Common Name
Paintbrush, Indian Paintbrush
Botanic Name
Castilleja species
Plant Family
Mountains and plains.
Animals Affected
Horses, cattle
Toxic Principle
The plant is a secondary selenium accumulator if growing in high selenium soils. Selenium exerts its toxicity by replacing sulfur in proteins. In the keratin molecule of the hooves and hair this weakens the structure resulting in the characteristic breakage of long hairs in the main and tail of horses. Affected keratin tends to be abnormal in formation and is weakened at the site selenium is incorporated into its molecular structure.
Annual or perennial plants which are herbaceous but many are woody at the base only. The leaves are alternate and sessile. The zygomorphic flowers are arranged in terminal, bracted spikes. The bracts are usually petaloid ranging from scarlet to yellow in color. The calyx is tubular and four-lobed, more deeply cleft above and below than on the sides. The corolla is long and narrow, strongly two-lipped, the upper, called a galea, is elongated and the lower lip is very short and three-toothed. The stamens are four, in pairs, and are enclosed by the galea. Paintbrush attach to the roots of surrounding plants (sage species) in a symbiotic relationship.
Successful treatment of selenium poisoning is dependent on early recognition of signs and the removal of livestock from the source of the excess selenium. Feeding a high protein diet with adequate copper levels may help counteract the effect of selenium on sulfur containing amino acids. Recovery from chronic selenium poisoning will occur in time if the animal is fed a diet low in selenium and high in sulfur containing amino acids.
Integumentary System
The long hairs, especially those of the mane and tail tend to break off at the same point giving the animal a "bob" tail and "roached" mane appearance.
A diagnosis of selenium 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.
Special Notes
Paintbrush is rarely if ever a problem to livestock.