Q: Most of the horse owners I board with supplement vitamin E to their horses. My horse receives a ration balancer daily, but I am now considering adding a vitamin E supplement. Is additional vitamin E required? Also, can I oversupplement vitamin E?

A: Vitamin E is an important nutrient for horses. It is an antioxidant that protects the muscle membranes from free-radical damage and supports muscle mass maintenance. A vitamin E deficiency in horses is associated with numerous muscle disorders, including equine motor neuron disease, equine neuroaxonal dystrophy/degenerative myeloencephalopathy, and vitamin E responsive myopathy.

Horses living on well-maintained pasture for at least six months of the year can naturally maintain their necessary vitamin E concentrations; however, many regions do not have this type of situation.

Vitamin E in Your Horse’s Ration Balancer

Feeding a ration balancer is a great place to start. When you feed your horse a balancer at the manufacturer’s recommended rate, it will meet his baseline vitamin E intake needs. However, note that concentrates typically contain synthetic vitamin E, which is not as bioavailable to the horse as the natural form present in pasture.

Testing Your Horse’s Vitamin E Levels

Prior to adding a vitamin E supplement, have your horse’s whole-body vitamin E checked.  Veterinarians do this by measuring blood concentrations, which will help them determine if your horse needs more vitamin E. If your horse has normal concentrations (> 2 micrograms per milliliter is the reference range for most laboratories), he likely does not need supplementation. Work with your veterinarian to determine the ideal levels for your individual horse (some horses might need more than the normal concentration levels depending on their health status).

Vitamin E Supplements for Your Horse

When choosing a supplement for your horse, opt for a natural source of vitamin E, which will be listed in the ingredients as natural vitamin E, RRR-alpha-tocopherol, or d-alpha-tocopherol. If your horse has a deficiency, the gold standard is to use a liquid (water dispersible) product because it has a higher biopotency (ability to function in the body).

The amount to supplement depends on what the horse already receives in his horse’s diet, along with what the blood results showed. The general recommendation is to provide 6 international units per kilogram (IU/kg) of body weight (BW) of liquid vitamin E if your horse is deficient but not showing clinical signs of any neuromuscular disease. If you use a powdered natural vitamin E product, the recommendation changes to 10 IU/kg BW/day. Plan to have your veterinarian recheck your horse’s vitamin E levels in two to three months so you can accurately adjust the dose.

Veterinarians and equine nutritionists do not recommend adding a vitamin E supplement to your horse’s ration without testing his current levels. Although researchers have yet to  study this in horses, they know high doses of vitamin E in humans interfere with vitamin K metabolism and can prevent blood clotting.

Take-Home Message

Vitamin E helps protect your horse’s muscles and nervous system, but not every horse needs supplementation. Before adding a vitamin E product, work with your veterinarian to test your horse’s vitamin E levels. The results can help determine whether supplementation is warranted and, if so, which product and dose to use.