Vitamin E can be provided to horses in both natural and synthetic forms.

“Synthetic vitamin E is what we see added to many horse feeds and supplements because it is less expensive,” says Tania Cubitt, PhD, an equine nutritionist with Performance Horse Nutrition, a consulting firm in Middleburg, Virginia. “When you see synthetic vitamin E listed on a label, it will be ‘dl-alpha-tocopherol,’ or some variation starting with a ‘dl.’ Natural vitamin E will be listed as d-alpha-tocopherol or the tocotrienols, without the ‘l.’”

There are differences in how the horse’s body absorbs the two forms. “Specific transport proteins in the liver seem to bind better to the natural form, allowing it to be transported to other tissues,” says Cubitt. “Synthetic forms are excreted faster than the natural form, and they don’t have as much time to get into the tissues where they are needed.” In other words, the horse has to consume more of the synthetic form to achieve the same levels in the bloodstream as the natural form.

However, the natural form costs more. “The natural products are expensive—usually about twice that of a synthetic product, or more,” says Carey Williams, PhD, of Rutgers. “Your choice depends on what you want to do: If you want to feed twice as much of the synthetic product at the cheaper price, you will be getting about the same effect. You can feed less of the natural product or a little more of the synthetic product. In terms of cost, it would end up very similar.”

Other effects are also likely to be about the same, according to Williams. “There’s been a huge debate regarding whether to use the natural or the synthetic products. There are a lot of people who swear by one or the other. I’ve done research with both types, but most of my research has been with the synthetic product, and we got antioxidant benefits.”

With either form, absorption can be improved by adding fat to a horse’s ration. The fats bind with the vitamin E and help to carry it across the intestinal wall and into the bloodstream. Researchers have also explored other methods to improve the absorption. Some products contain “micellized vitamin E,” which means it has been chemically changed to improve absorption. Another approach is called nanodispersion, which separates the vitamin E into tiny droplets that disperse across a wider range of intestinal wall. Both of these methods have been shown to aid absorption.