Stringhalt in Horses (Equine Reflex Hypertonia)
- Horse Education Online
- Jul 13
- 9 min read
Updated: Jul 28
Causes, Diagnosis, Treatment, and Prognosis of this Unusual Neuromuscular Disorder
A horse suddenly jerks one hind leg high toward its belly with every step. The movement looks exaggerated, involuntary, and almost as though the horse is startled by its own limb. While this unusual gait can be alarming, it is a well-recognized neurological condition known as stringhalt.
Stringhalt is an uncommon neuromuscular disorder characterized by sudden, exaggerated flexion of one or both hind limbs during movement. Depending on its severity, it may appear as nothing more than a slight "hitch" in the horse's stride or become so dramatic that the hoof nearly strikes the abdomen.
Unlike many lameness conditions, stringhalt is not caused by pain within a joint. Instead, it results from abnormal nerve function affecting the muscles responsible for flexing the hind limb.
Learn more about the Equine Nervous System, and use our Neuro Screen & Localization Assistant to see which symptoms correlate with different neurological diseases.
What is Stringhalt?
Stringhalt is a neurological movement disorder in which the hind limb suddenly flexes upward far more than normal during movement. The excessive flexion happens involuntarily because the nerves controlling the muscles of the limb are not functioning normally.
The condition is classified by UC Davis as equine reflex hypertonia, meaning the normal reflexes that control muscle movement have become overactive.
The abnormal movement is usually easiest to see:
At the walk
During the first few steps after standing
While backing up
During tight turns
Occasionally during the trot
Some horses only show subtle abnormalities, while others exhibit dramatic, repetitive lifting of the hind limb.
The condition may affect one hind leg (unilateral) or both hind legs (bilateral).
Did You Know? Stringhalt is one of the few equine gait abnormalities that often becomes more obvious when a horse backs up rather than when moving forward. This simple observation can provide an important diagnostic clue during a veterinary examination.
What Does Stringhalt Look Like?
The severity of stringhalt varies tremendously between horses.
Some horses simply appear to "snatch" the hind limb upward during walking. Others may raise the limb so high that the hoof nearly touches the belly before rapidly returning it to the ground. Watch the video below to see it in action.
Common signs include:
Clinical Sign | Appearance |
Sudden upward jerk of the hind limb | Excessive flexion of the hock and stifle |
Most noticeable at the walk | Less obvious at faster gaits |
Worse after standing | Often improves slightly after warming up |
Increased during backing | Classic diagnostic feature |
One or both hind limbs affected | May begin in one limb and progress |
Variable severity | Mild hitch to extreme hyperflexion |
Muscle wasting | May develop in chronic cases |
Merck Veterinary Manual describes severe cases in which the limb is drawn sharply upward before being forcefully placed back onto the ground.
Stringhalt vs. Shivers
Because both disorders affect the hind limbs, stringhalt and shivers are frequently confused.
Although they may appear similar at first glance, they involve very different movement patterns.
Stringhalt
Sudden exaggerated flexion during forward movement
Limb rapidly snaps upward and back down
Most noticeable while walking
Usually consistent with every stride
Difficulty lifting the hind limb normally
Limb held elevated and often abducted (outward)
Trembling while attempting to flex the leg
Most noticeable when backing or picking up the foot
A 2022 review found that horses with stringhalt typically show exaggerated flexion without abduction, helping veterinarians distinguish it from shivers.
If you'd like to learn more about other neurological disorders, you may also enjoy our articles on Shivers in Horses, Ataxia in Horses, Wobbler Syndrome, and Sidewinder Syndrome.
Did You Know? Many neurological disorders can alter a horse's gait, but careful observation of how the limb moves is often more valuable than simply noting that the horse is "walking funny."
What Causes Stringhalt?
Veterinarians recognize two major forms of the disease: Idiopathic and Pasture-Associated Stringhalt.
Idiopathic Stringhalt
Idiopathic simply means the exact cause is unknown.
These horses develop stringhalt without any obvious toxic plant exposure or identifiable injury.
Research suggests the underlying problem involves dysfunction of the peripheral nerves controlling the hind limb muscles.
Studies have identified abnormalities affecting:
Sciatic nerve
Tibial nerve
Common fibular nerve (peroneal nerve)
Damage to these nerves alters the normal communication between the nervous system and the muscles, producing the exaggerated flexion reflex characteristic of the disease.
Pasture-Associated (Australian) Stringhalt
The second form is far more interesting from a scientific perspective.
