Vitamin E is a powerful antioxidant vitamin that cannot be made by the horse and must be obtained from the diet. Vitamin E is essential for healthy functioning of muscles, the immune system, reproductive function, skin and the nervous system. Many horses may have an increased need for Vitamin E, including those on low Vitamin E intake due to low quality forage, those on diets with added oil, those in work, "older" animals and those used for breeding.