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Pasture-Associated Stringhalt in HorsesBy Kentucky Equine Research Staff · May 2, 2017

Pasture-associated stringhalt (PSH) is much like traditional stringhalt, in that it is characterized by exaggerated, spasmodic flexion of the hindlimbs. In contrast to stringhalt, PSH also features peripheral neuropathy*. Turning and backing seems to exacerbate excessive flexing of the limbs, and an unusual hopping gait sometimes accompanies the disease.

PSH is sometimes referred to as Australian stringhalt. Though the condition was initially identified in Australia and New Zealand, cases have cropped up in Asia, Europe, North America, and South America.

The plant most commonly linked to PSH is Hypochoeris radicata, also known as false dandelion, flatweed, or cat’s ear, though poor-quality, drought-scarred pasture is thought also to be implicated. Other plants have been associated with stringhalt or stringhalt-like gait abnormalities: Lathyrus species (sweet peas), Taraxacum officiale (dandelion), and Malva parviflora (marshmallow). A neurotoxin or neurotoxins within these plants is believed to cause stringhalt and PSH, though no specific neurotoxin has been identified yet.

False dandelion is considered an invasive weed, and because of its long taproot, it can resist drought or difficult growing conditions more readily than other pasture plants. This resiliency means that false dandelion is often the last vegetation to die off in a drought-affected pasture.  

Treatment of horses affected by pasture-associated stringhalt is not straightforward. The obvious first step is to eliminate exposure to false dandelion. Management strategies include surgery (myotenectomy of the lateral digital extensor), botulinum toxin infiltration, and muscle relaxants. From a nutrition perspective, several supplements have been tried: thiamine, taurine, and antioxidants (vitamins E and C), for example. The effectiveness of these nutritional supplements in ameliorating signs of PSH has not been measured.

Many horses recover from toxicity, but it is usually a protracted convalescence, possibly lasting 6-18 months, though mild cases may recover more quickly. Severe cases, on the other hand, might take as long as two years for full recovery to occur, and a few horses never recover completely.

Avoiding PSH might be as simple as implementing a key management changes.

  • Most cases of PSH are diagnosed when horses have access to unimproved pastures, often in times of drought. Make the most of pastures with routine fertilizing, reseeding, and weed control measures. Consult with a pasture specialist to make the pasture as nutritionally rewarding as possible. Renovating pasture can be costly, but the reward in good-quality forage is worth the expense.
  • When drought or other conditions affect pasture quality, provide horses with alternative forage sources, such as free-choice hay. Researchers have noted that horses will consume false dandelion even when other pasture plants are available. It is, therefore, imperative that you provide horses with something more palatable than weeds.

*El-Hage, C.M. P.J. Huntington, I.G. Mayhew, R.F. Slocombe, and B.S. Tennent-Brown. 2017. Pasture-associated stringhalt: Contemporary appraisal of an enigmatic syndrome. Equine Veterinary Education. In press.