Tying-Up in Horses

What tying-up in horses is, the signs to watch for, why you should keep the horse still and phone your vet, and how to lower the risk.

Quick Answer

Tying-up in horses, also called exertional rhabdomyolysis or azoturia, is a painful muscle condition that usually happens during or shortly after exercise.
UK vet sources treat it as an emergency, so if you suspect an episode, stop work, keep the horse still and phone your vet straight away.
Signs include a stiff gait, reluctance to move, hard muscles, heavy sweating and dark red-brown urine.
Severe cases can damage the kidneys and lead to collapse, and the pain can be mistaken for colic.
Do not move the horse, and do not give any medicine unless your vet tells you to, because treatment is decided by your vet.

Tying-up in horses is the common name for a disturbance in how the muscles work. It causes painful cramps and muscle damage. Other names include azoturia, set-fast and Monday morning disease.

A horse might tie up just once, but some horses are prone to repeated episodes. This guide explains the signs, what to do while you wait for your vet and how vets manage it.

Woman in a blue jacket leading two chestnut horses into a red barn – tying-up in horses usually happens during or shortly after exercise

What is tying-up in horses?

Vets call it exertional rhabdomyolysis, often shortened to ERM. It is not only a racehorse problem. It is seen in all athletic disciplines, and it can even happen while hacking.

The MSD Veterinary Manual, a US reference, says the term now covers several conditions that look similar but have different causes. A 2011 article from the University of Edinburgh vet school says cases are quite common, yet exactly how the disease happens is still poorly understood.

Signs range from mild, such as a variable drop in performance, to severe. In rare cases, collapse and death can occur.

Why tying-up in horses happens

There is often no single cause. UK sources describe a few patterns.

Exercise and feeding out of balance

It is most often seen when exercise and feeding are out of balance. One example is keeping a high-energy diet while suddenly cutting down exercise.

Reduced work might be due to the season, illness, injury or a holiday. In these cases, calories should be reduced too.

Over-exertion or something toxic

A one-off episode can sometimes follow over-exertion. It can also follow eating something toxic, such as sycamore seeds or seedlings.

Man leading a brown-and-white horse along a quiet rural road – a careful routine of work and rest helps manage tying-up in horses

Repeated episodes

Repeated episodes appear to be a syndrome with both genetic and environmental elements. This is called recurrent exertional rhabdomyolysis (RER).

The gene or genes behind it have not yet been identified. There is currently no cure, although many horses can continue to perform well if managed appropriately.

A genetic muscle condition

One genetic disorder, type 1 polysaccharide storage myopathy (PSSM1), is common in the UK. However, most UK horses that tie up do not have this mutation. Your vet can advise on tests.

Temperament and season

Research suggests horses with a more excitable temperament are more likely to have an episode. Some mares develop the condition when in season.

Signs of tying-up

Signs usually start during or just after exercise. Look out for:

Lack of impulsion, or unwillingness to move
A stiff gait, particularly in the hind legs
Muscles that are suddenly hard or trembling, especially over the hindquarters
A high heart or breathing rate
Far more sweating than the exercise warrants
A horse that seems rooted to the spot, or lies down and cannot or will not get up
Dark red-brown urine

The dark urine is not blood. It is caused by myoglobin, a muscle pigment released from damaged muscle. At high levels it can damage the kidneys.

In severe cases the pain can be extreme and may be confused with colic. See Signs of Colic in Horses for how colic looks.

Do not confuse it with atypical myopathy

Atypical myopathy is a separate, sycamore-related muscle disease. Its signs overlap, including dark urine, weakness and reluctance to walk, and horses can deteriorate within 6 to 12 hours. The BHS says to seek urgent veterinary help if you are concerned.

Emergency: Contact a Vet Immediately If…

Your horse is stiff or reluctant to move during or after exercise.
The muscles feel hard or painful, especially over the hindquarters.
Your horse is sweating heavily for no clear reason.
The urine is dark red-brown.
Your horse lies down and is unwilling or unable to rise.
The horse seems to have colic-like pain together with stiff muscles.

Stop work, keep the horse still and phone your vet or the nearest out-of-hours emergency vet straight away.

When to Contact Your Vet

As soon as you suspect an episode. XLEquine calls it a veterinary emergency.
If your horse has tied up before. Your vet may recommend tests to find the underlying cause.
If you notice an unexplained drop in performance after exercise.

