The locoweed is a herb which gets its name from the Spanish word for 'crazy' because horses, cattle and sheep behave strangely after eating it.
They either run wildly, bumping into objects that come in their way, or become dull, drag their feet, eat infrequently, lose muscle control, become thin and finally die.
Scientists believe that the locoweed absorbs poisonous elements from the soil. The effect it has on animals depends upon the soil in which it grows. It is a perennial plant that grows in western North America. There are a few varieties of locoweeds that have no effect on animals.