Pasture-associated stringhalt has repeatedly been linked to horses grazing Hypochaeris radicata, commonly known as:
Flatweed
False dandelion
Catsear
The disease is most commonly reported during:
Drought
Overgrazed pastures
Poor-quality forage conditions
When desirable grasses become scarce, horses consume larger amounts of weeds, increasing the likelihood of toxic exposure.
Outbreaks have been reported in:
Australia
New Zealand
South America
North America
Experimental feeding studies have even reproduced the disease under controlled conditions.
Other Reported Associations
Researchers have also suggested possible links with:
Possible Cause | Evidence |
Flatweed (Hypochaeris radicata) | Strongest association |
Sweet pea toxicity (Lathyrus spp.) | Rare reported cause |
Peripheral nerve injury | Supported by pathology |
Trauma | Occasionally suspected |
Unknown causes | Common in idiopathic cases |
What Happens Inside the Body?
Unlike joint disease or tendon injuries, stringhalt primarily affects the nervous system.
The pathology centers on damage to the long peripheral nerves supplying the hind limbs.
Researchers have described:
Peripheral neuropathy
Distal axon degeneration
Abnormal reflex pathways
Muscle denervation
Secondary muscle atrophy
Because the nerves supplying the hind limbs are among the longest in the body, they appear especially vulnerable to damage. When nerve fibers become injured, the muscles no longer receive normal signals, resulting in abnormal reflex activity.
In chronic cases, the affected muscles may begin to shrink due to loss of normal nerve stimulation.
Did You Know? The muscles themselves are often not the primary problem. Instead, damaged nerves cause healthy muscles to receive abnormal instructions, producing the exaggerated movement seen in stringhalt.
Diagnosing Stringhalt
Diagnosis begins with a thorough history and physical examination.
Veterinarians spend considerable time simply watching the horse move.
Common components of the examination include:
Examination | Purpose |
Walking in hand | Evaluate abnormal gait |
Backing | Often exaggerates signs |
Tight circles | Helps identify subtle cases |
Neurological examination | Rule out spinal cord disease |
Lameness examination | Differentiate orthopedic pain |
Pasture evaluation | Look for toxic weeds |
Bloodwork | Investigate underlying disease |
Electromyography | Assess nerve function in selected cases |
Muscle biopsy | Occasionally confirms denervation |
No single laboratory test confirms stringhalt.
Instead, veterinarians combine movement analysis, neurological findings, and the horse's history to reach a diagnosis.
Conditions That Can Mimic Stringhalt
Because abnormal hind limb movement has many possible causes, veterinarians must rule out several other disorders.
These include:
Fibrotic Myopathy
Stifle disease
Peripheral nerve injuries
Several of these conditions have very different treatments, making an accurate diagnosis essential.
Learn to Recognize Lameness and Gait Faults
Stringhalt is one of many gait abnormalities that can affect a horse's movement. Being able to recognize the difference between gait faults caused by neurological disease, lameness, or conformational problems is an important skill for every horse owner and equine professional. To help you build that knowledge, Horse Education Online offers a downloadable Lameness Flashcard Study Set and a downloadable Gait Fault Flashcard Study Set. These printable flashcards illustrate and explain common lamenesses and gait abnormalities, making it easy to study at home, prepare for certifications, or sharpen your observational skills in the barn. You may also enroll in our Online Equine Lameness Certification Program for an even more in-depth dive.
Treatment
Treatment depends largely on the underlying cause.
Treating Pasture-Associated Stringhalt
If toxic pasture plants are suspected, immediate removal from the pasture is the first priority.
Management typically includes:
Treatment | Purpose |
Remove from affected pasture | Prevent continued exposure |
Feed good-quality hay | Replace contaminated forage |
Weed control | Prevent recurrence |
Controlled exercise | Maintain muscle condition |
Veterinary monitoring | Track improvement |
Many horses gradually improve over several weeks or months.
However, severe cases may require much longer recovery periods, and some horses never return completely to normal.
Treating Idiopathic Stringhalt
Because the exact cause remains unknown, treatment is less predictable.
Possible options include:
Observation in mild cases
Controlled exercise programs
Physical rehabilitation
Medical therapy
Surgery in selected horses
No medication has consistently proven effective.
Some individual case reports describe improvement following treatment with phenytoin sodium, sometimes combined with vitamin supplementation, but scientific evidence remains limited.
Surgical Treatment
When conservative management fails, some veterinarians may recommend surgery.
The most commonly reported procedure is:
Lateral digital extensor tenectomy with partial myectomy
This surgery removes part of the tendon and muscle believed to contribute to the exaggerated movement.
Published reports have described improvement in some horses, but outcomes vary considerably, and surgery cannot guarantee complete resolution.
Did You Know? Some horses with pasture-associated stringhalt recover almost completely once removed from the toxic pasture, while others require many months of rehabilitation. Early recognition greatly improves the chances of recovery.
