The Effects of Excess Selenium in Horses

Horses nutritional needs vary depending on the type of activity they do, their age and whether they are gestating or nursing their young. Small amounts of minerals are critical to the health of horses, as they are in humans, but an excess of some minerals can have serious effects. Selenium is necessary to the horse̵7;s diet, but it can cause severe health deterioration when ingested in large amounts.

  1. About Selenium

    • Selenium is an essential trace mineral found in plant foods. It combines with proteins to make seleno-proteins which are antioxidant enzymes. Antioxidants protect the horse̵7;s body from free radicals, which are by-products of normal oxygen metabolism. Selenium deficiency can cause muscle disease, difficulty in suckling and swallowing, impaired heart function and respiratory distress in horses. Selenium is only required in small amounts to be effective, however. The Federal Drug Administration has set a recommended amount of selenium for horses at 3 milligrams per day, according to the American Association of Equine Practitioners website. In some areas of the country, forage resources may be so high in selenium it can cause toxicity. Blood testing is the only way to determine the level of selenium in your horse̵7;s body.

    Mane and Tail Deterioration

    • One of the signs of excess selenium ingestion is breakage of the horse's hair in the mane and tail. The breakage can give the tail a bobbed appearance and the mane a roached, or shaved, look. If you see unexplained changes in your horse̵7;s mane and tail hair, consult with your veterinarian about testing to determine if excess selenium is the problem.

    Hoof Changes

    • Excessive amounts of selenium can also cause hoof problems in horses. Rings, cracks and ridges develop that cause a poor appearance and pain. The hooves can become so deteriorated that lameness develops. The hooves can even be lost by the severe deformities caused by excess selenium.

    Excessive Salivation

    • Too much selenium in the horse̵7;s forage can also produce excessive salivation. This effect may be accompanied by other signs of digestive upset such as upset stomach and diarrhea. Investigate the horse̵7;s forage areas to determine if plants contain an excessive amount of selenium that may cause these effects.

    Respiratory Problems

    • Excessive selenium can also cause respiratory effects, such as labored breathing, difficulty in swallowing and ultimately, respiratory failure. The excess amount of selenium can cause weakness in the muscles of the heart and respiratory system that progressively worsen and can lead to death.