Australian Stringhalt

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

Australian Stringhalt

Pasture-associated Stringhalt

Australian Stringhalt Overview


Australian Stringhalt (AS), 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. AS can occur in individual horses sporadically or in outbreaks involving multiple horses turned out together in the same pasture.
Image of prolonged hyperflexion of limb in a horse with Australian Stringhalt
AS occurs in horses worldwide. It was first reported over 120 years ago in horses in south-eastern Australia. The condition is one of three different forms of stringhalt that have been documented in horses; however the pasture-based or outbreak form of stringhalt is generally referred to as Australian stringhalt. 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. There has been a great deal of evidence from various research studies that associate the presence of a certain plant, commonly referred to as catsear (Hypochaeris radicata), in pastures with horses that develop AS. In one study, it was reported that 65 out of 66 paddocks with horses that developed AS, contained catsear. However the particular toxin contained in the plant that causes AS has yet to be confirmed. It is suspected that it is associated with possible fungal contamination, related to mycotoxins similar to that seen in horses with ryegrass staggers.

Catsear
Also known as flatweed, Hypochaeris radicata is a common, yellow-flowered perennial herb that is found worldwide in horse pastures. It looks very similar to, and is closely related to dandelions (Taraxacum genus); they are both part of the Asteraceae plant family. It has a large, often branched tap root which allows it to be a very drought-tolerant plant, enabling it to survive during periods of long dry summers.

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

Symptoms

Abnormal gait
Hind limb hyperflexion
Muscle atrophy
Depression
Aggressive behavior

Diagnosis

  • History
  • Clinical signs
  • Physical exam
  • Laboratory tests

Treatment

TherapiesDetails
Removal from sourceRemove flatweeds from horse pastures and/or relocate horses to different pastures that do not contain flatweeds and have quality grass coverage.
Phenytoin15 mg/kg administered orally as a paste or mixed within feed, q12 hrs for 2 weeks to help improve clinical signsHuntington et al., 1991
Acupuncture
Mephensein
Baclofen
Surgery

Prognosis

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.

Seasonality

WinterSpringSummerAutumn