Common Name
Penstemon, beard tongue
Botanic Name
Penstemon species
Plant Family
Widespread in well drained soils of the mountains ans plains.
Animals Affected
Horses and ruminants
Toxic Principle
May accumulate selenium if growing in selenium-rich soils.
Usually erect herbaceous perennials, but many species are low and creeping. The leaves are opposite, simple and without stalks (sessile). The flowers are showy, tubular with the upper lip 2 lobed, and the lower 3 lobed. Flower color varies from blue to red to white. There are 4 fertile stamens and a fifth conspicous sterile (staminode) is hairy at the apex, giving the plant its name beard tongue.
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 wall.
Affected animals should be removed from any food or water source containing more than 5 ppm of selenium. 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.
Special Notes
Penstemons are rarely a problem to livestock themselves, but as facultative selenium accumulators, serve to indicate the potential for other forages high in selenium.
Penstemon spp.
Circular hoofwall crack of chronic selenium poison