Why Do Horses Need Selenium?

Healthy Horse Guard Horse

17 year old Quarter Horse

The Importance Selenium
has several roles in horse health, but the most well-known is as a key element in antioxidant defense, which makes it important in every cell in the body as well as in immune defense.

The body produces radical oxygen metabolites (ROM) as a normal consequence of oxygen metabolism. Selenium-requiring enzymes such as glutathione peroxidase (GSH-Px) neutralize ROM, rendering them harmless and protecting cellular machinery from damage.

Other basic processes requiring selenium for normal function include growth, disease defense and reproduction. Selenium-supplemented foals are known to grow better than Se-deficient foals, possible because a Se-dependent enzyme is needed to activate thyroid hormone.

In addition, both males and females require selenium for reproductive function.

Exercise increases oxidative metabolism markedly, which results in mobilization of tissue selenium to meet increased antioxidant demand. This explains why performances horses and human athletes have greater selenium needs than non-athletes.

Is Organic Selenium more or less toxic than inorganic selenium?

Although more digestible than inorganic selenium, organic selenium is actually much safer to both horses and humans. The organic selenium compounds that plants and yeast produce are nature’s way of providing a potentially toxic element in a safe form. Selenoamino acids are absorbed from the gut via amino acid pathways, which necessarily limits excessive uptake.

In contrast, inorganic selenium (selenite) is passively absorbed, which allows rapid and unregulated uptake of toxic levels of selenium. Organic Selenium is also much safer to handle by those mixing feeds. Sodium selenite is extremely toxic because it is absorbed through the skin. In contrast, the compounds of organic selenium are not absorbed on contact, which increases safety against the most common selenium toxicity problem: exposure to human skin.

Selenium decreases immunity and only organic selenium allows for proper muscle recovery from exercise.

For a long time we have believed that selenium deficiency decreases disease resistance. Selenium is as critical to horse health as any vaccination that you could give. Here is the story:

At the University of Kentucky they fed horses a selenium deficient diet and naturally they became selenium deficient. They also monitored GPx status, an enzyme that relieves oxidative stress in muscle tissue after exercise. They found:

“Immune function assessment of the horses indicated that low selenium status was detrimental to the immune system.”

“Also, following exercise the horses of low Se status experienced a decrease in GPx activity which did not recover within 24 hours. This occurred even though the exercise was mild with the recreational riding horse in mind. GPx activity increased post-exercise in horses supplemented with Se-yeast (organic) but decreased in the inorganic Se group (Sodium Selenate)”

This further validates the importance of supplementing organic selenium when horses are fed a selenium deficient diet.

This information is taken from the Equine Disease Quarterly Newsletter, October 2013. It is produced by the Gluck Equine Research Center at the University of Kentucky.