsive than normal to new sounds, people entering the stable etc.
- Decreased or absent menace response – this is a test of whether they flinch their eyes closed when something moves quickly towards their eyes.
This condition should be assessed by a veterinarian. Mares that are known carriers of eNAD/EDM genetic variants should receive supplemental vitamin E in late pregnancy to have higher levels in colostrum which might protect foals from developing the clinical signs of eNAD/EDM [5]
Vitamin E Toxicity in Horses
Risk of toxicity or complications from high-dose vitamin E supplementation is considered low in horses.
According to the NRC, the upper safe diet concentration is 20 IU / kg of body weight. For a 500kg horse the upper limit is 10,000 IU.
Above this level some issues might arise including problems with blood clotting and bone mineralization. Vitamin E supplementation at 10,000 IU or higher might interfere with vitamin A absorption.
High-dose vitamin E supplementation should be done on the advice of a veterinarian or equine nutritionist.
Mineral and vitamin levels in your horse’s diet should be adjusted in consultation with a qualified equine nutritionist. You can submit your horse’s diet for analysis online and one of our nutritionists will be happy to provide a complementary evaluation.
References
- Fagan, MM et al. Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses. Journal of Equine Vet Med. 2020.
- Petersson K H et al. The Influence of Vitamin E on Immune Function and Response to Vaccination in Older Horses. J Anim Sci. 2010.
- Finno, CJ and Valberg,SJ A Comparative Review of Vitamin E and Associated Equine
Disorders. J Vet Intern Med. 2012. - da Fonseca, LA et al.Influence of selenium and vitamin E supplementation on energy
metabolism in horses used in policing activity.Comp Clin Pathol. 2016. - Finno, CJ et al.Blood and Cerebrospinal Fluid a-Tocopherol and Selenium
Concentrations in Neonatal Foals with Neuroaxonal Dystrophy.J Vet Intern Med. 2015.
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