03/07/2026
Vitamin E in Horses: Why It Matters and How to Get It Right
Hunter Greer, DVM
Vitamin E is a critically important antioxidant that protects cells and tissues from damage, and thus, plays an important role in supporting the normal function of various body systems. Vitamin E is considered an essential nutrient, and it cannot be produced by the body to meet necessary requirements; instead, requirements must be met via dietary intake or supplementation. Fresh, green grass is a great source of natural vitamin E, but levels become insufficient once harvested as hay.
Access to green pasture is limited here in Central Oregon, especially during certain times of the year. Because of this, our horses are at risk of a deficiency that can be accompanied by severe potential health repercussions. There are several vitamin E-deficient diseases, most notably impacting the nervous system and muscles. Signs may include muscle wasting, weakness, low energy, prolonged recovery from exercise, performance issues, lack of coordination, abnormal stance, and behavioral changes. In many cases, an effective treatment or cure is lacking. Hence, prevention is the key.
Although individual animal factors and genetics play a role in the development of such diseases, vitamin E supplementation is necessary for many horses. Supplementation is not a one-size-fits-all scenario. Vitamin E requirements vary for each horse based on life stage, use, diet, and the environment. In addition, we now know that over-supplementation can have deleterious consequences at high levels. Measuring the vitamin E concentration in your horse’s blood is the most reliable way to determine their vitamin E status and will allow your veterinarian to tailor recommendations to your horse’s individual needs. Blood concentrations should be measured prior to starting supplementation and routinely monitored thereafter. For many horses, we make an annual blood test for vitamin E and selenium part of their annual wellness program.
Several supplements are available for over-the-counter use, but not all products are created equal. Alpha-tocopherol, the active form of Vitamin E, is the main ingredient in available supplements. However, it exists in synthetic (dl-alpha-tocopherol), natural (d-alpha-tocopherol), and natural water-soluble forms. While the synthetic form is cheaper than natural forms, it is absorbed from the gut less readily and, as a result, does not adequately increase blood and tissue concentrations of vitamin E. Therefore, it is less effective at addressing Vitamin E deficiencies. Conversely, natural water-soluble formulations have been shown to be most effective at rapidly increasing blood and tissue levels of vitamin E. As a horse owner, you should look for products containing the natural forms of Vitamin E, d-alpha-tocopherol or d-alpha tocopherol acetate, when considering the use of a supplement. Avoid use of d-l-alpha-tocopherol, which is the synthetic and poorly absorbed form.
Dosing recommendations largely depend on your horse’s individual needs, blood concentrations, presence or absence of clinical signs associated with a vitamin E deficiency, and the type of Vitamin E supplement (synthetic vs. natural vs. water dispersible; liquid vs. pelleted/powered). Ongoing modifications to the supplemental program are made based on repeat testing and individual responses. The National Research Council recommends 1-2 IU/kg body weight of daily vitamin E for horses; however, the form of vitamin E (synthetic vs. natural) is not accounted for in these recommendations which is an important thing to consider regarding appropriate dosing.
Consult with your veterinarian for recommendations on how to meet your horse’s Vitamin E requirements and for guidance on the dose and formulation used.
