Stringhalt in Horses: Causes and How To Treat
What Is Stringhalt?
Stringhalt is described as a non-painful neuropathic condition of horses that is characterised by an abnormal hindlimb gait. It is easily recognisable because the horse will tend to lift and maintain the hindlimb in excessive flexion and kind of ‘jump forward’ and slam it down. We can see this when the horse is walking forwards and backwards.
The following video displays the typical appearance of stringhalt.
Often these horses are more severely affected at the walk, and as the gait increases in speed, the clinical signs disappear. This is why you might notice some interesting gaits of racehorses when they are walking around the birdcage, yet they can gallop perfectly.
Some horses are affected in both hind legs, while others may only be affected in one hind limb.
Scientist and veterinarian researchers still are unable to tell us exactly what stringhalt in horses is caused by, however, it does appear to be two types of stringhalt in horses:
- True (idiopathic) stringhalt and
- Sporadic, or pasture-associated stringhalt
True stringhalt is one of those conditions that have us all scratching our heads. It often occurs in older animals, and frequently only one hindlimb is affected. There doesn’t appear to be any breed or activity links or a relationship to nutrition or environment.
The only hint of a cause for True Stringhalt is there may be evidence of an injury to the lateral digital extensor tendon or dorsum of the metatarsus (front of the cannon).
In contrast, sporadic or pasture-associated stringhalt appears to be associated with consumption of False Dandelion (Flat Weed, Cats Ear). We often see this type of stringhalt in an outbreak usually associated with a distinct seasonal pattern.
The most common times we see this in Australia and NZ is at the end of summer when there have been drought conditions and paddocks are bare. A little rain can see a flush of growth from these weeds and of course, horses will eat the plant quickly!
False Dandelion or Flat Weed Toxicity in Horses
While the common dandelion (Taraxacum officinale) is non-toxic to horses, the false dandelion otherwise known as Flatweed or Catsear is known to cause stringhalt.
Flatweed (Hypochaeris radicata or Hypochoeris radicata) while native to Europe, is very common all over the world. In the US it is often found in California, South Carolina and Washington State, while it is very common in Australia and New Zealand.
Flatweed is common in most lawns, large paddocks, waste and disturbed soils and areas prone to drought and poor soil nutrition. True Dandelion requires moist soils and tends to be found more in lawns and around areas that have plenty of water.
One quick way to tell the difference between Flatweed and True Dandelion is to check the flower stems. Dandelion has one stem, while Flatweed has branched flower stems with multiple flowers.
Clinical Signs Of Stringhalt
Horses with stringhalt suffer from a hindlimb lameness that could be described a little like “goose stepping”.
The high stepping hind leg gait is due to excessive hypermetria and hyperflexion of the stifle and hock. Sometimes, these horses may hit their belly with their hoof and ‘bunny hop’ along when walking.
Often clinical signs are worse at the walk and improve as speed increases. There are many racehorses that show signs of stringhalt at the walk and are still able to perform at high level and win races.
Backing the horse can noticeably increase clinical signs.
Stringhalt caused by consumption of Flatweed can result in other neuropathies such as laryngeal paralysis.
In very severe cases where segmental demyelination of nerves of the hind legs has caused peripheral neuropathy, neurogenic muscle degeneration may occur and we will see atrophy of hindlimb muscles such as the gaskin and/or rump.
How To Treat Stringhalt
The treatment of stringhalt depends entirely on what we suspect caused the problem in the first instance. Was it an injury? Did it “just happen?”, was the horse eating flatweed?
Treatment of stringhalt that is likely to be associated with an injury (i.e. it is often only affecting one hind leg) and not related to Flatweed toxicity may be able to be treated with surgery.
LATERAL DIGITAL EXTENSOR TENOTOMY
This surgery can be performed standing under local anaesthetic or in recumbancy under general anaesthetic. A portion of the lateral digital extensor tendon that crosses the lateral surface of the hock joint is removed.
Two incisions are made, the first is over the muscle belly of the lateral digital extensor just above the level of the point of the hock. The other is at the distal end of the lateral digital extensor tendon just before it joins the tendon of the long digital extensor.
The tendon is pulled out through the upper incision and about 15cm is removed.
After suturing the subcutaneous tissues and skin the area is bandaged.
Rehabilitation wise, it is important that the horse is kept active after the surgery. Plenty of trotting exercise can help to improve the success rate of this surgery.
Treatment of Stringhalt caused by Flatweed
- Use of anti-oxidants
- Vit B Complex
The first part of any treatment of Stringhalt is to remove the horses from the source of flatweed. You can put them in another paddock or yard/stable. The key is to ensure that there is no flatweed in sight.
It isn’t too important what you feed your horse, just make sure that there is no flatweed in hay.
You might need to decrease the amount of feed if your horse is affected badly enough that you can’t exercise them. You don’t want them bursting their seams!
Some veterinarians will advise to decontaminate by trying to ‘flush the system’ by giving laxatives. The idea behind this is to get as much of the weed out of the gastrointestinal system as fast as possible to prevent absorption.
We can do this by using Magnesium salts.
Because we don’t know the exact mechanism of toxicity, some will also recommend use of a mycotoxin binder. Evidence is lacking that mycotoxins are a factor in the disease process so we cannot recommend this.
Vitamin E and Vitamin C have antioxidant properties that may help to repair a peripheral neuropathy by scavenging free radicals.
Again, there is little evidence to suggest that this occurs.
A study by PJ Huntington in 1991 on the Use of Phenytoin to Treat Horses with Australian Stringhalt showed that 15 mg/kg of phenytoin given with feed every 12 hrs for 2 weeks helped to improve clinical signs of stringhalt.
Phenytoin is an anti-epileptic medication (centrally acting anti-convulsant) that hyperpolarises the nerve membrane so that the potential threshold is increased and decreases the action potential peak thereby reducing clinical signs i.e. firing of the nerves is dampened.
Vitamin B Complex And Magnesium
In humans, peripheral neuropathies can be due to a deficiency in Vitamin B, in particular thiamine (B1). There is no evidence in horses that this treatment is of benefit. If clinical signs do improve it is likely due to improving clinical signs, not improvement of the peripheral neuropathy.
For personalised advice regarding a horse with stringhalt ask a vet a question here.
Prevention of Stringhalt
The prognosis of recovery for horses affected with stringhalt is fair. Full recovery can occur, but it can take anywhere from 2 weeks to 2 years.
For this reason, prevention is better than cure. It is very important to assess your paddocks for signs of flatweed and remove this immediately. Plan a regular inspection especially after periods of rain.
If your horse has experienced stringhalt, tell us in the comments below. How long did it take for them to recover?