Vitamin E for Hay Fed Horses

Known for its potent antioxidant capacity, vitamin E is a fat-soluble vitamin that is abundant in good quality pasture grass. As a result, horses grazing good quality pasture for many hours a day typically have serum vitamin E levels well over what is considered the normal range. Because vitamin E loves fat (lipophilic) it is easily incorporated into cell membranes which are composed of a fat bilayer. Here it protects unsaturated fats especially the polyunsaturated fats (for example omega-3 and 6 fats) and other at-risk compounds from oxidative damage. 

Vitamin E activity in foods is due to a group of compounds known as tocopherols and tocotrienols of which there are 8 forms. D-α-tocopherol has the widest distribution and greatest biologic activity; less active are β-tocopherol, γ-tocopherol, and α-tocotrienol. Equine vitamin E requirements are therefore based on α-tocopherol.  This is why in feeds and supplements that contain added vitamin E it is the α-tocopherol form that is used. 

Synthetic or All-Natural Vitamin E? All Natural is Best

However, α-tocopherol comes in two main forms, synthetic and all natural. The synthetic version dl-α-tocopherol is industrially derived from petroleum sources and the natural form d-α-tocopherol is derived from plant sources. The natural d-α-tocopherol form has been shown to be superior in that it has far greater biopotency than the synthetic dl-α-tocopherol. 

Sometimes there is confusion over the use of the international units (IU) used to measure vitamin E in horse products. The assumption is often that 1 IU of natural vitamin E is the same as 1 IU of synthetic. However, this is not the case as 1 IU of natural vitamin E is equivalent to 0.67 mg of α-tocopherol while1 IU of synthetic vitamin E has the same biopotency as only 0.45 mg α-tocopherol. This means that to get the same bioavailability of vitamin E using synthetic dl-α-tocopherol you would need to feed more IUs. 

Even when feeding a greater number of IU’s of the synthetic form it may not be enough. The transport proteins that take vitamin E around the body prefer the natural form. Additionally, the synthetic form is excreted from the body more rapidly. Therefore, if relying on synthetic vitamin E the horse’s tissues may not ever receive the amount necessary to avoid deficiency even when seemingly adequate amounts of vitamin E are being provided in the diet. 

In the natural diet, Vitamin E is found dissolved in dietary fat and is liberated and absorbed during fat digestion. In fact, unless micellized to make it water soluble, as a fat-soluble vitamin, vitamin E requires fat for absorption after it is consumed. This is one of the secrets to the success of the O3 Animal health line of products. The oil that provides the product’s foundation promotes the absorption of vitamin E. 

After emulsification of dietary fat by bile in the small intestine, the enzyme lipase breaks fats down into smaller particles. These mixtures of smaller fat particles, bile salts and lipase cluster together to create micelles. Caught up in these micelles is vitamin E. The micelles bump up against the border of the small intestine depositing their contents into the epithelial cells (the cells that make up the lining of the intestinal tract). From here they pass into the lymphatic system in carriers known as chylomicrons before being broken down and transported to the liver and peripheral tissues in the bloodstream.  Mixing vitamin E in oil helps to maximize the absorption of the vitamin E in the O3 Animal Health product line helping to facilitate absorption from the gut and transport to the liver. 

Vitamin E is Lacking in Hay

If the horse’s natural diet of pasture grass is so abundant in natural vitamin E, why does any of this matter? Because in reality very few horses have access to good quality pasture year-round and vitamin E levels in hay are very low. This is because vitamin E is not particularly heat stable and much is lost during the hay curing process. This means that horses relying on hay as their forage source are being fed diets potentially very low in vitamin E. 

Vitamin E in Commercial feeds are likely Synthetic

While commercial feeds often contain vitamin E, many feeds rely on synthetic forms with lower bioavailability. Additionally, other ingredients in the feed such as added trace minerals may negatively impact the amount of active vitamin E available for the horse. 

Low Vitamin E Level Negatively Affect Health of the Horse

Over time, unable to adequately fight off the impacts of cellular oxidative damage, vitamin E deficits can negatively impact the horse’s health and performance. This may take the form of poor exercise recovery, muscle soreness, depressed immune function, lowered reproductive success, and in severe cases neurologic conditions such as vitamin E muscle myopathy, and equine motor neurons disease. Vitamin E deficiency is a concern year-round in horses relying on hay for their forage and becomes a concern for pasture managed horses when pasture becomes sparse and quality drops.

Test for Horse for Vitamin Regularly

The best way to determine whether additional vitamin E supplementation is necessary is to have your veterinarian draw blood and test serum α-tocopherol levels. If deficient, levels can be brought up most quickly by utilizing water soluble micellized forms of vitamin E. however, the expense of these forms often make them unrealistic for long term use and horses can be successfully transitioned to more cost-effective forms of supplementation over time. With their naturally sourced α-tocopherol dispersed in oil for maximum absorption, our Equine Mega Basic, Equine Omega Complete and Equine Omega Vitamin E are excellent options for long term supplementation.