Australian Stringhalt
By Nicole Salo

  Australian stringhalt (ASH) is an exaggerated hyper flexion of the hock. Australian stringhalt causes the horse to walk with an exaggerated forward and upward motion of one or both back legs. In mild cases, the horse may only be noted to having an odd gait while backing up, turning or during cold weather. This is not the case with severe Australian stringhalt, the affected horse will move in an exaggerated motion as if the horse’s leg were glued to its belly.

  Australian stringhalt was first reported in Australia in the mid-1800s, it has also been seen in New Zealand and the United States. Although Australian stringhalt is idiopathic, it is thought to be induced by toxic plants or fungi and possibly deficiencies in nutrients. Flatweed (Hypochaeris radicata) or “cat’s ear” is thought to be the leading contributor to Australian stringhalt. Flatweed is often mistaken for dandelion (Taraxacum officinale) as their flowers and leaves look similar. Flatweed grows fruitfully all through Australia and has been noted in Canada and in both the eastern and western United States.

  Australian stringhalt is mainly a seasonal disorder seen in herds grazing weedy pastures during late summer and autumn. It often affects more than one member of the herd, but it is unknown why it does not affect the whole herd (possibly all the horses are not grazing the same area/have immunity), affecting 10-15% of the herd. Many cases of Australian stringhalt show dramatic muscle deterioration of the digital extensor group (gaskin.) Only a few horses have been seen to have muscular damage of the forelimb, this was seen mainly in draft horses. Australian stringhalt may also lead to some degree to left recurrent laryngeal neuropathy (laryngeal paralysis, roaring) which is almost always a problem seen in athletic horses with Australian stringhalt.

  Thoroughbreds are most commonly affected with Australian stringhalt, accounting for 48% of the documented cases. Australian stringhalt also tends to affect horses that are taller than 15 hands high (accounting for 84% of the cases documented.) It seems to target mature horses more often than younger ones, and it shows more severe signs in horses that are normally nervous or apprehensive.

  Diagnosis of Australian stringhalt is rather easy in a sense. It can not be detected by radiographs or through blood tests, but rather by watching the horse’s way of going. It may be hard to determine mild cases of Australian stringhalt by the untrained eye; severe cases will not be mistaken though. If it is suspected that a horse has Australian stringhalt, the horse’s handler can do a simple task of asking the horse to back up which may confirm the condition through the horse’s exaggerated gait. At which time, a veterinarian should be called to rule out other disorders such as upward fixation of the patella, joint or feet problems which can be confused with mild Australian stringhalt. Treatment is determined by the severity of the condition.

  Australian stringhalt generally is the worst during the first month after the disease is found. It usually resolves on it’s own with regaining of lost muscle and the gait returning to normal. Given enough time, Australian stringhalt will normally resolve itself. Horses can recover in as little as two weeks. While it can take up to several years to resolve, it is most common for the disease to dissipate within six to nine months time.  Most horses can be used fully a couple months before they have completely recovered from Australian stringhalt, as they begin to show only minimal alterations to their gait. Horses that develop left recurrent laryngeal neuropathy as a side effect to Australian stringhalt may need surgery to repair the laryngeal function before they can be worked again.

  Although horses eventually recover without any treatment, some treatments may be tried. The best treatment is to remove the horse from the pasture where the signs were first noted. The horse can be safely returned to the pasture after the autumn break when the weeds that may be causing the disease have died off. Surgical removal of a part of the extensor tendon running over the hock is often over looked with Australian stringhalt unless it is necessary to improve the quality of life for the horse.

  There are products being tried that may be used as medical therapies in the near future to treat Australian stringhalt. One of the drugs being tested at the University of Melbourne in Victoria, Australia, is called Dilantin (extended phenytoin sodium), which is used to treat epilepsy in humans and other animals. It has been tried with successful results in reducing the severity of the exaggerated gait in Australian stringhalt. Vitamin E may be used as an antioxidant treatment for nerves; as well magnesium and vitamin B1 may be added to the therapy. Most treatments are unrewarding as it is unsure exactly what causes Australian stringhalt. Horses generally cope well with Australian stringhalt; it is the most nerve-wracking for the owner of the horse.

  The best preventative measure is to graze horses on relatively weed-free pastures and paddocks. Avoid over grazing your fields so that they do not become over run with weeds and little grass encouraging the horse to graze on toxic weeds like Flatweed that could cause Australian stringhalt. If Flatweed is noted to be growing in a pasture, eradicate the weed before allowing horses to graze the pasture. The best measure to avoiding Australian stringhalt is a preventative one.

About Nicole
Nicole Salo is an equine entrepreneur and founder of The Morning Feed with experience in various parts of the industry, including: training, breeding, management, horse racing and equestrian social media with a background in off the track Thoroughbreds and American Quarter Horses. Nicole has studied Equine Science, Equine Studies and Equine Business Management.

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Comment by Geoffrey Pannell on April 19, 2011 at 6:10pm

I think your'e right!! They have to eat an awful lot to kill them though. It does give them the squirts. Not seen too much of the other one, Flat weed , about.

Cheers geoffrey

Comment by Nicole Salo on April 19, 2011 at 9:23am
Hi Geoffrey, I think you may be confusing the two plants, although one may cause stringhalt, the other is a known cause. Capeweed (Arctotheca calendula) may cause stringhalt in horses, and yes it is an immigrating species from South Africa. I believe that horses and livestock can die from over eating Capeweed due to nitrate poisoning, and much less worse is horses (and donkeys) are prone to skin reactions when encountering the plant. Flatweed - more commonly known as Cat's ear in Australian (Hypocherus radicata) is a known trigger point for stringhalt in horses, although why is still unknown. Below are some photos, the daisy looking low to the ground weed is Capeweed (first photo), the much taller weed with dandelion looking flowers is Flatweed/Cat's ear (second photo).

Comment by Geoffrey Pannell on April 18, 2011 at 7:45pm
we call it Capeweed here Nicole, I've not heard it called Flatweed. It is easy to control with a broadleave herbicide. Iv'e just finished spraying it here , It's quite hard to eradicate because it gets into inaccsesable places but easy to manage if you spray at the right time. Only had three or four horses with it over the years. I always thought it came over from South Afrika, hence the name Capeweed. If left unchecked it will take over a pasture in double quick time.
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