It’s never bad to be aware of things that may be toxic to your horse, but precautions can be carried too far if you don’t know the details. Yes, selenium is a potentially toxic mineral (they all are) but deficiency is much more common.
An owner contacted me because she had a hay selenium assay done which showed she was feeding about 3 mg per day from the hay, but she was horrified to realize the horse had been receiving another 2 mg per day on top of that. The bare minimum requirement for an average size horse is 1 to 2 mg/day.
However, bare minimum requirements are a long way away from toxic and even the 5 mg/day is considerably below any intake that would be dangerous. It is estimated an average size horse would need to take in at least 20 mg/day to be at risk for chronic toxicity – i.e. toxicity that takes weeks to months to show up. Acute toxicity takes over 1500 mg/day.
Naturally occurring chronic toxicity can occur with hays having over 5 ppm selenium ( = 50 mg in 22 lbs of hay) but this is rare. Natural toxicity is more likely in animals grazing on very high selenium soils where wild selenium accumulator plants, which contain several hundred ppm selenium, are growing. The highest selenium soils in the USA occur in pockets of Wyoming and South Dakota. These soils are high saline shales with an alkaline pH.
Acute toxicity causes a neurological derangement called “blind staggers” and is fatal. Chronic toxicity, “alkali disease”, causes loss of mane and tail hair plus disrupted hoof growth resulting in separation of the hoof capsule at the coronary band. Another symptom of selenium toxicity is a DMSO or garlic-like odor on the breath. Recovery from chronic toxicosis takes up to 10 months if the hooves slough off. Again, both of these are rare.
Severe selenium deficiency causes white muscle disease, with degeneration of skeletal and heart muscle. This is usually seen in foals but can also affect adults. Adult deficiency has also been linked to atrophy of the cheek muscles and swallowing difficulty. A link to tying-up has not been confirmed but wild animals with deficiency develop extensive muscle breakdown when they are chased in attempts to capture them. Many studies have shown how selenium protects the muscles, lungs and red blood cells from damage caused by free radical generation during exercise. Selenium also plays critical roles in the normal functioning of the immune system and is needed for generation of the active form of thyroid hormone, T3.
It’s important to realize that the selenium dose in supplemented grains or vitamin/mineral supplements, which is regulated by law, is not going to cause toxicity even if intake from hay is already adequate. There is a lot more to worry about from deficiency than toxicity. If you have any concerns regarding whether your horse’s selenium intake could be toxic, consult your veterinarian. Selenium status is easily checked with a blood test.
Uckele Health & Nutrition, maker of CocoSoya, features supplements that provide balanced Selenium support.
Selenium Yeast Blend is an organic chelated Selenium Yeast Blend in a palatable Brewer’s Yeast base. Perfect for feeding Selenium without adding Vitamin E. Commonly deficient in horses, Selenium yeast for horses supports muscle tissue, the heart, and the nervous system. It also promotes a healthy immune system by neutralizing the damaging effects of excessive oxidative stress and free radicals.
Selenium-E Gel is an organic chelated Selenium yeast blend for heart and skeletal muscle support. Convenient, high-potency gel also supports healthy muscle and immune function.
E+ SE Pellet or Powder. Commonly deficient in horses, concentrated levels of important antioxidants E and Selenium work together to support a healthy immune system, support the cells and tissues of the body, and neutralize the damaging effects of excessive oxidative stress and free radicals. Available in a palatable powder or a pellet.
E+SE 10X provides concentrated natural Vitamin E and organic Selenium Yeast that work together to support healthy immune, cardiovascular, and immune function. Low levels of Selenium in the soil is common in many regions, and Vitamin E levels drop drastically when the grass is cut for hay.
About Dr. Kellon
Dr. Eleanor Kellon, staff veterinary specialist for Uckele Health & Nutrition, is an established authority in the field of equine nutrition for over 30 years, and a founding member and leader of the Equine Cushings and Insulin Resistance (ECIR) group, whose mission is to improve the welfare of horses with metabolic disorders via integration of research and real-life clinical experience. Prevention of laminitis is the ultimate goal. www.ecirhorse.org
Uckele Health & Nutrition, maker of CocoSoya, is an innovation-driven health company committed to making people and their animals healthier. On the leading edge of nutritional science and technology for over 50 years, Uckele formulates and manufactures a full spectrum of quality nutritional supplements incorporating the latest nutritional advances. www.uckele.com.
Contact: Susan Libby, email@example.com