Tying Up

When a horse's muscles become painful, stiff and unable to work normally

“Tying up” is the commonly used name for an episode in which a horse develops painful muscle damage, usually associated with exercise.

You may also hear your vet describe it as exertional rhabdomyolysis (ER). In everyday language, this means that muscle cells have been damaged during or around exercise and their normal contents begin to leak into the bloodstream.

An affected horse may suddenly become reluctant to move, develop hard or painful muscles, sweat excessively or appear distressed. Some episodes are relatively mild, while severe cases can be extremely painful and potentially serious.

If you think your horse may be tying up, stop exercising and contact your vet. Do not try to make the horse “walk it off”.

What is actually happening?

Muscles work by repeatedly contracting and relaxing. To do this successfully they need energy, normal electrolyte balance and properly functioning muscle cells.

During a tying-up episode, some of those muscle cells become damaged. The muscles can become painful, inflamed and unable to contract and relax normally.

The large muscles over the hindquarters and back are commonly affected, although muscle damage is not necessarily confined to these areas.

This is why a horse that was working normally can suddenly feel extremely stiff or become unwilling to continue moving.

The term rhabdomyolysis sounds complicated, but essentially means breakdown or damage of skeletal muscle cells.

Importantly, tying up is not always caused by the same underlying problem. Two horses can show very similar signs while having quite different reasons for developing them.

What might an owner notice?

Signs vary considerably according to the severity of the episode.

You may notice:

• sudden stiffness during or shortly after exercise
• reluctance or refusal to move forward
• a change in the horse's normal movement
• shortened, guarded or uncomfortable-looking movement
• hard, tense or painful muscles, particularly over the hindquarters
• excessive sweating that seems out of proportion to the work being performed
• rapid breathing
• increased heart rate
• distress, anxiety or agitation
• trembling or muscle fasciculations
• reluctance to turn
• difficulty moving the hindquarters normally
• standing in an unusual or uncomfortable posture
• dark brown, reddish or coffee-coloured urine in more severe cases.

Not every horse will show all of these signs.

A mild episode can sometimes be mistaken for ordinary stiffness or poor performance, while a severe episode may be very obvious.

Why can the urine become dark?

Severe muscle damage can release a muscle protein called myoglobin into the bloodstream.

The kidneys remove myoglobin from the blood and it can then pass into the urine, giving it a dark red-brown or coffee-like appearance.

This is called myoglobinuria.

It is an important warning sign because substantial muscle damage has occurred and the kidneys may also be placed under considerable strain.

Dark urine associated with suspected tying up requires prompt veterinary attention.

Terms you may hear from your vet

Exertional rhabdomyolysis – ER

This is the veterinary term often used for a tying-up episode associated with exercise.

In simple terms: muscle cells have been damaged and are breaking down.

Sporadic exertional rhabdomyolysis

“Sporadic” means that the episode appears to be an isolated event rather than part of an established recurring muscle disorder.

It may be associated with circumstances such as unusually strenuous exercise, exercise beyond the horse's current fitness, nutritional imbalance, illness or other contributing factors.

Recurrent exertional rhabdomyolysis – RER

“Recurrent” means that episodes happen repeatedly.

RER is recognised particularly in some Thoroughbreds and other horses, and affected horses can have an underlying tendency for abnormal regulation of muscle contraction.

In everyday language: the horse is predisposed to repeated episodes rather than simply having worked too hard on one occasion.

Excitement and stress can be important contributing factors in susceptible horses.

PSSM – Polysaccharide Storage Myopathy

PSSM is a muscle disorder involving the way energy is stored and/or used within muscle.

There are different forms and causes of muscle disease that have historically been grouped under the PSSM terminology, so diagnosis is important rather than assuming that every horse that ties up has PSSM.

In everyday language: some affected horses have an underlying problem with how their muscles handle stored energy, which can contribute to muscle pain and exercise problems.

Myopathy

“Myopathy” simply means a disease or disorder affecting muscle.

