Horses require vitamin E in their diets for many biological functions. One of vitamin E’s most well-known roles is as a powerful antioxidant that promotes health of muscle and nerve cells. Because it is fat-soluble, vitamin E must be consumed with dietary fat in order to be properly absorbed in the body. Sources of vitamin E include fresh pasture, good-quality hay, and fortified concentrates.
Forms of Vitamin E
Not all vitamin E is the same. There are several forms, or isomers, of vitamin E, but only natural vitamin E contains a form known as d-alpha-tocopherol. A recent study suggested that natural vitamin E may be superior to synthetic versions in mitigating oxidative and muscle cell damage in exercising horses compared to the synthetic version*.
Numerous vitamin E supplements are available, but differences in their bioavailability have been noted by researchers. Natural vitamin E, or d-alpha-tocopherol, has been scientifically proven to be the most bioavailable form. Synthetic vitamin E, or dl-alpha-tocopherol, contains a mixture of several isomers of vitamin E, not all of which are readily absorbed, hence it is less bioavailable. Water-dispersible, natural d-alpha-tocopherol increased serum concentration of vitamin E within one week, compared to a powdered form that took seven weeks to reach a comparable concentration in horses with low vitamin E status**.
According to Nutrient Requirements of Horses (NRC, 2007), an 1100-lb (500-kg) horse in light to moderate exercise requires 800-900 IU of vitamin E per day.