During metabolic activity the body produces waste products that are highly reactive with the cells and in excess can damage the cell. They are called free radicals. Along with selenium (Se), vitamin E acts as an antioxidant and reduces free radical activity and the deleterious reactions of these waste products. Vitamin E helps maintain membrane integrity in virtually all cells of the body and deficiency is increasingly being recognized as a cause of neurological and muscle disease in horses.This article consists of information on vitamin E requirements, sources, and deficiency. Scientific reports and links to related articles including diseases of vitamin E deficiency are provided.

Vitamin E and selenium work together to reduce free radicals in the body. Therefore, selenium intake greatly affects the amount of vitamin E required in the diet and vice versa. As selenium concentrations in feeds varies remarkably around the world it is important to understand selenium's role in the diet of the horse: ...more.

Vitamin E can be expressed in either international units (IU) or mg. There is no universally accepted IU for vitamin E. In spite of that there is a well-accepted convention in the US, the USP IU and that we will use below. You can compare two different forms of vitaminE using their USP standard IUs. But if the product is expressed in milligrams you will need to do some conversion. To further complicate discussing vitamin E it comes in a number of man-made forms that have different activities per unit weight. You will see both natural and man-made products containing tocopherols, the alcohol form, and tocopheryls, the ester form. The alcohol forms are not stable and rapidly break down, therefore the ester forms are what is usually available. Here are the relative potencies of man made and natural form of vitamin E. Most man made products have a conversion of around 1, that is 1 mg equals about 1 IU. The natural products are about 40% more active that the man-made product.

• The man-made d,l-alpha-tocopheryl is the standard where 1 mg equals 1 IU.
• The natural form of vitamin E is d-alpha-tocopherol is more potent and 1 mg equal 1.46 IU.
• d,l-alpha-tocopherol 1 mg = 1.10 IU
• d-alpha-tocopheryl acetate 1 mg = 1.36 IU

NRC requirements for maintenance is 50 IU/ kg of feed. Pregnant, lactating mares, growing horses, and working horses an increase of 80 IU/kg was suggested because of reports that higher levels were needed to improve immune response and to maintain plasma vitamin E levels. It has been suggested that the requirement may even be higher and many recommend supplementing 1000 IU of vitamin E a day for all horses not on good pasture or not on maintenance rations. Vitamin E and vitamin A interactions have been reported in some species but no evidence of this has been found in the horse even with a 10-fold increase of dietary vitamin A.

Vitamin E resides in lipid membranes where it protects against exercise-induced muscle damage and improves immune response in horses. It is proposed that ascorbic acid spares tissue vitamin E by reducing the tocopheroxyl radical and restores the radical scavenging ability of vitamin E. Using mature exercising polo ponies, researchers in Connecticut studied the influence of dietary vitamin E (240 IU vitamin E/kg intake) and vitamin C (10 g ascorbic acid/day) on nutritional oxidative status. Serum ascorbate and tocopherol concentrations were higher in the vitamin E- and C-supplemented animals, especially in the late season. The authors concluded that the performance and welfare of the heavily worked animal such as the polo horse might be improved with vitamin E and C additions, especially late in the season when overtraining is an issue.

Feeding a concentrate with 160 versus 80 IU of dietary vitamin E/kg for 4 wk. before foaling and 4 wk. after foaling enhanced colostrum and improved blood levels of E in mares and foals. Concentrations of IgG, IgM, and IgA in colostrum were significantly enhanced by dietary vitamin E over control animals, presumably improving passive transfer and foal health.