Purple Locoweed Poisoning in Horses

PurpleLocoweed Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
PurpleLocoweed Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Purple Locoweed Poisoning ?

The toxin swainsonine works on cellular enzymes, causing a build-up of sugars within the lysosomes which digest intracellular waste. This build up causes the formation of fluid filled cavities within the cell which changes the regular performance of the body functions. Swainsonine is water soluble and rapidly absorbed by the body. Your horse may recover physically once removed from the affected pasture, but the effects on the brain remain permanent and there is no proven effective treatment for this condition, with locoed horses having a poor prognosis in regards to recovery.

Locoweed has over 200 species of these plants, with swainsonine, an indolizidine alkaloid toxin, causing pathological changes to body tissues in your horse causing locoism.

Symptoms of Purple Locoweed Poisoning in Horses

Your horse may start exhibiting strange behavior such as over reacting when touched, or violent movement causing falls or dangerous behavior 

  • Early warning signs includes acute depression and lack of energy, your horse may act sleepy or may not move very much at all 
  • Once the toxin affects the neurological performance your horse may lose control of its movement 
  • After a large amount of the toxin has been ingested, you may notice sudden weight loss 
  • Incoordination, head hanging or nodding, or even an exaggerated high stepping pace
  • Your horse may frighten easily, reacting violently and unexpectedly


  • Purple (and white) locoweed has over 200 or so species of these pretty but poisonous plants 
  • The characteristic purple (or white) flowers and swollen pods, and green leaves signify its presence
  • It is by far the more widespread dangerous plant in the Western United States 
  • All parts of the plant are toxic, including foliage, seeds, flowers and pollen
  • The rainy seasons trigger the growth of the locoweed seeds in the ground
  • It grows prolifically in dry sandy soils


Causes of Purple Locoweed Poisoning in Horses

  • This poisonous plant seems to affect horses more than cattle, with elevated levels of the toxin remaining higher throughout the grazing season in horses
  • Horses seem attracted to eating the plants green foliage during periods of drought or lack of good feed
  • It causes partially metabolised sugars to build up in the brain affecting cellular function 
  • The longer your horse eats this toxic plant, the symptoms and effects will worsen 
  • Once the toxin has damaged vital brain cells, the process is irreversible 


Diagnosis of Purple Locoweed Poisoning in Horses

Because of the close bond between yourself and your horse, if he has been eating locoweed there is a real threat of danger to you from the unexpected behaviour of your horse.  The possibility of severe injury is high if your horse has been affected. Sudden movements from such a powerful animal pose a substantial risk to humans. Prevention is by far the best course of action, as there is no known or proven cure for your horse once he has eaten a toxic dose. Even removing him from the affected pasture will not help if the toxin has attacked the brain cells. Once the toxin starts affecting the brain cells, the damage done cannot be reversed. Your horse will remain nervous and will not return to his former personality. 

The fact that locoweed is a hardy plant and produces attractive green foliage when other feed has turned brown make it enticing and lethal for grazing animals. Monitoring your pasture and keeping your horse away from it while you work to eradicate the pest is essential. Locoweed thrives in dry sandy soil, and heavy rains can promote its growth.  Providing alternative feed for your horse while your pastures undergo cleansing is the only course of action available. 

The veterinarian will note the clinical signs present in your horse such as sleepiness and lack of coordination. He may also do blood tests to look for markers indicative of purple locoweed (oligosaccharides and swainsonine).



Treatment of Purple Locoweed Poisoning in Horses

While removing your horse from the pasture is vital, the real test for recovery is how long has your horse been eating the locoweed. If you have only just noticed this weed and acted quickly, getting your horse out of the field before he gets a taste, he will have a good chance of recovery. But sadly, there is no remedy for your horse if he has had exposure to this plant, and once the toxin has made its way into the brain the damage has been done. With a case of severe toxicity, even the best of care for over a year will not cure your horse of the effects.

The uncertainty of the behavior means being cautious in regards to safety. This is paramount as your horse may be easily frightened and react as if to spook, so that must be kept in mind especially if you have young family members. Loud noises and unexpected handling can cause the most violent reaction. Even if your horse seems recovered, riding a loco horse remains a risky procedure. The other thing to consider is that horses once affected seem to be addicted to the plant and if it is growing in the pasture, they will be drawn to eat it. So vigilance is always the key. Your veterinarian may prescribe medication to calm your horse, but at this stage there no treatment to reverse the damage caused by this pretty but lethal plant.



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Recovery of Purple Locoweed Poisoning in Horses

In areas where this plant is well known, people are always alert to the tell-tale signs of this plant creeping into pasturelands. An effective management plan is essential to ensure your horse will lead a healthy life. The cost of treating the pasture with herbicides and planning the treatment cycle of various paddocks as far as rotation and alternative feed for stock must be considered. But keep in mind that there is no cure for purple locoweed, it is devastating to your horse, and if you are in a farming situation it can cause damage to cattle stock. As well as the effects on the animal consuming the plant, it can also affect the unborn or the newborn as it is passed onto the young though the parent. The loss of both your horse and the new foal is a real threat which makes prevention the only real option.



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