Locoweed

(Astragalus and Oxytropis species)

Locoweed is poisonous to horses.



Plant Description

The name locoweed covers approximately 200 varieties of plants, but very few (approximately 20) of these plants are actually poisonous. However, they all look very similar, and in some cases it is impossible for anyone except a very experienced botanist to tell them apart. Therefore it is prudent to treat all species as if they are poisonous.

Most of the species are small stemmed or stemless herbs. They have flowers of varying colors as well as small pods that vary in size and shape. Their seeds are the shape of a kidney bean.

Geographic Locations

These plants are found primarily in the western United States, ranging from the Great Plains to the Rocky Mountains. They prefer dry soil and a semi-arid environment.

Toxic Plant Components

All fresh plants are toxic. If the plant is toxic because of alkaloids, the toxicity will gradually reduce as the plant dries over time.

However, if it is toxic due to being a selenium accumulator, then the plant will remain toxic after being dried, as selenium accumulation is not affected by drying.

Toxicity Cause and Symptoms

Locoweed is toxic for two reasons. The first is that it has a toxic compound, swainsonine, that is an alkaloid. This alkaloid causes swelling of components of the nervous system after it accumulates in the body for a time. It must be consumed for a period of at least two weeks before it causes a reaction.

The second reason they can be poisonous is because some species are selenium accumulators. Horses can tolerate very little selenium above the recommended intakes, and accumulator plants often have levels drastically beyond the safe level.

Symptoms of poisoning include:

  • Excessive salivation
  • Aimless wandering
  • Uncoordination and altered gaits
  • Chronic weight loss
  • Vision Problems
  • Lethargy followed by extreme outbursts in response to mild stimuli
  • Stallion infertility
  • Mid- to late-term abortions in mares

In general, it appears that the horse has gone crazy, or "loco", thus the name of the plant.

Cure and Treatment

The cure for locoweed poisoning involves administering sedatives and laxatives while keeping the horse as quiet as possible. The earlier the horse is removed from the source of toxicity, the better.

Horses can become addicted to locoweed after tasting it a few times, so it must be completely removed from their access to prevent continual poisoning.

The earlier in the disease that the horse is removed, the better his prognosis will be. If access to the plant is removed before he starts showing advanced symptoms, he will usually have a slow but successful recovery from the toxicity.


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