angle-left Toxic Horse Plants: Locoweed

Toxic Horse Plants: Locoweed

Locoweed is one of the most common poisonous plant for horses in the West, and its effects are staggering.

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By Sara Gugelmeyer for Ranch Horse Journal

Locoweed is a widespread poisonous plant problem in the Western United States, according to New Mexico State University Extension Range Specialist Emeritus Chris Allison, Ph.D. Locoweed is a broad term used for nearly 400 species of toxic horse plants, Astragalus and Oxytropis, found throughout the West. 

All parts of the locoweed plant is toxic to horses and contain swainsonine, an alkaloid that causes: 

  • pathological changes in body tissues 
  • disrupted cellular function and wreaks havoc on whatever consumes it

If grass is green, horses will typically avoid locoweed. However, if consumed, within 48 hours:

  • Permanent damage is done to the horse’s brain and nervous system causing abnormal behavior, or “locoism.”
  • The horse will always seek it out once it consumes it. 
  • Other animals will model that behavior and eat the loco as well. 

Locoweed is aptly named. It literally makes animals that eat it crazy or “locoed.” And because of the devastation it can cause to ranchers’ horses and cattle, it even makes those who deal with it crazy.