Selenium

What it does

Selenium works with vitamin E to prevent nutritional muscular dystrophy, equine degenerative myeloencephalopathy and equine motor neuron disease ^[1].

Deficiency

Deficiency lowers serum selenium and raises AST, and causes white muscle disease and perhaps tying-up (rhabdomyolysis) in working horses ^[1]. Acidic soils in some regions are deficient, and horses there may need supplementation ^[1].

Toxicity

Selenium has a very narrow range of safety ^[1]. Forage grown on alkaline soils in some regions can contain enough selenium to be toxic ^[1].

Signs of acute toxicity include apparent blindness, head pressing, sweating, faster heart and breathing rates, and lethargy. Chronic toxicity causes loss of mane and tail hair and cracking of the hoof at the coronary band ^[1].

Idle mature horses gain no advantage from extra selenium above their requirement ^[1].

Interactions

Excess copper may reduce selenium absorption ^[1].

See also vitamin e, copper.