Hoof Nutrition Intelligence is a twice-a-month web segment that is designed to add to the education of footcare professionals when it comes to effectively feeding the hoof. The goal of this web-exclusive feature is to zero in on specific areas of hoof nutrition and avoid broad-based articles that simply look at the overall equine feeding situation.
Below you will find Part 2 of the latest question and answer installment that you can share with your footcare clients.
Q: What is the role of selenium with both hoof quality and overall horse health?
By Mieke Holder
Named after the Greek word for moon, selene, selenium (Se) is a unique trace mineral that has held scientists’ fascination for decades.
One of the first discoveries made about selenium was its ability to prevent necrotic liver disease in rats. Years later, researchers found selenium is an essential component of the antioxidant enzyme glutathione peroxidase. They determined that selenium is specifically incorporated into proteins to form selenoproteins.
This knowledge led to the discovery of at least 25 different selenoproteins in the body. More than half are believed to play a role in the antioxidant mechanism. Because of this antioxidant mechanism role, researchers believe selenium affects some body systems such as the immune system and immune responses.
However, not all selenoproteins involved in the antioxidant mechanism play roles in other systems. Regardless of the number of functions that selenium fulfills, only small amounts are required in the equine die. It also has a relatively narrow safety margin.
The selenium content of forages and grains commonly fed to horses depends on a soil’s selenium content and soil pH. Therefore, it varies geographically. As an example, central Kentucky pastures, and hay grown locally, tend to be low to marginal in selenium content.
Selenium can be supplemented in an inorganic (such as sodium selenite) or organic (such as selenium yeast) form. Commercial horse feeds are typically formulated using either one of these sources of selenium, which is usually indicated on the feed label. Since a portion of the needed selenium will be contributed from the forage in the horse’s diet, it is important to follow the manufacturer’s recommended feeding rates.
The current dietary selenium recommendation (in the National Research Council's Nutrient Requirements of Horses, 2007) is a total of 1 milligram (mg) per day for a mature 1,100-pound horse, even those doing light exercise.
Recommendations increase to 1.25 mg per day for lactating broodmares or heavily exercising 1,100-pound horses. A maximum tolerable limit of 2 mg of selenium per kilogram of dry matter has been set to account for the narrow safety margin.
U.S. Food and Drug Administration guidelines state that 3 mg per day is a safe daily limit for livestock species. Commercial feeds formulated for higher-level competition horses often provide a total dietary selenium intake closer to 3 mg per day to maximize the potential antioxidant benefit that selenium can provide to these athletes. Research is ongoing in determining the exact nature of these benefits.
If you’re considering adding additional mineral supplements to your horse’s diet, always work with a nutritionist or veterinarian. Considering the total dietary mineral content diet is especially important for a mineral like selenium, which can have potentially lethal consequences if oversupplied.
Mieke Holder is a researcher in the department of animal and food sciences at the University of Kentucky.
Hoof Nutrition Intelligence is brought to you by W.F. Young Co. (Absorbine). 
Like many significant achievements, Absorbine® grew out of humble beginnings—and through the tenacity of someone willing to question the status quo. In this case, it was a young woman in late 19th-century Massachusetts: Mary Ida Young. Her husband, Wilbur Fenelon Young, was an enterprising piano deliveryman who relied on the couple’s team of horses to make deliveries throughout the Northeast. Inspired by Mary Ida and Wilbur’s vision, Absorbine® has continued to add innovative products throughout the years — products used every day by horse owners around the world. Which is why, since 1892, we’ve been The Horse World’s Most Trusted Name®.
Click here to read Part 1 of the January 15, 2018 installment: How do I know if the improvement in my horse's hooves is due to supplements or a change in temperature?
Click here to read more installments of Hoof Nutrition Intelligence.