Are You Feeding Your Horse Enough Vitamin E?

consuming diets higher in unsaturated fat sources such as corn soybean or canola oil may have reduced efficiency in utilizing dietary vitamin E sources. This could potentially increase the vitamin E requirement for hardworking horses that are consuming high fat feed supplements.
Most commercially available complete equine mineral supplements provide vitamin E at a minimum of 500 IU for a mature 500 kg horse thereby providing supplemental vitamin E at NRC recommended maintenance levels. This intake will provide an adequate level of the vitamin for most pleasure horses. The expectation is undoubtedly that any additional vitamin E required will be provided by the forages the horse eats or additional complete feed sources.
Unfortunately a reality of modern horse ownership is that few of our horses especially those in significant training or work have much access to fresh forage like pasture. Even semisedentary pleasure horses are likely to be limited in their access to pasture as we understand so much more now about the impact it has on horses with metabolic issues. Few pleasure horse are allowed unlimited access to rapidly growing spring pasture because of concerns such as insulin resistance and laminitis. Its too bad because fresh pasture is probably one of the best sources of vitamin E available for your horse.
Stored forages such as hay have reasonable levels of vitamin E at harvest but the levels decline rapidly after that. Most equine nutritionists assume that stored forages of any kind contribute no vitamin E to an equine diet.
An assessment of your horses diet may well show that you are providing your horse with vitamin E at a level that is adequate for maintenance. If however you have a horse that is in hard work senior growing pregnant lactating or a breeding stallion its definitely worthwhile to consider supplementing hisher diet with additional vitamin E.
Can high levels of vitamin E be toxic? 
Vitamin E is essentially nontoxic and therapeutic doses in equine diets can be as high as 8000 IU per day. The NRC Equine Nutritional Guidelines suggest that a maximum safe intake of vitamin E for any horse should not exceed 1000 IUkg of dry matter intake. Assuming a daily dry matter intake of approximately two percent of body weight a safe upper limit for vitamin E for a 500 kg horse would be about 10000 IU
What about vitamin E deficiencies?
Several disease conditions have been linked to deficiencies in vitamin E.