Australian stringhalt

Veterinary advice should be sought before applying any treatment or vaccine.

Australian Stringhalt

Pasture-associated Stringhalt

Australian stringhalt, also known as pasture-associated stringhalt, is a debilitating neurological condition of horses characterized by an abnormal gait and involuntary extreme hyper (over) flexion of the hindlimbs when attempting to walk. Australian Stringhalt can occur in individual horses sporadically or in outbreaks involving multiple horses turned out together in the same pasture.
Australian Stringhalt occurs in horses worldwide. Outbreaks of AS have been well documented in horses in the United States, United Kingdom, New Zealand, Australia, France, Chile, and Japan. Onset is often seasonal, with more cases diagnosed during dry conditions in late summer or fall. It was first reported over 120 years ago in horses in south-eastern Australia.

Australian Stringhalt is one of three different forms of stringhalt that have been documented in horses. It is caused by grazing in pastures containing certain plants that are considered toxic to horses. The most common being catsear (Hypochaeris radicata), also known as flatweed. In one study, it was reported that 65 out of 66 paddocks with horses that developed AS, contained catsear.

The specific toxin in the plant, known to cause stringhalt has not yet been identified. It is thought to be related to a possible fungal contamination, related to mycotoxins similar to that seen in horses with ryegrass staggers.

Horses with Australian Stringhalt have such an extreme hindlimb hyperflexion such that the hindlimb may make contact under the belly when they try to take a step forward. The abnormal gait is caused by involuntary control of the hindlimbs. Recovery can take anywhere from a few days to 18 months. The average recovery period is 6-12 months.

There may also be a relationship between Australian stringhalt and Recurrent Laryngeal neuropathy (RLN) in horses.


Abnormal gait
Hind limb hyperflexion
Muscle atrophy
Aggressive behavior


  • History
  • Clinical signs
  • Physical exam
  • Confirmation of plant in pasture



Removal from sourceRemove flatweeds from horse pastures and/or relocate horses to different pastures that do not contain flatweeds and have quality grass coverage.
Dilantin® (phenytoin)An anticonvulsant drug which helps ease the signs of the disease and help hasten recovery. Typical dosage is 15 mg/kg administered orally as a paste or mixed within feed, q12 hrs for 2 weeksHuntington et al., 1991
SurgeryInvolves removing the lateral digital extensor tendon in the hind leg


  • Make yourself aware of the weeds and plant species that can be invasive in pastures and/or poisonous to horses.
  • Take periodic walks around pastures to check for the presence of potentially poisonous plants
  • Check that hay does not contain dried up poisonous plants
  • If you borrow or hire farm machinery ensure it is clean prior to arriving on your property, the same goes for lending of your own equipment.
  • Quarantine new animals in a separate paddock the first 10 days to 2 weeks after arrival. Weed seeds can be passed through an animal's digestive tract.


50% of horses usually recover within 8 months.

Scientific Research

General Overviews

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Risk Factors

  • Older horses
  • Tall horses (over 17 hands)
  • Draft horse breeds
  • History of grazing on pastures containing flatweed.
  • Prolonged dry summers
  • Horses on poorly maintained pastures.

Horse Case Stories