It describes where the problem is rather than necessarily telling you its exact cause.

What are CK and AST?

If your vet suspects muscle damage, they may take a blood sample and talk about the horse's muscle enzymes.

Two names owners commonly hear are CK and AST.

CK – Creatine Kinase

CK is found in muscle cells.

When those cells are damaged, CK can escape into the bloodstream and the measured level can rise.

A raised CK therefore gives your vet useful evidence that muscle damage has occurred.

AST – Aspartate Aminotransferase

AST can also increase following muscle damage, although it behaves differently from CK and is not found exclusively in muscle.

Your vet may look at CK and AST together, along with the timing of the episode, examination findings and other tests, to help understand what has happened.

So when an owner is told that their horse has “raised muscle enzymes”, it does not mean that the enzymes themselves are causing the problem. They are useful markers that can indicate muscle-cell damage.

Why does tying up happen?

There isn't one single cause.

An isolated episode may be associated with factors including:

• strenuous or unaccustomed exercise
• exercising beyond the horse's current level of fitness
• sudden changes in workload
• inappropriate nutritional management
• electrolyte and fluid losses
• illness or other physiological stresses.

Repeated episodes may make your vet consider whether there is an underlying muscle disorder or individual predisposition.

The circumstances surrounding an episode matter enormously. Your vet may therefore want to know about the horse's exercise, fitness, feeding, turnout, previous episodes, temperament and what happened immediately before the problem developed.

Is tying up simply caused by lactic acid?

This is a common misconception.

Tying up was historically associated with ideas about lactic acid accumulating in the muscles, but equine exertional rhabdomyolysis is not simply a case of lactic acid becoming trapped in the muscles.

Modern understanding recognises muscle-cell damage and a range of possible underlying mechanisms and risk factors.

That is one reason why identifying what is happening in the individual horse is much more useful than treating every tying-up episode as though it has the same cause.

What should I do if my horse ties up?

If a horse suddenly develops signs consistent with tying up:

Stop exercising the horse and contact your vet.

Do not force the horse to continue walking in an attempt to loosen the muscles.

Depending on the circumstances and severity, your vet may assess hydration, muscle pain, cardiovascular status and other clinical signs and may take blood and/or urine samples.

Treatment will depend on the individual case.

A severely affected horse may require considerably more veterinary support than a horse experiencing a mild episode.

When is it particularly urgent?

Seek veterinary advice promptly whenever tying up is suspected, and particularly if the horse:

• is extremely painful or distressed
• is very reluctant to move
• is sweating heavily
• has a markedly increased breathing or heart rate
• is weak or unstable
• has dark red or brown urine
• appears dehydrated
• has severe muscle stiffness
• has experienced previous episodes.

The outward appearance of the horse does not always tell you precisely how much muscle damage has occurred.

After an episode

Recovery and return to exercise should be guided by your vet, particularly following a significant episode.

The fact that a horse appears more comfortable does not necessarily mean that the affected muscle cells have completely recovered.

Depending on the case, your vet may recommend repeat blood testing before normal exercise resumes.

For horses that experience repeated episodes, investigation of the underlying cause becomes particularly important.

Management may then involve a combination of:

• an appropriate exercise programme
• consistent daily routine
• suitable turnout
• appropriate dietary energy sources
• balancing vitamins and minerals
• adequate salt and electrolyte provision
• careful management of stress or excitement where relevant
• investigation for an underlying muscle disorder.

The correct approach depends upon why that particular horse is tying up.

Feeding and muscle health

Nutrition cannot replace veterinary investigation of a horse that ties up.

However, appropriate nutrition is an important part of long-term muscle management.

The horse should receive a balanced diet appropriate for its workload, body condition and individual needs. Particular attention may be given to:

• total dietary energy
• the amount and type of starch and sugar being fed
• adequate good-quality protein
• vitamin and mineral balance
• antioxidant nutrients
• salt and electrolyte replacement
• access to water.

