27/03/2025
MYTH: Horses must eat natural vitamin E because they can’t use synthetic vitamin E.
FACT: The body is capable of absorbing both natural vitamin E and synthetic vitamin E. The difference is in how much must be fed to accomplish the same rate of absorption. Vitamin E is listed on the label in IU’s (international units) which is a measure of biological activity rather than quantity. For example, supplying 1 mg of vitamin E to the diet can be accomplished by adding either 1.49 IU of natural vitamin E or 2.22 IU of synthetic vitamin E, according to the National Institutes of Health.
Vitamin E serves as an antioxidant and maintains normal neuromuscular function. Lush green pasture typically provides adequate levels of vitamin E, however seasonal changes and the need to feed hay prevent the majority of horses from obtaining adequate amounts of vitamin E through forage alone. Therefore, vitamin E is often added to commercial horse feeds/supplements to balance the vitamin E deficiency. In some disease processes, natural vitamin E may be preferential to synthetic vitamin E simply because it is more easily absorbed. However, care should be taken not to over-dose vitamin E for long periods of time because it can reach toxic levels.
The National Research Council has established an upper safe limit of 10,000 IU per day for an 1100 lb horse. THIS LEVEL WAS BASED ON SYNTHETIC VITAMIN E, not natural, therefore if using only natural vitamin E, the upper limit should be 6,700 IU/day for the same horse. Always consult with an equine nutritionist about the best form of vitamin E for your horse’s situation. Supplying the diet with 500 IU/day of synthetic vitamin E is sufficient for most exercising horses. UC Davis School of Veterinary Medicine notes that long term supplementation above 10,000 IU could lead to coagulophathy, impaired bone mineralization, and may be detrimental to absorption of certain nutrients from the diet.
