Lambert Crazyweed, Loco

Oxytropis lambertii

Fabaceae (Legume family)


Lambert crazyweed is a perennial legume that often forms colonies by short rhizomes, with larger plants forming mounds. Moisture and temperature greatly influence the abundance of vegetative growth, and the plants sometimes die completely back to thick root crowns. Leaves arise directly from the root crown and are up to 8 inches long, with nine to 19 leaflets. The leaflets are hairy, and each silky hair is attached at its center with both ends free. Pink-purple to almost white flowers are displayed in terminal spikes on leafless stalks. The pods are sessile, oblong, beaked, silky and curved backward or inward.


The plant grows primarily on well-drained sandy or gravelly soils and often on rocky knolls in north central Texas, in the Panhandle and on the High Plains. It extends into similar regions of New Mexico, Oklahoma, Colorado and Kansas.

Toxic Agent

The toxic agent is the alkaloid swainsonine, which causes an enzyme dysfunction resulting in damage to the brain, liver, digestive organs, placenta, ovaries and testes. Cell damage is reversible except in the brain.

The plant is toxic to cattle, sheep, goats and particularly horses. Horses may display signs after consuming 30 percent of their body weight of the plant, and the lethal dose is around 75 percent of their body weight.

Cattle and sheep display signs of locoism after eating about 90 percent of their body weight over a 2-month period, and lethal doses in ruminants are usually around 200 to 350 percent of their body weight over several months.

Signs of Livestock Ingestion

Signs result from the involvement of sensory and motor functions. In cattle, general signs include: Carrying the head a little lower than normal; Vacant stare; Trembling of the head; Difficulty or inability to eat and drink; Infertility or subfertility in males and females; Abortion, or deformed or weak offspring.

Swainsonine is passed into the milk, leading to the unthriftiness of some suckling calves. Poisoned horses are listless, but become excessively excited to the point of stumbling when stimulated suddenly. Horses with chronic locoism rarely recover and are permanently dangerous to ride.

Management Strategies

Livestock imported from areas where loco does not grow are the most susceptible to poisoning. Native animals generally avoid locoweed when good quality forage is available. Maintaining good range condition and a sound supplemental protein and mineral feeding program is the best prevention against locoism. Individuals observed eating loco should be removed to a locoweed- free pasture. Grazon P+D® can be applied to individual plants or broadcast to control plants dominating a particular area. Treated plants become much more toxic and palatable until they are completely dry.