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 1 of the latest question and answer installment that you can share with your footcare clients.
Q: Is there a concern when it comes to hoof quality from feeding excess amounts of selenium?
By Karen Briggs
A: While selenium is actually a trace or micromineral rather than being categorized as a macromineral, it has a huge influence on hoof health. Even though it’s needed only in very small amounts, it has received a great deal of press in recent years.
Function:Selenium works in partnership with vitamin E as an important antioxidant and both work best when present in the correct amounts. In addition, selenium also plays a role in the control of thyroid hormone metabolism.
Signs Of Toxicity:Unlike most minerals which have a broad safety range, selenium has a very low threshold of toxicity for horses — only a few parts per million (ppm) beyond the recommended levels. Thus the assumption that “if some is good, more is better” is particularly dangerous and the effects of selenium toxicity can be worse than the effects of a deficiency.
Deficiency symptoms include patchy sweating, blind staggers, colic, diarrhea and increased heart and respiration rates if acute (as for example, when a horse is given selenium injections). In chronic cases, a selenium deficiency can lead to a loss of hair, especially in the mane and tail, the cracking of hooves around the coronary band and hooves that occasionally slough off completely.
The selenium content of feeds varies depending on where the plants were grown, as the soil content of selenium fluctuates significantly across North America. Some areas are so selenium-deficient that crops grown there are considered to contain no selenium at all, necessitating supplementation. A few crops have toxic concentrations of selenium, making any supplementation positively reckless.
Due to extreme variations from region to region, regulations exist in Canada and in most of the United States that require feed companies to print a warning to consumers whenever selenium is added to a feed.
Because the toxicity threshold of selenium is so low (between 2 and 5 ppm), your footcare clients should be aware of the selenium content of local soils (and thus pasture and your hay) before choosing a vitamin E and selenium supplement, or a selenium-added feed. Some trace-mineral salt blocks contain added selenium, so the label should be checked before placing a salt block in a pasture.
The level of selenium currently recommended for horses is between 0.1 ppm and 0.3 ppm (dry matter).
Karen Briggs is an equine nutritionist in Everett, Ontario, is a riding instructor and has managed farms and riding schools in her career.
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 2 of the September 15, 2015 installment: How can an owner tell if the poor quality of a horse’s hooves is due to a lack of proper nutrients?
Click here to read more installments of Hoof Nutrition Intelligence.