Question

How long can I give my horse 10,000 IU of vitamin E daily?

Answer

Large amounts of vitamin E are oftentimes recommended for horses experiencing certain problems, including equine protozoal myeloencephalitis (EPM) and other neurological problems like equine motor neuron disease (EMND) and equine degenerative myeloencephalopathy (EDM). Without knowing why your horse was placed on this amount of vitamin E, I cannot give a detailed response and will therefore speak generally.

Nutrient Requirements of Horses, produced by the National Research Council, states that relatively high intakes of vitamin E do not appear to be toxic to horses; however, an upper safe limit is noted at 1,000 IU/kg dry matter fed in other species. That amount would be 10,000 IU per day for a 1,100-lb (500-kg) horse consuming 22 lb (10 kg) of forage and concentrate per day.

Although large amounts of vitamin E have not been shown to cause problems, it is probably not necessary, depending upon the specific product. When supplementing with a synthetic form of vitamin E (dl-alpha-tocopherol), more international units (IU) of vitamin E will be needed to ensure it is available to the horse. Natural-source vitamin E (d-alpha-tocopherol) is five times more bioavailable than synthetic forms. The natural-source vitamin E product Nano-E features nanodispersion technology, making it highly bioavailable and effective at raising vitamin E serum levels.

I recommend cutting back 500 IU daily until you are feeding 8,000 IU a day. If you don’t notice a big difference, you should be able to further decrease to 5,000 IU a few weeks later. For a horse in need of vitamin E supplementation, 5,000 IU is considered a high dose but more economical to maintain long-term.

I wish I could give a more thorough answer, but without access to detailed information about the horse and the reason for vitamin E supplementation, this is the best I can do. Be sure to discuss changes in vitamin E supplementation with your veterinarian before implementation.