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What is Crofton Weed Poisoning?

Crofton weed can be an erect, perennial plant or a small, soft-stemmed shrub. There are several woody stems that are covered in sticky hairs when the plant is young. These hairs can be reddish, green or purplish in color. When the plant matures, the stems become woody and turn brown or a brownish-green. The roots are yellow in color and give off a carrot-like smell when they are broken or damaged. The crofton weed will have dense clusters of white flowers in the spring and summer.

Most horses will prefer to graze on crofton weed because of the carrot-like smell produced from the roots and the slightly sweet taste of the young stems. Continued access to crofton weed will cause your horse to become ill in as little as eight weeks. The first symptom of crofton weed poisoning will be a persistent cough that is made worse by exercise. Lung and heart damage can occur if your horse is allowed to continue eating crofton weed. Death will occur from respiratory failure if left untreated.

Crofton weed has several names including catweed, sticky eupatorium, Mexican devil, sticky snakeroot and maui pamakani. Scientifically, it is known as Ageratina adenophora. The crofton weed is native to Mexico, but has been transplanted across the United States and Canada as an ornamental bush.

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Symptoms of Crofton Weed Poisoning in Horses

If you notice any of these symptoms, contact your veterinarian immediately for an emergency call. Remove your horse from their pasture and put them into their stall with plenty of fresh, clean bedding. Do not give them any food, including hay, until your veterinarian directs you to do so.

  • Coughing that is worse when they exercise
  • Exercise intolerance
  • Shortness of breath
  • Depression
  • Loss of conditioning
  • Respiratory distress 
  • Collapse
  • Heart failure
  • Death

Causes of Crofton Weed Poisoning in Horses

All parts of the crofton weed are extremely toxic to horses when ingested. The toxic compound is A. adenophora. Crofton weeds are very palatable to horses and they will many times prefer to graze on the weed rather than other forage in their pasture. The toxin builds within your horse’s system and symptoms of crofton weed poisoning will begin to present in as little as eight weeks with continual grazing on crofton weed. If your horse continues to eat crofton weed after the first symptoms appear, death may occur quickly as the respiratory system and cardiovascular system are affected by A. adenophora.

Crofton weed is the most toxic soon after it flowers in the spring. There is new research that suggests the pollen from the flowers on the crofton weed will also cause poisoning since the pollen also contains the A. adenophora toxin.

Diagnosis of Crofton Weed Poisoning in Horses

There are no known diagnostic tests available to conclusively identify crofton weed poisoning in horses. Since it can take anywhere from eight weeks to several years for the toxins to fully affect your horse, pinpointing the source can be difficult.

Your veterinarian will begin by doing a physical examination of your horse. This will include a complete blood count, urinalysis, and fecal examination. These tests will help your veterinarian determine what the illness is not and be able to narrow their search.

An ultrasound of your horse’s lungs and heart will also be done. Your veterinarian will be searching for any damage that might have already occurred due to the toxins building up in your horse’s body. The presence of damage to the lungs and/or heart will allow your veterinarian to diagnose the illness as crofton weed poisoning.

Treatment of Crofton Weed Poisoning in Horses

Any treatments given by your veterinarian will most likely not reverse any damage already done to your horse’s heart and lungs. Therefore, early detection is essential in keeping your horse from suffering long-term effects from the toxins.

Your veterinarian will provide supportive care for your horse including intravenous fluids and proper nutritional support. Medications may be given to treat the symptoms as they present. Stall rest may be recommended while your horse is being assessed and new symptoms are appearing.

Some veterinarians may try antibiotics or corticosteroids to treat crofton weed poisoning in horses. These treatments have not been documented well enough to know if they are an effective method of treatment. If the damage is too severe to your horse’s lungs or heart, euthanasia is recommended.

Recovery of Crofton Weed Poisoning in Horses

Any damage that is done to your horse’s respiratory and cardiovascular systems will be irreversible. Most horses that have been diagnosed with crofton weed poisoning will not be able to perform work any longer. Exercise should be kept to a minimum and. They should be able to recover enough to become a pasture horse.

Practice good pasture management and remove any crofton weeds found in or near your pasture. Since these plants are so palatable to your horse, you need to be aware of their presence and eradicate them as soon as possible.