Does your horse need a Vitamin E supplement added to his or her feeding program?
Hay is the most important component of a horse’s diet, and contributes almost all the necessary macronutrients (protein, fat and carbohydrates) and micronutrients (vitamins and minerals) that our horses need.
Notice how I said almost? Hay does not cover all our horses’ nutrient requirements and there is one micronutrient in particular that is often deficient in horses on a hay-based diet.
That essential nutrient is vitamin E.
What is Vitamin E?
Vitamin E is an antioxidant involved in immune response, metabolism, and cellular health.
It acts as an antioxidant to neutralize free radicals that are produced naturally during metabolism of sugars and fat into energy. These free radicals are volatile in nature and can cause damage to cell membranes, enzymes and other intracellular components.
Vitamin E deficiencies have been associated with neuromuscular conditions such as: 
- White muscle disease
- Neuraxonal dystrophy
- Pigment retinopathy
- Vitamin E deficiency myopathy
- Masseter muscle atrophy in adults
- Equine degenerative myeloencephalopathy
- Equine motor neuron disease
Some of these conditions, such as white muscle disease, are also associated with both selenium and vitamin E deficiency.
While these conditions are rare, in order to optimize our horse’s nutrition, we need to ensure they are getting enough vitamin E (and selenium) to support their overall health and wellbeing.
Vitamin E status
The best way to determine your horse’s vitamin E status is with a blood test.
Horses grazing good pasture, which is abundant in vitamin E, have serum levels of 3 to 6 ug / mL.  Therefore, blood vitamin E levels within this range would be considered adequate.
Horses that are not grazing are at risk of becoming vitamin E deficient because this nutrient is lost during hay storage. Indeed, blood tests have shown lower levels of vitamin E in horses on hay and alfalfa pellets (2.8 ug / mL), compared to horses on pasture (4.2 ug / mL). 
Types of Vitamin E
The term ‘Vitamin E’ describes a family of eight structures that can be divided into two groups – tocopherols and tocotrienols – depending on their structural formation.
Typically, in feed formulations, we most often see vitamin E in the form of alpha-tocopherol as this is the form preferred by the body.
Any of the tocopherols or tocotrienols may be absorbed in the gut but the liver preferentially packages and secretes alpha-tocopherol for the tissues.
Natural vs Synthetic Vitamin E
Equine dietary supplements will use natural and synthetic forms of alpha-tocopherol. The natural forms of Vitamin E are superior because they have higher biological activity. Natural and synthetic forms are absorbed equally well by the gut but the liver preferentially secretes natural vitamin E for the rest of the body to use. 
On a feed tag, natural forms of this vitamin will be listed with a “d” prefix, like d-alpha-tocopherol, d-alpha tocopheryl acetate or d-alpha tocopheryl succinate. If you see a “dl” prefix, this is a synthetic form of Vitamin E, such as dl-alpha tocopherol.
In feeds and supplements, alpha-tocopherol is typically bound to acetate or succinate forms for better stability and a longer shelf-life.