b'NUTRITIONSelenium BalanceMieke Holder, MS, PhD, assistant professor of nutrition and environmental impact in the University of Kentuckys Depart-ment of Animal and Food Sciences, in Lexington, knows selenium. She dedicated her doctoral research to better understanding how a horses selenium balance affects his antioxidant status and immune function.Antioxidants in the body help protect cells from damage by molecules known as free radicals. Selenium is a vital part of an antioxidant known as glutathione peroxidase. What sets selenium apart from other trace minerals is how it is incorporated into the functional parts of various proteins, she says. Through these selenoproteins, the bodys selenium concen-tration affects the antioxidant system, immune function, andRegional distribution of forages and grains in North America containing low, other physiological pathways. Selenium is toxic at relatively lowvariable, or adequate selenium levelslevels, and a horse only requires about 1 milligram of selenium per day (for a 1,100-pound idle horse; NRC, 2007). However, Low: Approximately 80% of all forages and grain contain <0.10 parts per million soil selenium concentrations and, therefore, plant selenium(ppm) seleniumcontent, vary across the United States (see map). For example, Variable: Approximately 50% contain >0.10 ppm selenium (includes Alaska)about 80% of forages and grains produced in areas up and Adequate: 80% of all forages and grain contain >0.10 ppm selenium (includes down the East Coast contain less than 0.1 parts per million ofHawaii)selenium. Researchers have found that blood selenium levels de-crease below adequate levels in unsupplemented idle horses grazing pastures with marginal selenium. However, due to a high toxicity risk, supplementation of selenium in addition to that provided by your horses forage, commercial feed, or balancer pellet should only be done in consultation with a nutritionist, says Holder.Kristen Janicki, MSFat-soluble vitamins, including vita- in the liver and adipose (fat) tissue forto consume or synthesize these continu-mins A, D, E, and K, cannot be absorbedlater use.ously for use because they are not stored by the small intestine and transportedWater-soluble vitamins, includingin the body.into the bloodstream without the pres- vitamin C and the B-complex vitamins,Fresh forages provide most of the vi-ence of fat. The body can also store themdissolve readily in water. The horse needstamins horses need, and grazing pasture covers the daily vitamin requirements for most classes of horses. But once cut and conserved, forages experience vitamin losses, so horses not on pasture might need extra vitamin support. Fortunately, horses can make or store most of the nec-essary vitamins themselves and, even in times of dietary deficiency, can synthesize or mobilize enough to meet their needs. Most commercially produced concen-trates include at least some fat-soluble vitamins in their formulations. For the diet do-it-yourselfer, the ever-growing pool of vitamin supplements offers indi-vidualized options, as well. As with other nutrients, vitamin requirements vary depending on the horses life stage, with broodmares and their fetuses needing the most throughout gestation and for milk production. Aged, diseased, or perfor-mance horses might need supplemental vitamins to provide additional immune support. 26September 2019The Horse | TheHorse.com'