Prognosis
The outlook depends on:
The underlying cause
Severity of neurological damage
Duration of clinical signs
Presence of muscle atrophy
Type | Prognosis |
Mild pasture-associated | Fair to good |
Severe pasture-associated | Guarded |
Idiopathic | Variable |
Chronic with muscle wasting | More guarded |
Severe disabling disease | Poor |
Many horses return to comfortable riding careers.
Others continue to display mild gait abnormalities throughout life.
In severe cases where the horse can no longer move safely or comfortably, euthanasia may unfortunately become the most humane option.
Can Stringhalt Be Prevented?
Not every case can be prevented, particularly idiopathic stringhalt.
However, horse owners can reduce the risk of pasture-associated disease by:
Avoiding overgrazed paddocks
Providing adequate forage during drought
Controlling flatweed (Hypochaeris radicata)
Monitoring pasture quality regularly
Introducing supplemental hay before weeds become the primary food source
Routine pasture management remains one of the most effective preventive measures.
Key Takeaways
Stringhalt is an uncommon neuromuscular disorder characterized by exaggerated flexion of one or both hind limbs during movement. Although its appearance can be dramatic, not every case carries a poor prognosis. Horses affected by pasture-associated stringhalt often improve after removal from toxic grazing conditions, while idiopathic cases tend to be more variable and may require long-term management.
Because stringhalt resembles several orthopedic and neurological disorders, a complete veterinary examination is essential before beginning treatment. Careful observation of the horse's gait, a thorough neurological assessment, and consideration of the horse's environment all play important roles in reaching the correct diagnosis.
Frequently Asked Questions
What is stringhalt in horses?
Stringhalt is an uncommon neuromuscular disorder that causes one or both hind limbs to flex upward suddenly and excessively during movement.
The movement is involuntary and results from abnormal nerve function affecting the muscles that flex the hind limb. The equine nervous system guide explains how nerve signals control movement and coordination.
What does stringhalt look like?
A horse with stringhalt may suddenly jerk or snatch a hind leg upward while walking. In severe cases, the hoof may rise close to the abdomen before being placed forcefully back on the ground.
Signs are often most noticeable at the walk, during the first steps after standing, while backing and during tight turns.
Can stringhalt affect only one hind leg?
Yes. Stringhalt may affect one hind limb or both hind limbs.
Some horses remain affected on one side, while others may initially show signs in one limb before the condition progresses.
What causes stringhalt in horses?
Veterinarians recognize two main forms: idiopathic stringhalt and pasture-associated stringhalt.
The exact cause of idiopathic stringhalt is unknown, although peripheral nerve dysfunction is involved. Pasture-associated stringhalt has been linked most strongly to grazing flatweed, also called false dandelion or catsear.
What is pasture-associated stringhalt?
Pasture-associated stringhalt develops after exposure to toxic pasture conditions, particularly where horses consume large amounts of Hypochaeris radicata.
Cases are most commonly reported during drought, overgrazing and poor-quality forage conditions. Providing suitable forage and managing pasture quality are therefore important parts of prevention.
Is stringhalt the same as shivers?
No. Stringhalt causes the hind limb to snap rapidly upward and back down during forward movement.
Shivers more commonly causes difficulty lifting the limb, trembling and outward movement of the leg, especially during backing or when the foot is picked up. Careful gait observation is important because several neurologic and orthopedic disorders can appear similar.
How is stringhalt diagnosed?
Diagnosis is based on the horse’s gait, medical history, neurologic examination, lameness examination and possible pasture exposure.
Veterinarians may watch the horse walk, back and perform tight circles. Bloodwork, electromyography or muscle biopsy may be used in selected cases, but no single laboratory test confirms every case. The Equine Neuro Screen and Localization Assistant can help owners organize observations before contacting their veterinarian.
How is stringhalt treated?
Treatment depends on the underlying form.
When pasture-associated stringhalt is suspected, the horse should be removed from the affected pasture and provided with good-quality hay. Weed control, controlled exercise and veterinary monitoring may also be recommended.
Idiopathic cases may be managed with observation, controlled exercise, physical rehabilitation, medical therapy or surgery in selected horses. No medication has consistently proven effective.
Can a horse recover from stringhalt?
Many horses with mild pasture-associated stringhalt improve after removal from the contaminated pasture, although recovery may take weeks or months.
The prognosis for idiopathic stringhalt is more variable. Severe cases, chronic disease and muscle wasting carry a more guarded outlook. Owners can use Horse Tracker to document gait changes, pasture exposure, muscle loss, veterinary findings and response to treatment.
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