by J.G. Davis, T.J. Steffens, T.E. Engle, K.L. Mallow, S.E. Cotton 

Introduction
Selenium (Se) is an essential nutrient for the health of humans and animals.  New claims that Se may reduce liver disease and prevent or even cure cancer have encouraged some people to look to Se to cure their ailments. However, excess Se can be toxic to both humans and animals.  Selenium from the soil is absorbed by plants, and when livestock eat those plants, Se toxicity may develop.  Selenium toxicity was first reported in farm animals in China in the 13th century, but the first documented report in the United States occurred during the 1850s in South Dakota.

Se toxicity in livestock can occasionally be acute (one-time consumption of toxic Se levels) or more commonly chronic (consumption of lower, but elevated, Se levels over a long period).  Acute selenium toxicity is often called “blind staggers,” although the affected livestock are not always blind nor staggering. Recent research has shown that blind staggers is sometimes associated with high sulfur intake and is not always due to Se toxicity.  Typical symptoms of blind staggers include head pressing, perspiration, blindness, abdominal pain, colic, diarrhea,increased heart and respiration rates, and lethargy.  Death can occur quickly.

Chronic Se toxicity is called “alkali disease” and is characterized by dullness and lack of vitality; roughness of coat; loss of hair (especially around the mane and tail of horses and the tail switch in cattle); hoof soreness, overgrown or deformed hooves, horizontal ridging, cracking and even sloughing of hooves or complete loss of the hoof wall; and stiffness and lameness.

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