Dry plains and foothills, usually on alkaline soils.
Horses, cattle, sheep.
Saltbush will accumulate high levels of selenium when growing in selenium-rich soils. Animals that eat it and other forages in the area have the potential of developing chronic selenium poisoning. Excess selenium in the diet causes abnormal hair and hoof formations as a result of selenium replacing sulfur in keratin, the primary protein in hair and hoof.
A perennial shrub that is woody throughout, loosely branched, the bark gray, scaly and scurfy. The leaves are mostly alternate, often covered by a white powdery substance. The plants are dioecious with staminate flowers in terminal panicles without bracts. They have a three to five-parted perianth and 3-5 stamens. The pistillate flowers, produced in leaf axils, are subtended by 2 bracts, but are without a perianth. The fruits have 4 conspicuous wings.
Lameness due to hoof wall deformity and horizontal cracks in the hoof walls. All feet are usually affected.
Affected animals should be removed from any food or water source containing more than 5 ppm. Diets containing adequate amounts of sulfur and copper have a protective effect against chronic selenium poisoning. Alfalfa has sulfur-containing amino acids and is a useful food source in areas where forages are high in selenium.
Animals with chronic selenium poisoning have defective keratin formed in their hair and hooves with the result that the hair breaks off at the point where selenium is incorporated in the hair. The hoof walls have horizontal ridges form where selenium is incorprated in the keratin. These ridges form cracks in time that can cause severe lameness.
A diagnosis of selenium chronic poisoning is best confirmed by submitting samples of hay or forages for analysis. Selenium levels greater than 5 ppm should be considered potentially toxic. Blood levels of 1-4 ppm are typical of chronic selenium poisoning, whereas serum levels up to 25 ppm have been reported in acute poisoning. Liver and kidney levels greater than 4 ppm are indicative of selenium toxicosis. Hoof wall containing 8-20 ppm is indicative of chronic selenosis. Hair samples containing in excess of 10 ppm selenium indicate excessive selenium intake capable of causing toxicity.