Common Name
Woody Aster
Botanic Name
Xylorrhiza glabriuscula
Plant Family
Prefers the dry alkaline soils at altitudes from 4000-6000 feet. Selenium is esstenial for growth, making woody aster an indicator plant for selenium-rich soils.
Animals Affected
Horses and cattle
Toxic Principle
Woody aster will accumulate high levels of selenium. It is consequently seldom eaten by livestock. As an obligate selenium accumulator, its presence in the area is indicative of selenium-rich soils, and other plants in these soils will also contain selenium. 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.
Erect perennials up to 2 feet in height, arising from a woody base and tough tap root. Leaves are hairy, linear-oblanceolate and tipped with a callus point. The ray flowers are white.
Horses, in particular, may become severely lame. Initially circular ridges forms in all feet. As the hoof wall grows out, the ridges may crack and lames can be severe due to lamimitis and even sloughing of the hoof.
Affected animals should be removed from food or water sources 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.
Integumentary System
Chronic selenium poisoning causes loss of the long hairs of the mane and tail.
Samples of hay or forages containing 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.
Hoofwall cracks - chronic selenium poisoning