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Vitamin E is a relatively common deficiency in our equine patients. It is present in fresh grass but is degraded quickly in dried hay. A simple blood test can help diagnose a deficiency, but the question then becomes – what is the best way to supplement?
To review some basics, vitamin E is a “fat soluble” vitamin (meaning it is stored in fat) and is necessary for neuromuscular function. It’s scientific name is Alpha-tocopherol. A low serum level will mean that the fat stores in the body have been depleted, which takes some time. Lack of vitamin E can lead to muscle disorders and sometimes neurologic disorders.

Vitamin E can be supplemented with a synthetic form or a natural form. The natural form is more bioavailable, however the synthetic form is still fairly common. In fact, most commercially available horse feeds contain synthetic vitamin E. While this seems like it should be sufficient for most horses, it actually is not.
Synthetic vitamin E is so poorly absorbed that it is not even recommended for use as a supplement by veterinarians. Some supplements will not state whether or not their vitamin E is natural, but there are some ways to tell. First off, if they do not state it’s natural, it’s probably synthetic! It can also be listed as dl-alpha-tocopherol (natural is d-alpha-tocopherol) or all-rac-alpha-tocopherol. Using a synthetic form may not help improve your horse’s deficiencies.

So now we know that we need to use a natural formulation, but which is better – powder or liquid? Studies have shown that when supplemented with the liquid form, serum vitamin E levels increase within 24 hours. Additionally, it was noted that there was a significant effect on CSF (cerebro-spinal fluid) levels of vitamin E with the liquid form. When using the powder form, it takes about 8-10 weeks to increase serum vitamin E levels to appropriate levels. Additionally, no significant effect was noted on CSF levels. So what does this mean?
Natural vitamin E in liquid form is quite expensive, however it is highly bioavailable. The powder form is cheaper but is less is absorbed. What is typically the most beneficial to the horse and easiest on your wallet, is to begin treatment with the liquid form for a minimum of 2 weeks then slowly transition to the powder form. This will increase the vitamin E levels quickly and help improve fat stores, then you can maintain levels using the powder formulation.
Keep in mind that for optimum supplementation, serum levels should be monitored throughout the year, or at least yearly. Additionally, not all horses will respond to supplementation as there may be other issues at play.