Vitamin E and selenium supplements abound and for good reason. Severe deficiencies can cause life-threatening muscle and nervous-system diseases. But these nutrients do far more in the horse’s body than protect muscles.
As critical antioxidants, they protect the immune-system cells from suffering ”friendly fire” damage as they go about their work, especially areas that have a high reliance on oxygen-fueled metabolism, like in the heart, muscle and brain. They also protect the red blood cells from damage during exercise. Even reproduction can be negatively affected by the inadequate intake of vitamin E and selenium, and these nutrients are an important part of detoxification systems.
All vitamins and minerals identified as ”essential” have critical roles to play, but what makes vitamin E and selenium particularly important is how likely deficiencies are.
The selenium level in feeds is a function primarily of soil levels. With the exception of a band of states through the lower two-thirds of the middle of the country, most areas are moderately to severely deficient in selenium.
Vitamin E is abundant in fresh grass, but most of it is destroyed by curing and baling, with the small amount remaining also rapidly destroyed during storage. Intact seeds and grains have some vitamin E, but not enough to fulfill requirements and this, too, declines with storage or any break in the integrity of the grain or seed.
Adding vitamin E to packaged feeds or multi-ingredient vitamin/mineral mixes is routinely done at low levels. Higher supplementation probably wouldn’t help much anyway because E is fragile, and its activity is readily destroyed by exposure to low-level bacterial or fungal activity, air, sunlight and the presence of free minerals. The solution is to meet the horse’s requirements by a separate supplement.
How Much Vitamin E'
While most of the recommended feeding levels for other nutrients are based more on flat-out deficiency-disease standards the level that actually can cause a deficiency disease vitamin E is an exception. Even the 1989 National Research Council (NRC) recommendations for feeding horses focuses more heavily on feeding adequate vitamin E to help avoid exercise-related muscle damage and pain, and to support good immune response to vaccines. Because maintaining optimal health is a more complicated process than inducing a full-blown deficiency disease, the numbers really haven’t been strictly formalized yet, and may never be, but present thinking is:
• Healthy adult horses, with no stress from disease, injury, infection or exercise, not reproductively active: bare minimum 800 to 1000 IU/day vitamin E.
• Healthy horses in regular exercise: 1800 to 3000 IU/day.
• Correction of vitamin E deficiency, or supplementation during diseases where higher requirements are likely such as chronic infections, nervous system diseases, muscular disorders, chronic lung disease like heaves 3000 to 5000 IU/day.
If you follow discussions on human supplements, you’ve likely seen arguments over what form of vitamin E is best. Water-soluble vitamin E is E that has been suspended in tiny droplets of fat. It doesn’t really dissolve, but it does remain in suspension inside the intestine and is immediately ready for absorption. Mixed tocopherol vitamin E are supplements that contain many or all of the different forms of vitamin E found naturally in plants. ”All natural” E is E in the form of all d-alpha-tocopherol, while ”synethetic” is a mixture of d and l forms.
Which is best'
A Kentucky Equine Research study showed blood levels of vitamin E are twice as high following supplementation with water-soluble E than with natural or synthetic vitamin E. However, studies have also shown that single blood draw levels may not correlate well with tissue levels, and that animals on identical diets can show variations as high as 150 to 200%, making it difficult to say with certainty the differences are significant.
Mixed tocopherols are a little easier to sort through. The only form of vitamin E found in the horse’s tissues is the alpha-tocopherol. The other forms may be converted to alpha, probably by intestinal organisms, but the one the body needs and wants is alpha. Note: An advantage to the synthetic d,l-alpha-tocopherol is that this form is more stable and slower to degrade over time than the other forms.
Natural versus synthetic vitamin E also creates a lot of argument related to the catch word natural, but the bottom line is that natural vitamin E is about 36% more bioavailable than synthetic. So as far as forms of vitamin E goes, you should remember that:
• The NRC recommendations are based on the synthetic, d,l-alpha-tocopherol form.
• If you’re using natural vitamin E, for every 1000 IU of requirement, substitute 750 IU of natural E.
• If you’re using water-soluble vitamin E, it may take only 500 IU to get the same benefit as 1000 IU of a synthetic.
• There’s no strong advantage to supplements with mixed tocopherols; the horse’s body wants alpha-tocopherol.
