Article: Simplifying Selenium Supplementation.

Publication: Island Horse Magazine

Author: Alexa Linton, Equine Sport Therapist, Kinesiologist

Date: June 18/2006

In the confusing world of equine nutrition, supplementation of the trace mineral selenium is definitely one of the more unnerving subjects. It is not only toxic or possibly deadly in high amounts, but a deficiency can be equally detrimental. Venturing into the topic as a horse owner and an equine therapist, I happened upon several very interesting facts about selenium supplementation, which seem especially pertinent considering our geographical situation on Vancouver Island .

Selenium is a trace mineral or micro-mineral, an essential nutrient performing key metabolic functions in your horse's body. Besides selenium, other essential trace minerals include copper, zinc, iodine, manganese, iron, cobalt, and fluorine. These minerals are “required”, albeit in small amounts, and are often a forgotten part of a diet program, as many owners assume adequate amounts will be consumed as a part of our horse's natural forage, grains, and feeds. In fact, trace minerals can often make the difference between a horse that is very healthy and happy and one that is most definitely not.

More and more on Vancouver Island , we run into the phrase “selenium deficiency.” Unfortunately for our horses, the forage they receive is very low in the trace mineral selenium, which in small amounts is a powerful anti-oxidant and detoxifier for the body systems. Not long ago, the discovery of selenium in glutathione peroxidase, an incredibly important enzyme, helped to clarify the essential role of selenium in the protection of cellular membranes against toxins and free radicals. Anti-oxidants such as selenium and vitamin E are our first line of defense against cellular damage by free radicals, and are essential for the proper functioning of the immune and muscular systems. Symptoms of deficiency can include muscular atrophy, lameness, sweating, and overall muscle pain. This deficiency can make many activities, including riding and even grooming uncomfortable for your horse.

In many parts of the world, the soil contains adequate amounts of selenium, and supplementation is not necessary. Unfortunately, certain regions of the world have very high levels of selenium in the soil, causing plants growing in the area to have similarly high levels. There are certain plants which tend to accumulate toxic levels of selenium, namely the astragalus genus. Consumption of forage containing high levels of selenium can cause toxicity, also called “alkali disease” in horses in a short time, resulting in loss of hair from manes, breath that smells of “garlic”, lameness, infections within the hoof, neurological malfunction, respiratory distress and occasionally death. Reports have also been made of cases of toxicity resulting from excessive use of supplements, environmental contamination and selenium in water. In fact, due to its dangerous properties, the FDA continues to monitor its inclusion in animal feeds. Hence, the understandable tendency to be cautious about supplementing this particular trace mineral.

So, here on Vancouver Island we are given the daunting task of walking the fine line between too much and not enough. In fact, it is very possible your horse may have a selenium deficiency that you have not noticed or identified. Blood tests performed by your local veterinarian, designed to measure the levels of minerals in the body, can help ease your mind and get your trace mineral supplementation back on track by providing a solid baseline.

With trace minerals, the typical measurement is parts per million (ppm) or as milligrams per kilogram (mg/kg) of dry matter (DM) feed. Although the figure seems to change slightly, the most consistent figure for a minimum requirement of selenium for a horse per day is 0.1 ppm, although a level of 0.1 – 0.3 ppm is generally recommended. This would translate to 1 to 3 mg of selenium per day. Selenium supplements come in many forms, including a vitamin and mineral supplement such as Dr. Reeds, a pelleted feed with added selenium, a trace mineral lick, or a separate selenium supplement (usually combined with vitamin E). These supplements tend to contain fairly low levels of selenium, so that it is difficult for an owner to mistakenly overfeed. As feed companies tend to strictly obey the safety regulations for trace minerals, an owner can stay safely away from toxicity by following the feeding directions for their chosen selenium supplement.

But don't go rushing out for a selenium supplement yet. It is also important to understand the different types of selenium available for your horse's consumption. As with humans, some forms are more easily absorbable and utilized by the body. There are two categories we need to remember, inorganic and organic. Essentially, organic selenium is attached or associated with a compound that contains carbon, the most common example being selenium-enriched yeast. The inorganic form contains no carbon and is often chemically formulated, with the most common form being sodium selenite. It has been proven in research that not only is a higher percentage of the organic form of selenium (selenium-enriched yeast) absorbed than the inorganic form, sodium selenite, but selenium-enriched yeast seems to be more effectively stored and utilized within the selenium-dependant processes in the body. There is also evidence that the organic form tends to be safer than the inorganic forms, albeit more expensive and difficult to find.

Although my hope was to “simplify” selenium, it is possible that you are more confused than when you begun. In this case, take the opportunity to do your own research on the supplementation of selenium and the other trace minerals for your horse. Also, don't hesitate to ask the advice of a professional, as they can often help you to prevent discomfort due to trace mineral deficiency or toxicity in your horse before it begins. And as always, happy horsing around!

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