The Importance of Vitamin E in Horse Health | Equine Science Matters™

Vitamin E is an important antioxidant that helps protect cells from damage and supports normal muscle and immune function. During exercise, the body produces more free radicals and other reactive compounds. Vitamin E helps the body manage these compounds and protect cells. 

However, oxidative stress is not necessarily a bad thing. A certain amount is a normal part of exercise and helps the body adapt to training. The aim is therefore not to eliminate oxidative stress, but to maintain a healthy balance. You can read more about exercise-induced muscle fatigue in horses here. 
 

How much vitamin E does a horse need? 

Vitamin E is an essential vitamin, meaning horses must obtain it from their diet. Requirements vary according to factors such as workload, life stage and diet. 

The National Research Council (NRC) gives the following daily recommendations: 

These figures refer to the total daily intake from the whole diet, including forage, hard feed and supplements. 

What about grass and hay? 

Fresh, actively growing grass can be an excellent source of vitamin E. However, levels can vary considerably depending on the maturity and quality of the grass and growing conditions. Drought, poor grass growth and mature pasture can all reduce the amount available. 

Vitamin E also declines during harvesting and storage, so hay generally provides less vitamin E than fresh pasture. This means that horses receiving a lot of conserved forage, or those grazing poor-quality pasture, may have a lower dietary intake. 

Vitamin E has a relatively wide safety margin, and horses can safely consume considerably more than the basic NRC requirement. There is also some evidence that the NRC levels may be sufficient, but are not necessarily optimal, particularly for those undertaking significant exercise or with specific nutritional needs. For horses in regular work, a modest increase above the NRC recommendation can therefore be appropriate. Horses with certain muscle or neurological conditions, such as Polysaccharide Storage Myopathy (PSSM), equine motor neuron disease (EMND) or equine degenerative myeloencephalopathy (EDM), may require substantially higher intakes under veterinary or nutritional guidance. 

Importantly, these amounts refer to the total diet. A horse grazing good-quality, growing pasture may obtain a significant amount of vitamin E naturally and therefore need less supplementation than a horse consuming mainly hay. 

Does the form of vitamin E matter? 

Yes. Vitamin E occurs in several forms, but alpha-tocopherol is the form most relevant to horses. 

Fortified feeds and supplements generally provide either: 

• RRR-alpha-tocopherol – the natural form  

• all-rac-alpha-tocopherol – the synthetic form  

Research in horses indicates that RRR-alpha-tocopherol is more readily absorbed and retained than synthetic forms, although the practical difference depends on the dose and the individual horse. 

When comparing supplements, it is therefore important to look at both the amount and form of vitamin E provided. 

Vitamin E and selenium 

Vitamin E is often combined with selenium, another essential nutrient involved in the body's antioxidant defence system. The two nutrients work together to help protect cells from oxidative damage. 

However, selenium is very different from vitamin E in two important respects:  

1. It has a much narrower safety margin. Too much selenium can be harmful, and providing more than the horse requires does not necessarily provide additional antioxidant benefit. 

2. Its levels in forage are determined by the amount in the soil as the grass is growing, and the levels do not drop in hay or haylage, as is the case with Vitamin E. 

Before adding a selenium-containing supplement, consider the total selenium supplied by forage, hard feed, balancers and existing supplements. If a horse is already receiving a fortified feed or balancer at the recommended feeding rate, its selenium intake may already be adequate. 

In these cases, supplementing vitamin E without additional selenium can be a useful way of increasing vitamin E intake without unnecessarily increasing selenium. 

The bottom line 

Vitamin E is an important nutrient for horses, particularly those in regular work or with increased nutritional requirements. Fresh, growing grass is a valuable source, but vitamin E levels can fall with poor growing conditions, grass maturity and hay storage. 

Where supplementation is indicated, the form of vitamin E matters, and natural RRR-alpha-tocopherol is generally more bioavailable than synthetic forms. 

Selenium should be treated separately: more is not necessarily better, and total dietary intake should be considered before supplementing. 

The best approach is to consider the horse's whole diet, including forage, hard feed and supplements. If you would like any help deciding whether supplementation could be beneficial for your horse and appropriate levels, please don’t hesitate to reach out to our nutrition team.