Locoweed Poisoning in Horses

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

What is Locoweed Poisoning?

Locoweed is a name that encompasses a large number of different plants, a portion of which are poisonous. All of the varieties look similar to one another and unless a person is very knowledgeable about plants they will likely not be able to tell each one apart from another. This being the case, it is important to treat all varieties as if they are poisonous. The majority of the species are either herbs without stems or with small stems. The plants have flowers that are different colors along with pods of a variety of sizes and shapes. 

Found mainly in the western United States, these plants do well in dry soil and an environment that is semi-arid. Horses will typically avoid locoweed, unless they are lacking in food to eat.

Covering a large number of types of plants, only a portion of which are poisonous, locoweed is mainly found in the western United States and can lead to a variety of symptoms in your horse.

Symptoms of Locoweed Poisoning in Horses

Should your horse experience locoweed poisoning, you may notice the following symptoms:

  • Salivating excessively
  • Wandering around aimlessly
  • Seeming uncoordinated 
  • Ongoing weight loss (uninterested in eating and drinking)
  • Problems with vision
  • Appearing lethargic, then showing excessive outbursts to minor stimuli
  • Infertility in stallions

Your horse may appear to “go crazy” or “loco”.


The plant may be toxic as a result of alkaloids or because it is a selenium accumulator. In the cases of toxicity due to alkaloids, the toxicity will lessen upon the drying of the plant over time. If the toxicity is because of being a selenium accumulator, the toxicity will remain after the plant has dried. This is because drying has no impact on selenium accumulation.



Causes of Locoweed Poisoning in Horses

The plant contains a toxic compound called swainsonine, an alkaloid that causes parts of the nervous system to swell after it has had a long period of time to accumulate in the body of your horse. This alkaloid would have to be ingested for at least fourteen days before it would lead to a reaction in your horse. 

The other reason the plant can be poisonous is that some species are selenium accumulators, and horses can only handle a small amount of selenium over the recommended intake amounts. In many cases, selenium accumulator plants have significantly higher levels than those considered to be safe.



Diagnosis of Locoweed Poisoning in Horses

Your veterinarian will conduct a full physical examination of your horse and ask you questions about what symptoms you have noticed, when you first noticed them and what changes have occurred. Your horse may undergo testing to determine the levels of swainsonine in his blood and tissues. His urine may also be tested to see if the concentration of mannose-containing oligosaccharides is high.



Treatment of Locoweed Poisoning in Horses

Should your horse experience locoweed poisoning, you will want to keep him away from the source of the toxin. If it is not possible to remove the plant from where he grazes, you will have to keep him away from the area. It is important to do this right away or the poisoning will continue. Even after trying it once or twice, a horse can become addicted to locoweed. Once he is no longer ingesting the locoweed, some of his symptoms may diminish, though in many cases behavioral changes in your horse will be permanent.

In addition to keeping your horse from the plant, your veterinarian will consider administering sedatives and laxatives in an effort to rid your horse of this poison. Mood elevators may also be used (for example tranylcypromine, protriptyline and reserpine).

Should your horse no longer have access to locoweed prior to showing advanced symptoms, he will be able to recover, though recovery will be slow.



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Recovery of Locoweed Poisoning in Horses

Should your horse be recovering from locoweed poisoning, it is likely that follow up appointments with your veterinarian will be necessary. This will give your veterinarian the opportunity to examine your horse, see how the treatment is going, and make any changes as appropriate.  It will be important to follow the recommendations of your veterinarian to ensure the best outcome for your horse.

To avoid your horse experiencing locoweed poisoning, it is a good idea to become aware of the weeds and plant species that can be invasive in pastures as well as poisonous to horses. You can walk around your pastures on occasion to make sure that potentially poisonous plants are not present. Remember that dried up plants may also be an issue.



Locoweed Poisoning Questions and Advice from Veterinary Professionals

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