Toxicity isn’t a concern with vitamin E in any of the dosages we’ve mentioned. In fact, vitamin E toxicity has never been observed in horses. Although this vitamin is fat-soluble and found in the highest concentration in body fat, it isn’t stored at the same high levels as the other fat-soluble vitamins A and D, which can reach toxic levels.
Depletion studies have found that it’s easy to rapidly induce drops in vitamin E by feeding diets low in E. This may be a difference between how vitamins A and D are stored compared to vitamin E or may reflect the horse’s high requirements for E compared to what they get in the diet.
How Much Selenium'
Most people are cautious about feeding selenium, and many aren’t aware that selenium deficiency is widespread and poses potential problems for their horse. Like any nutrient, selenium in excess can be toxic. However, the safety margin for feeding selenium is wider than for vitamin A.
The estimated minimum requirement for a 1,000-lb. horse is 1 mg/day. The proposed upper safe limit of intake for long-term use is 20 mg/day. Even if your horse is eating hay and grain from a selenium-adequate area, with a level in the feed and hay of as high as 0.5 ppm, 22 lbs./day of this diet (10 kg.) would provide him with only 5 mg of selenium, which is plenty but still leaves a very wide safety margin of 15 mg/day.
If you’re still nervous about selenium, you don’t have to guess. Your local agricultural extension agent can give you details on soil and feed/forage selenium levels in your area. If you have a stable pasture or source of hay, selenium assays can be done on these. Another approach is simply to test the horse himself. Whole blood selenium assays are generally believed to be the most accurate. You can base your decision on whether to supplement or not on those results.
If you don’t do any testing, guarantee supplemental intake of at least 1 mg/day for inactive horses, 2 to 4 mg/day for exercising horses. There’s no solid evidence in any species that exercise increases selenium requirements. However, many factors can influence selenium absorption (such as the levels of other trace minerals in the diet), and the exercising horse has a more critical need for this important antioxidant. As above, unless your horse is eating a diet with an extremely high baseline level of selenium, this level of supplemental intake (1 to 4 mg/day) is safe.
The only form of selenium currently approved for use in horses in sodium selenite. Organic forms of selenium such as selenium yeast or the chelate selenomethionine have been shown in many species to be better absorbed. This may be true in the horse as well, but horse-specific information simply isn’t available.
As even a quick glance through the supplements shows, E-Se combination supplements come in a variety of dosing packages for both vitamin E and selenium (Se). The best product depends on your needs.
First, determine your horse’s current selenium intake (see sidebar). It’s safest to assume that your base diet provides little vitamin E if you’re not supplementing it, so begin by looking for a product that provides around 1000 IU of vitamin E if your horse is not in work, at least 2000 IU of vitamin E if working.
If you don’t need any more selenium, use a product that contains only vitamin E. In addition to the synthetic E supplements, you can now choose natural and water-soluble forms of E. Unless the horse has liver disease, or you know from blood tests your horse absorbs E poorly, we’d pass on the water-soluble E.
Even if you adjust the dose down to allow for as much as 100% better absorption, we don’t think the expense is warranted. Synthetic vitamin E isn’t quite as pricey as natural E, but again the higher price doesn’t warrant the small increase in bioavailability.
If you still want to go natural with your E source, Smart Pak E is a Best Buy. At 50??/day for 2500 IU of natural E, it’s a bit over twice as expensive as the best buys for synthetic E, with the added advantage of individual daily dose packs for the best possible preservation of potency.
The two best prices on synthetic E we found were Uckele’s Liquid E-50 and Animed’s Vitamin E Concentrate. The Uckele product is in an oil base, which eliminates the need to add oil to help absorption, and the oil also protects the E from exposure to air and moisture which will hasten the breakdown.
If you also need to add selenium, first locate the products that meet your selenium needs at the lowest dose then compare the vitamin E levels. We can’t give you a specific product recommendation here because it depends on your selenium requirement. That said, for highest potency of both E and Se at the best price it’s a photo finish between Uckele’s E + Se, Uckele’s E + Se 10X and Equerry’s Vitamin E and Selenium. All three provide a minimum of 2000 IU E and 2 mg Se at daily prices within pennies of each other.