Cocklebur (Xanthium strumarium) is an annual plant that grows in lakebeds, river bottoms, and in disturbed and flooded areas of fields, pastures, and roadways. Poisoning occurs primarily in cattle, sheep, horses, and swine when the plant is eaten in the cotyledon stage (seedling). Signs of poisoning include rapid, weak pulse, labored breathing, nausea, vomiting, and spasmodic contractions of the legs and neck muscles.
Desert baileya (Baileya multiradiata) is a small annual that grows in the dry, sandy and gravelly areas from Texas to southern California. Sheep are sometimes poisoned on this plant. Signs of poisoning include depression, anorexia, and slobbering of a green material from the mouth.
Drymary or inkweed (Drymaria pachyphylla) is a short-lived annual that grows close to the ground on alkaline clay soil in western Texas, southern New Mexico, and Arizona. Poisoning occurs primarily in cattle. Signs of poisoning include loss of appetite, diarrhea, restlessness, arched back, depression, coma, and death. Drymary is exceedingly distasteful to livestock.
Horsetail (Equisetum spp.) is a herbaceous perennial. It is rushlike in appearance with hollow, jointed stems. This group of plants is common throughout the United States. It is toxic primarily to horses and cattle.
Jimsonweed or thornapple (Datura spp.) is a large annual herb with worldwide distribution. It is toxic to all classes of livestock. Signs of poisoning include subnormal temperature, restlessness, muscular twitching, incoordination, paralysis, and respiratory paralysis. Poisoning in humans is not uncommon.
Tansy mustard (Descurainia pinnata) is an annual weed that grows on dry, sandy soils in arid areas. Intoxication occurs primarily in cattle only after large amounts of this plant have been eaten over extended periods of time. Signs of poisoning include partial or complete blindness, inability to use the tongue, and aimless wandering.
Yellow star thistle (Centaurea solstitialis) is an annual weed growing throughout much of the Eastern, Southern, and Western United States. It is toxic primarily to horses. Signs of poisoning include twitching of lips, tongue flicking, involuntary chewing movements, and drowsiness. Animals have difficulty eating and drinking but can swallow. Russian knapweed and other species of the knapweed may also be toxic.
Hundreds of plants are poisonous to livestock. Many are toxic at all times, whereas many others are toxic only under certain conditions. Livestock producers are urged to become acquainted with the plants on their ranges and pastures that are potentially dangerous to their livestock. Help in identifying these plants can usually be obtained from the local county agricultural agent. Help with poisonous plant problems can also be obtained from local veterinarians.