Vitamin E is an essential nutrient, selenium is an essential mineral and both are antioxidants. Horses cannot produce either themselves so both must be present in their diets. They work in tandem playing important roles in a horse’s muscular function and immune response.
In very broad terms this is how they work in muscular function. When a horse is at work their muscles require huge amounts of energy to complete the tasks we ask of them. This requires the process of oxidation where fats, carbohydrates and proteins are converted into energy. But it also produces some unwanted byproducts called peroxides which are damaging to cell structure and function. As antioxidants, vitamin E reduces the formation of peroxides and selenium removes any peroxides that have been formed. If there is a lack of vitamin E, more peroxides are formed. Then more selenium is needed to remove them and vice-versa.
Having optimal levels of both reduces a horse’s risk of exercise induced muscular damage and aids peak performance.
For horses in hard work a deficiency in vitamin E and selenium can seriously hamper results with them becoming more prone to muscle damage, stiffness and a lack of endurance.
Horses susceptible to tying up are particularly vulnerable, supplementation of vitamin E and selenium has been used to aid them for many years. Commercial feed companies add them to their products because of this known link, so it’s worth working out how much they are already getting from their diet before supplementing. There are some calculations to help you work out how much of both your horse is currently getting below.
Horses deficient in vitamin E and selenium can also suffer with a lower immune response making them more susceptible to coughs and colds. As we know, when horses are housed in close proximity in training establishments, a few feeling under the weather can soon escalate to half the yard coughing!
Recently a possible link between selenium deficiency and cribbing has been discovered. Looking for a link between oxidative stress and cribbing, researchers investigated the possibility that a selenium deficiency could cause the behaviour. They tested selenium serum levels whilst at rest and whilst cribbing. They found that cribbers had a significantly lower selenium level than the control group. Selenium levels were also found to be at their lowest whilst they were cribbing. Other variables were also studied, but selenium levels were the only marker that was significantly different between the control and cribbing groups, pointing to a direct link between low selenium levels and cribbing behaviour.
The National Research Council’s requirement for a 500kg horse at rest is 500 iu (International Units) per day, whilst they recommend 1,000 iu per day for horses in hard work. Many researchers believe this is under-estimating the needs of those in hard work and is not enough to maintain levels of vitamin E in the muscle during training. They believe that 1,500 – 2,500 iu per day is needed to sustain correct levels during prolonged regular exercise.
It has been reported that an even higher intake of up to 5,000 iu per day has been shown to reduce the rise in CK (Creatine Kinase) levels during exercise. If you have ever had a horse tie up you might have heard your vet talk about CK levels. CK is a protein released into the bloodstream, along with AST (Aspartate Transaminase), when muscle cells have been damaged during exercise. Vets will use levels of these two proteins when assessing if and how badly a horse has tied up.
In general, horses who have access to good quality green pasture for long parts of the day will easily meet their needs for vitamin E. However, racehorses and competition horses in full training are unlikely to be out at grass enough to get an adequate intake. This lack is further compounded by the fact that the levels of vitamin E in forage such as hay drop substantially during the making and storage of it. Between 30-80% of the vitamin E is lost between cutting and baling alone. Grass and soil quality also plays a part in selenium deficiencies too.
A 500kg horse requires 2-3mg per day of selenium for optimal immune function. A factor to consider is that selenium deficiency in UK soils is widespread and severe in some areas, local data can be found online. Deficiency in the soil means that grass and in turn hay and other forage will be lacking in the mineral too. If your horse is not getting enough selenium from its forage then it will need to be present in their food.
You can get your hay or haylage tested by all major feed companies and find out what levels of vitamin E and selenium are present.
To work out how much your horse is getting from its diet take a look at feed bags and supplement tubs or feed company websites for nutritional information. They will show how much selenium and vitamin E is included per kg.
Weigh out how much food your horse is getting daily. As a rough guide, a regular scoop of nuts is around 2kg whilst mix is around 1.5kg.
For example, if your feed contains 0.5mg selenium per kg and your horse is getting 4kg of food then they are getting 2mg daily. For supplements, they often give you the nutritional values per each miniature scoop, if not get your calculator out!
If your tiny scoop is 25g and your feed states 1mg per kg
1kg = 1,000g
1,000 ÷ 25 = 40
1 ÷ 40 = 0.025
Each 25g scoop is 0.025mg of selenium
Vitamin E is not toxic and therefore high levels are not harmful. Selenium can reach toxic levels above around 6mg per day but you would have to feed many times over the suggested dosage of any selenium supplement to reach these levels. The only real danger would be a horse finding its way into a feed store and getting access to an open tub of selenium supplement.
Organic Selenium offers greater bioavailability than synthetic versions and will have a slightly better absorption rate. Organic selenium often comes in the form of selenium enriched yeast. Sodium Selenite is the most common form of selenium found in feeds and supplements. Although organic selenium is absorbed slightly better, sodium selenite is absorbed perfectly efficiently.
Natural vitamin E supplements also offer greater bioavailability than their synthetic counterparts. However, unless your horse has a significantly harmful deficiency a more cost effective synthetic supplement will suffice.
There are many supplements that include both vitamin E and selenium because of how they work together in the equine body. They are also found in many broad spectrum health supplements.