Locoweed is the name of a large group of poisonous herbs that grow in western North America. Locoweeds have harmful effects when they are eaten by horses, cattle, or sheep. The name locoweed comes from the Spanish word for crazy, because of the strange actions of animals poisoned by the plants.
There are about a hundred kinds of locoweeds. Two of the more common kinds are the Lambert crazyweed and the woolly loco. Locoweeds have erect or spreading stems with many leaflets on each stem.
The effect of locoweeds on animals depends on the soil in which the plants grow. Scientists believe that the plants’ poisonous effects result from their ability to absorb large amounts of the element selenium from the soil.
The symptoms of poisoning vary somewhat in horses, cattle, and sheep. Horses become dull, drag their legs, eat infrequently, and lose muscle control. Soon they become thin and die. Cattle react in much the same way. But sometimes they run wildly about, bumping into objects in their path. Sheep react more mildly to the poison.
Animals that are raised on a range usually do not eat locoweeds when other food is available. Ranchers destroy locoweeds by cutting the roots about 2 inches (5 centimeters) below the surface of the soil, or by spraying the plants with a herbicide.
