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What is False Dandelion Poisoning?

False dandelion is also called flatweed and catsear.  The botanic name for false weed is hypochaeris radicata.  False dandelion is similar in appearance to the common dandelion but the flowers are larger.  False dandelion is palatable to horses, so if it is growing in the pasture your horse will gladly ingest it.  If your horse is showing symptoms of false dandelion poisoning it is important to immediately remove him from the pasture he has been foraging on.  He needs to be seen by an equine veterinarian as soon as possible.

False dandelion poisoning in horses occurs when a horse grazes on the plant for an extended period of time.  False dandelion poisoning affects the horse’s peripheral nervous system, which causes lameness and a sudden hyperflexion of the gambrel joint of one or both hind legs. The sudden hyperflexion of the gambrel joint is referred to as stringhalt gait.

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Symptoms of False Dandelion Poisoning in Horses

Symptoms may include:

  • Lameness
  • Hyperflexion of the gambrel joint, also called hock joint
  • Dragging hind legs
  • Muscle atrophy
  • Roaring sounds (false dandelion poisoning can affect the larynx or voice box)

Causes of False Dandelion Poisoning in Horses

False dandelion poisoning in horses is caused by the extended ingestion of the plant, affecting the peripheral nervous system. The actual toxin in the plant has not been identified. The plant is palatable to the horse; therefore he will continue to forage on it. It is important to maintain the pasture your horse grazes on.  This includes regularly checking and removing trees, plants and weeds that may be toxic to your horse.

Diagnosis of False Dandelion Poisoning in Horses

The veterinarian may want to go over the medical history of the horse and ask to see deworming and immunization records.  He will want to know what symptoms you have noticed and the evolution of them.  The veterinarian may want to see your horse walk on a lead so that he may see his gait.  If a poisonous plant is suspected, he may want to see where the horse forages. The large, bright yellow flowers of the false dandelion plant are easily found.

During the physical examination the veterinarian may take the patient’s pulse, blood pressure and weight.  He may want to listen to the sounds of your horse’s gastrointestinal tract and his lungs.  The patient’s pupils and the inside of the mouth may be checked. The veterinarian may palpate your horse’s limbs and evaluate the muscle tone. The veterinarian may want to run a few diagnostic tests.  Additionally, he may recommend x-rays and an ultrasound to rule-out any physical injuries to the horse.

Treatment of False Dandelion Poisoning in Horses

Your horse must not be allowed on the pasture until the false dandelion is removed.  The more false dandelion the horse ingests, the more damage to the nerves will result.  The patient may be started on fluids via an intravenous to keep him hydrated and to help administer medications.  Thiamine may be recommended; the supplement is known to have a calming effect in horses. The horse may be prescribed phenytoin orally. Phenytoin is an anticonvulsant drug. The veterinarian may also suggest physical therapy to help your horse rebuild muscle tone.  Therapy for false dandelion poisoning may involve months and even years.  

There are recent studies that show that treating false dandelion poisoning with botulinum (Botox) can help reduce the clinical signs. The treatment plan is under investigation.

Recovery of False Dandelion Poisoning in Horses

Horses experiencing less severe symptoms of false dandelion poisoning have a better prognosis to make a full recovery. Your horse will need follow up visits to monitor his progress.  The veterinarian will want to see how the horse is responding to the medications and physical therapy.  

It is imperative that the false dandelion plants are removed from the pasture.  The plant may be manually removed or the use of an herbicide may be helpful.  Proper pasture management is important for the health of your horse as many toxic plants and weeds can be fatal if ingested. The pasture must be regularly checked for toxic weeds. Beneficial plants and grasses should be available for the horse to forage on.  If you are not certain what plants may be poisonous to your horse and other animals (livestock, dogs, or cats for example), contact your local agricultural agent.  He can help you identify what plants are toxic and what plants you should have growing on your property for your horse to enjoy.