Selenium (Se) is a trace mineral required in very small amounts in the equine diet. It’s a vital part of an antioxidant enzyme, glutathione peroxidase, which detoxifies cell-damaging peroxides. Vitamin E and Se neutralize harmful free radicals—Se “recharges” vitamin E’s antioxidant power, recycling it for more radical-scavenging power.

Additionally, Se is a component of an enzyme that helps produce the active form of the thyroid hormone that regulates metabolism.

Dietary Requirements of Se

Too little or too much Se can lead to serious health consequences, but there’s still some debate about the horse’s actual dietary requirement of Se. The National Research Council’s Nutrient Requirements of Horses (NRC 2007) recommends a minimum of 1-1.25 milligrams (mg) of Se per day for a 500-kilogram (kg) (1,100-pound) horse. To put that in perspective, a paper clip or a dollar bill each weigh approximately 1 gram, and 1 mg is 1/1000 of a gram!

Research suggests slightly more, about 2.5 mg of Se per day, might be beneficial for optimum immune function and prevention of