VITAMIN E
Vitamin E is a nutritional subject that has been receiving allot of attention from horse owners. Many owners are concerned about the levels of Vitamin E within their horse’s diet and whether supplementation is needed. Many of these concerns arise from owners because they realize Vitamin E is an important fat-soluble vitamin, however; many do not understand the facts about Vitamin E.
Vitamin E is a fat soluble vitamin that differs from the other fat soluble Vitamins A, D, and K because it is stored within the body for only a few weeks, and is also found to be nontoxic in horses. Vitamin E levels higher than 1,000 IU is not recommended due to interactions with Vitamin K. Vitamin E functions as an antioxidant. Vitamin E’s function within the horse’s body is protection of cells and tissues through its antioxidant properties. Vitamin E is located within the lipid bi-layer of cell membranes and tissues. It functions within cell membranes and tissues by capturing free oxygen radicals that would otherwise damage cells and tissues, hence Vitamin E is an antioxidant.
Vitamin E is known as a tocopherol on many ingredient labels. There are eight forms of tocopherols or Vitamin E. The only tocopherol that is naturally occurring and biologically 100% active is d-alpha tocopherol. One hundred percent biologically active indicates that d-alpha tocopherol is the form that not only occurs naturally within hay and feeds, but is also present within the horse’s body. Naturally occurring Vitamin E is highly unstable within feed stuffs, which has led to the production of synthetic Vitamin E. The two synthetically occurring forms are d (R,R,R) alpha tocopherol acetate and d,1 (all-rac) alpha tocopherol. These synthetic forms contain ester linkages to acetate which cannot function as antioxidants within feed stuffs until the ester linkage is broken by enzymes known as esterases within the horse’s digestive tract.
The types of forage that are high in d-tocopherol are green pastures and fresh cut hay. Thirty to eighty percent of d-tocopherol is lost between cutting and baling of hay. Grass hay contains 30 to 80 IU/kg d-tocopherol, while alfalfa hay contains 80 to 120 IU/kg d-tocopherol. Cereal grains contain 10 to 30 IU/kg and growing forage contains 100 to 450 IU/kg of naturally occurring Vitamin E. The National Research Council recommends 50 to 80 IU/kg of diet DM/day for foals, pregnant and lactating mares as well as working horses. As indicated, if you are feeding stored hay or grain that contains only the naturally occurring form of Vitamin E, supplementation of Vitamin E may be necessary especially during the winter months.
Supplementation is recommended because d-tocopherol is damaged during feed processing. Processing procedures such as heating, grinding, storage, dampness, and pelleting destroys naturally occurring Vitamin E. Grinding disrupts the internal structure of the seed and exposes unsaturated lipids to the air, leading to peroxidation of Vitamin E. Grains that are high in fat and contain a high amount of polyunsaturated fatty acids (PUFA) run an increased risk of becoming rancid. Rancidity of grains destroys natural occurring d-tocopherol leading to an increased need for supplementation.
Vitamin E is needed within your horse’s diet, especially if your horses are not allowed access to green pasture. If your horse’s diet contains the recommended levels of Vitamin E occurring predominately in the synthetic form, and your grain is not stored in hot, humid conditions for long periods of time, then supplementation is not recommended.
