Poisoning is common in sheep, but occurs occasionally in cattle.
The plant is poisonous to livestock throughout the growing season. Losses are heaviest when hungry animals are trailed through Colorado rubberweed or are placed on overgrazed ranges with heavy infestations of Colorado rubberweed. All aboveground parts of the plant contain a poisonous sesquiterpene lactone. Animals grazing the plant may have a gradual buildup of the toxin to the level that it is harmful or lethal, or they may eat large amounts of Colorado rubberweed and be poisoned immediately. Colorado rubberweed is a small, bushy plant about 0.5 meter high that grows on dry areas of the West.