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.