First Walk is on Us!

✓ GPS tracked walks
✓ Activity reports
✓ On-demand walkers
Book FREE Walk

Jump to Section

What is Toxic Equine Parkinsonism?

Toxic equine Parkinsonism in horses is also referred to as chewing disease and equine nigropallidal encephalomalacia.  Russian knapweed and yellow star thistle are most common to the Northwest and California.  The continual foraging of these toxic plants causes brain lesions, which leads to muscle paralysis. The muscle paralysis renders the horse unable to swallow food or water.  In desperation, some horses submerge their heads in the water troughs in the attempts to drink water. 

In most cases, the neurological damage is irreversible.  There are experimental and natural treatments that may provide some relief to the symptoms of toxic equine Parkinsonism. If your horse is showing signs of equine Parkinsonism he must be immediately removed from the pasture he has been foraging on.  He must be seen by an equine veterinarian as soon as possible.

The continuous ingestion of yellow star thistle (centaurea solstitialis) and/or Russian knapweed (centaurea repens) causes neurological damage that impairs the horse’s ability to swallow and causes hypertonic (fixed facial expression) facial muscles. These clinical signs of toxic equine Parkinsonism are similar to Parkinson’s disease symptoms in people.

Book First Walk Free!

Symptoms of Toxic Equine Parkinsonism in Horses

Symptoms may include:

  • Paralysis of the lips and tongue
  • Reduction of jaw tone
  • Mouth open with tongue hanging out
  • Weakness
  • Depression
  • Drowsiness
  • Standing in unusual positions
  • Incoordination
  • Difficulty breathing
  • Muscle tremors
  • Anxious and confused behavior
  • Hypertonicity of the muzzle and facial muscles
  • Head hanging low
  • Excessive yawning
  • Constant chewing 
  • Violent head tossing
  • Weight loss
  • Dehydration
  • Malnutrition 
  • Mouth abrasions and ulcers
  • Inability to swallow 
  • Inhalation pneumonia may develop

Causes of Toxic Equine Parkinsonism in Horses

Toxic equine Parkinsonism in horses is caused by the continual foraging of large amounts of Russian knapweed and/or yellow star thistle. The reasons the horse will continue to eat these toxic plants:

  • The horse will ingest the plants if there are no other plants to forage on
  • Russian knapweed or yellow star thistles have overtaken the pasture
  • Horse acquires a taste for the plant

Diagnosis of Toxic Equine Parkinsonism in Horses

The veterinarian may want to go over the horse’s medical history.  If your horse has been seen by another veterinarian, it is recommended that you bring the medical records.

The veterinarian will want to know what symptoms you have observed and when did they start.  He may want to take a walk on the pasture the horse forages on.  The veterinarian may be able to visually identify the toxic plants.

The doctor will perform a physical and neurological exam on the patient. The horse’s weight, pulse and blood pressure may be taken.  The veterinarian may palpate the horse’s abdominal area and muscle tone.  He may check the mobility of the patient’s neck. The horse may have his reflexes tested. The veterinarian may want to listen to the horse’s lungs with a stethoscope.

The doctor will be able to diagnose toxic equine Parkinsonism from the clinical signs.  The veterinarian may suggest a magnetic resonance imaging (MRI) scan, which can determine the extent of neurological damage. If inhalation pneumonia is suspected, chest x-rays may be recommended.

Treatment of Toxic Equine Parkinsonism in Horses

In most cases the neurological damage caused by toxic equine Parkinsonism is irreversible.  If the horse is dehydrated, the veterinarian will administer fluids via intravenous. The use of glutamine synthetase plus bovine brain gangliosides extract has been reported to be beneficial in some horses.   Cerebral vasodilators and high doses of thiamine and vitamin E may also help alleviate the symptoms of toxic equine Parkinsonism in horses. Cerebral vasodilators improve the blood flow to the brain. Tube feeding will need to be done while the horse is being treated. Patients with inhalation pneumonia may be prescribed antibiotics and nebulizer treatment.

Recovery of Toxic Equine Parkinsonism in Horses

Toxic equine Parkinsonism in horses has a grave prognosis.  Follow-up visits will be necessary to monitor how the horse is responding to the treatment plan. Most horses do not improve, even with a treatment plan. The horse’s quality of life must be considered, the veterinarian may recommend euthanasia.    

In most cases, toxic equine Parkinsonism in horses is considered a disease of neglect. The early detection and removal of these toxic plants can help prevent the poisoning. Toxic plants may be removed manually or the use of herbicides may be necessary. Responsible horse owners regularly monitor their pastures. Additionally, the horse must be provided good plants to forage on such as tall grass, forbs, and legumes.