Vitamin E is one of the horse’s most important vitamins
Vitamin E is an important part of every horse’s diet. A horse cannot produce vitamin E itself—it must be obtained from the diet. A horse will get enough vitamin E if it grazes or receives fresh grass daily. Otherwise, and during the indoor feeding season, vitamin E supplementation is needed, because vitamin E does not keep well in dry hay. The form in which a horse receives vitamin E matters a great deal.
“Vitamin E” is a collective name for various tocopherol and tocotrienol compounds, which occur in alpha, beta, gamma, and delta forms. These forms differ in absorption, structure, and metabolism. The key differences between supplements are generally whether the vitamin E is natural or synthetic, and in what form it is provided. Natural vitamin E is RRR-alpha-tocopherol and d-alpha-tocopherol; synthetic vitamin E is dl-alpha-tocopherol. The natural form is the most biologically active and integrates into cell membranes to slow damage. Synthetic vitamin E is not as effective in the body as natural vitamin E. Studies have shown that the bioavailability of natural vitamin E is superior—at least 1.5 times that of synthetic vitamin E. Natural vitamin E is reliably utilized by the horse’s body.
The form of vitamin E
In addition to the difference between natural and synthetic, another important factor is the form vitamin E takes in the supplement. Vitamin E is sensitive and its stability can be problematic, so it is often converted into a so-called acetate form to improve shelf life. The acetate form must be converted in the intestine into a usable form before it can be absorbed. First, the ester must be removed from the acetate form, and then the body must make the acetate form water-soluble with the help of bile salts. For this reason, synthetic or acetate-form vitamin E must be given in larger amounts than natural, non-acetate vitamin E.¹ Natural vitamin E is transported by a specialized transport protein as well as by chylomicrons. This transport protein also carries synthetic vitamin E, but not as efficiently as it carries natural vitamin E.³ Vitamin E is also transported in red blood cell membranes.⁴ For these reasons, it is worth paying attention to what kind of vitamin E you buy—natural vitamin E that is not in acetate form is absorbed most efficiently.
Vitamin E has many important functions
Vitamin E acts as an antioxidant in the body, contributing to the health of cell membranes and protecting the horse’s body, intracellular compounds, and enzymes from the harmful effects of oxygen. Vitamin E also improves the absorption and storage of vitamin A and participates in DNA synthesis, immune function, and hormone production.⁵ By participating in DNA synthesis, vitamin E also plays an important role in reproduction.⁶ Vitamin E affects muscle tissue condition and energy production, and it increases resistance against equine influenza and tetanus. Vitamin E deficiency predisposes the horse to muscle damage and leads to reduced performance.⁷ Vitamin E deficiency in a competing horse or a horse under heavy physical strain may even lead to hindquarter paralysis. Excess vitamin E intake is not dangerous, and according to studies it is the safest of the fat-soluble vitamins. Vitamin E has been shown to be safe even at high doses, although at very high doses it may interfere with the function of other fat-soluble vitamins.
Vitamin E is found in fresh hay and silage. Grains and dried hay contain less vitamin E. During harvesting and storage, the vitamin E content in hay can decrease by as much as 80%.¹⁰ Oils added to the diet should also be taken into account in vitamin E feeding, because higher oil intake increases the horse’s vitamin E requirement. Vitamin E needs increase by about 200 mg per deciliter of oil. Vitamin E requirements also increase if the feed contains only small amounts of selenium. Selenium deficiency occurs in horses living in regions with selenium-poor soils. Such regions include, for example, Scandinavia and the British Isles.
Research references:
1 Turunen 2016
3 Waldridge 2017, 101
4 Aro et al. 2007, 151
5 Briggs 2007, 69
6 Cuddeford 2003, 51
7 Saastamoinen et al. 2007, 19
8 Saastamoinen et al., 2007, 19
9 NRC 2007, 114
10 Autio 2015