Severe episodes can damage the kidneys, and lead to collapse and death. Do not wait to see whether the horse improves.

What to do while you wait for the vet

Phone your vet first. Then follow the cautious advice below, and any instructions your vet gives you.

Do

Stop work and keep the horse still, to reduce further muscle damage.
Keep the horse calm. In cold weather, a rug can keep it warm.
Offer water.
Have the horse's passport to hand for your vet.

Do not

Do not move the affected horse, or make it walk. If it is somewhere unsafe, ask your vet first.
Do not give any medicine unless your vet tells you to.

The US MSD Veterinary Manual says to move the horse to a stall. XLEquine, a UK vet network, says to keep the horse still and not to move it, so follow your vet.

How vets diagnose and treat tying-up in horses

Often a vet will confirm the diagnosis with a blood sample. Three muscle enzymes (CK, AST and LDH) are raised in tying-up, and the results show how much muscle is damaged. In severe cases, kidney function is also checked with repeat blood tests.

If it has happened before, your vet may suggest a muscle biopsy or other tests. One type of PSSM can be diagnosed from a hair sample.

Treatment depends on severity. It usually aims to reduce pain and inflammation, restore fluid balance and protect the kidneys. Your vet may give painkillers and fluids, by stomach tube or into a vein. Serious cases may be hospitalised for 24-hour care.

Recovery often involves box rest, then small paddock turnout or short hand-walking until blood enzymes return to normal. Full recovery and a return to full work may take several weeks.

The horse's passport food-chain declaration determines which medicines can be given and what records must be kept. If you compete, check the current rules with your vet and your governing body.

Preventing tying-up in horses

Management cannot guarantee a horse will never tie up again, but UK sources suggest these steps for prone horses:

Feed a balanced diet with good-quality hay, and reduce calories when work drops.
Choose a diet low in sugar and starch, replacing those calories with fat. How this helps is unclear.
Exercise regularly, with plenty of time to warm up and cool down.
Avoid box rest if you can, and bring a horse back into work carefully after a break.
Give plenty of turnout, but avoid lush grazing as part of the diet.
Keep a regular routine and reduce stress around exercise, stabling, turnout and transport.
Take extra care when turnout and exercise are reduced, such as in winter.

Your Horse says a vet might recommend preventive medication for some prone horses. For mares that tie up in season, ask your vet about managing oestrus.

Despite the best management, some horses struggle to keep up an athletic career. For other causes of stiffness, see Why Is My Horse Lame?

How Pet Med Direct Can Help

Tying-up is a situation for your vet first. Please phone your vet straight away, before you buy or give anything.

If your vet prescribes a medicine, how pet prescriptions work explains the process. Prescription-only medicines (POM-V) are supplied solely against a valid prescription from the horse's own vet. You can also browse our equine range.

Some pet medicines require a valid veterinary prescription. Pet Med Direct can only supply prescription medicines after the prescription has been checked. Always follow your vet's advice and the directions on the medicine label.

Frequently Asked Questions

What is tying-up?

It is the common name for exertional rhabdomyolysis, a painful muscle condition with cramps and muscle damage. It usually happens during or shortly after exercise.

Should I walk my horse if it ties up?

No. XLEquine advises keeping the horse still to reduce further muscle damage, and not moving an affected horse. Phone your vet and ask before you move it.

Why is my horse's urine dark after exercise?

It can be myoglobin from damaged muscle, not blood. Treat dark red-brown urine as an emergency and phone your vet.

Is tying-up the same as colic?

No, but severe tying-up pain can be mistaken for colic. Either way, you need your vet.

Can a horse recover from tying-up?

Many horses can continue to perform well if managed appropriately, although severe cases can be fatal. Full recovery from an episode may take several weeks. There is currently no cure for the recurrent form.

Does cold water cause tying-up?

The British Horseracing Authority's hot weather policy says applying cold water to a hot horse does not cause shock, muscle damage or tying-up. If your horse is overheating, see Heat Stress in Horses.

Related Equine Health Guides

Sources and Further Reading

This article was researched from the sources listed above. It is general information for horse owners and is not a substitute for advice from your own vet.

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This article is for informational purposes only and does not constitute veterinary advice.
If you are concerned about your horse’s health, please consult a qualified veterinarian.