Vitamin E (dl-alpha tocopherol) is most recognized as an antioxidant that works closely with Selenium and Vitamin C to protect the body from the oxidative stress of exercise, as well as support proper immune system function. Vitamin E is found in high amounts in fresh pasture, horses without access to pasture or are under stress or high activity should receive Vitamin E supplementation as part of standard diet.
Selenium is a trace mineral that along with vitamin E function in a partnership that helps to protect body tissues from
free radical damage that occurs during oxidation (the conversion of feedstuffs into energy). While some parts of the country have high levels
of selenium in their soil and therefore the plants that grow there, selenium deficiency has been reported in 46 states.
Therefore, most horses will need supplementation to meet the NRC requirement of 1 mg/day for maintenance. For optimum immune function and exercise recovery, 2 to 3 mg/day is recommended, which is still well below 50 mg/day which may be the upper safe limit.
Magnesium (Mg) is a vital macromineral, and it is becoming increasingly recommended by veterinarians for various treatments in the horse. Because one of the clinical signs of magnesium deficiency is nervousness, it
is added to many calming supplements. Magnesium helps support a normal inflammatory response. Magnesium may play a role in insulin resistance and equine metabolic syndrome. Within the muscle calcium
and magnesium work antagonistically — calcium causing muscle contraction and magnesium inducing relaxation. If there is not enough magnesium, muscles tend to spasm. Although the presence of low magnesium
in the muscle tissue may stem from a genetic disorder rather than dietary quantities, there are reports of horses that have responded to magnesium supplementation for support of chronic tying-up.