Horses with particular diagnosed muscle disorders may require more specific dietary management, which should be planned with the vet and an appropriately qualified equine nutrition professional.

Electrolytes – important, but not the whole story

Muscle contraction depends upon minerals including sodium, potassium, chloride, calcium and magnesium.

A working horse loses water and electrolytes through sweat, and those losses can become substantial during prolonged exercise, hot weather or heavy sweating.

Replacing appropriate electrolyte losses can therefore be an important part of supporting normal hydration, nerve and muscle function.

However, electrolyte supplementation should not be presented as a treatment for tying up itself.

A horse experiencing recurrent episodes needs the underlying reason investigated rather than simply receiving increasing quantities of electrolytes.

Can tying up be prevented?

Not every episode can be prevented, particularly where an underlying muscle disorder exists.

Risk may nevertheless be reduced through appropriate management.

Useful principles include maintaining:

• a consistent exercise routine
• fitness appropriate to the work being asked
• gradual changes in workload
• appropriate warm-up and cool-down
• suitable nutrition for the individual horse
• adequate hydration
• appropriate salt and electrolyte provision
• regular turnout where suitable
• careful management of horses known to become highly excited or stressed.

For a horse with recurrent episodes, an individual management programme based on veterinary investigation is far more valuable than a generic “tying-up diet”.

The important distinction

Tying up describes what is happening to the horse's muscles. It does not necessarily tell us why it is happening.

One horse may experience an isolated episode after unusual circumstances.

Another may have a recurring susceptibility.

Another may have an identifiable underlying muscle disorder.

Recognising that distinction helps owners understand why veterinary investigation can be important, particularly when episodes recur.

Suggested Graphics

Graphic 1 – Hero Graphic

“Tying Up – When Muscles Become Painful and Damaged”

Visual concept:
A high-quality side view of a horse with subtle anatomical highlighting over the major muscles of the back and hindquarters. Avoid making the horse appear collapsed or dramatically distressed. The graphic should communicate muscular involvement rather than suggest that tying up affects only one specific muscle.

Headline:
TYING UP

Supporting line:
Also called exertional rhabdomyolysis – painful damage to muscle cells associated with exercise.

Three short call-outs:

Sudden stiffness
The horse may become reluctant to continue moving.

Painful muscles
Large muscles of the back and hindquarters are commonly affected.

Stop exercise
Suspected tying up requires veterinary advice – don't try to “walk it off”.

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Owner education from JCG Supplements
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Graphic 2 – “Veterinary Words Explained”

Designed specifically as a useful standalone educational graphic that an owner could save, print or share.

TYING UP – THE WORDS YOUR VET MAY USE

Exertional rhabdomyolysis (ER)
Muscle cells have become damaged in association with exercise.

Recurrent exertional rhabdomyolysis (RER)
The horse has a tendency to experience repeated episodes.

PSSM
A term associated with disorders affecting how energy is stored or handled within muscle.

Myopathy
A disease or disorder affecting muscle.

Raised CK / AST
Blood-test findings that can help your vet identify and assess muscle damage.

Myoglobinuria
Muscle protein entering the urine, which can make it appear dark red-brown.

Key message:
Tying up describes muscle damage – the underlying reason can differ between horses.

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Educational information for horse owners – suspected tying up requires veterinary advice.

Graphic 3 – “Recognise the Signs”

A clean illustrated horse surrounded by six concise signs.

COULD YOUR HORSE BE TYING UP?

Look for:

• sudden stiffness
• reluctance to move
• hard or painful hindquarter muscles
• excessive sweating
• rapid breathing or distress
• dark red-brown urine in severe cases

WHAT SHOULD YOU DO?

STOP EXERCISE • CONTACT YOUR VET • DON'T FORCE THE HORSE TO WALK

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Practical equine health information for owners
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Important

This information is intended to help horse owners understand tying up and terminology they may hear from their vet. It is not intended to diagnose an individual horse or replace veterinary examination and advice.

A horse showing signs of tying up should stop exercise and receive veterinary advice.