Veterinary advice should be sought before applying any treatment or vaccine.


Locoweed Poisoning, Swainsonine Toxicity

Locoism, also known as locoweed poisoning, is a neurological condition in horses caused by chronic consumption of locoweed plants. Locoweeds are perennial flowering plants that are considered to be one of the more serious poisonous weeds to livestock. There are 44 different types of locoweeds, many of which are most commonly found in grasslands and rangeland areas. There have been numerous cases of locoism in horses, sheep, and cattle throughout the World. Different types of locoweeds grow in different regions throughout the world.

Types of Locoweeds
Plant GenusFound
Astragalus and OxytropisWestern United States and China
Swainsona Australia
Ipomoea carneaMozambique
Sida carpinifolia and TurbinaBrazil

Toxic component
Locoweeds contain swainsonine, a type of indolizidine alkaloid that is toxic to horses and other animals if ingested over a long period of time. The chemical has a significant inhibitory effect on alpha-mannosidase in lysosomal and inhibits glycoprotein synthesis, resulting in lysosomal storage disease in affected horses.
Horses with locoism develop neurological and behavioral disorders, as well as gait abnormalities causing abnormal posture, symmetrical ataxia, posterior limb peresis, emaciation, and difficulty standing. Clinical signs of locoism are observed after a few weeks to months of consuming locoweeds in contaminated pastures.


Altered, often aggressive behavior
Refusal to eat or drink
Gait abnormalities
Difficulty standing and walking
Visual impairment
Abnormal posture
Symmetrical ataxia
Staggered gait
Dull appearance


  • History
  • Clinical signs
  • Histopathologic lesions
  • Blood and tissue levels of swainsonine
  • High urine content of mannose-containing oligosaccharides



Remove horses from the locoweed sourceThis may alleviate some of the associated clinical signs, however in most cases the behavioral changes are usually permanent.
Mood elevatorsCombinations of mood elevating medications such as tranylcypromine, protriptyline and reserpine might be beneficial.


  • Attention should be placed on avoiding over grazing. Horses generally will not eat locoweed as part of their diet unless other forage isn't available.
  • Make yourself aware of the weeds and plant species that can be invasive in pastures and/or poisonous to horses.
  • Take periodic walks around pastures to check for the presence of potentially poisonous plants
  • Check that hay does not contain dried up poisonous plants
  • If you borrow or hire farm machinery ensure it is clean prior to arriving on your property, the same goes for lending of your own equipment.
  • Quarantine new animals in a separate paddock the first 10 days to 2 weeks after arrival. Weed seeds can be passed through an animal's digestive tract.


Removal from exposure to the plants can result in some alleviation of signs, however behavioural changes may be permanent.

Scientific Research

General Overviews

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Risk Factors

  • Letting horses graze in pastures containing locoweed plants
  • Not knowing what plants are growing in horse pastures

Also Consider