Exertional Rhabdomyolysis in Horses: Tying-Up Signs and Recovery
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By Dr Duncan Houston
A horse that becomes stiff, sweaty and unwilling to move during or after exercise may be tying-up. The veterinary term, exertional rhabdomyolysis, describes damage to muscle cells associated with exercise. It ranges from relatively mild injury to a serious illness requiring hospital care.
Stop the session and take the signs seriously. Trying to walk the stiffness out can worsen muscle damage, and repeated episodes need investigation rather than a succession of different feed supplements.
Quick Answer
Stop exercise and call your veterinarian if a horse develops painful, firm muscles, marked stiffness, sweating or reluctance to move. Do not force walking or give medication without advice. Treatment and future exercise depend on the severity and underlying cause, which may be a one-off exertional problem or a recurrent muscle disorder.
Why tying-up happens
Sporadic episodes may follow work that exceeds the horse’s fitness, particularly with additional stressors such as heat, illness or an unsuitable training programme. Recurrent exertional rhabdomyolysis is more complex: some horses have an underlying susceptibility despite apparently reasonable workloads. The MSD Veterinary Manual’s exertional myopathy guidance distinguishes these patterns because their longer-term management differs.
Polysaccharide storage myopathy type 1, or PSSM1, is one possible cause of muscle disease. It is associated with a known GYS1 genetic variant, and a validated test is available. It is not the explanation for every horse that ties-up. Other muscle conditions, electrolyte disturbances and training-related problems need consideration.
Recognising an episode
| Finding | Why it matters | What to do |
|---|---|---|
| Stiff hindquarters, sweating and painful muscles after work | Possible exertional muscle injury | Stop and call the veterinarian |
| Dark red-brown urine | May indicate muscle pigment or another urinary problem | Report urgently; colour alone cannot diagnose the cause |
| Severe pain, weakness, collapse or overheating | Potentially serious systemic complications | Request emergency assessment |
| Repeated mild stiffness or poor performance | Possible recurrent myopathy or an alternative problem | Arrange investigation before increasing work |
Colic, laminitis, lameness, heat illness and neurological disease can also make a horse reluctant to move or sweaty. A normal-looking urine sample does not exclude tying-up. Examination and testing are needed to separate these possibilities.
When is it an emergency?
Severe pain, inability to move safely, dark urine, marked weakness, collapse or signs of heat illness require urgent veterinary help. Keep the horse where it is safe; do not force it back to the stable. Remove tack if safe, allow water and follow instructions about cooling. Do not load a horse that cannot move comfortably without veterinary advice about stabilisation and transport.
Diagnosis and immediate treatment
Blood tests measure muscle enzymes such as creatine kinase, often called CK, and AST. Their timing and trends help interpret the injury; the numbers do not identify every underlying cause. The veterinarian may also check hydration, kidney function, electrolytes and urine, because severe muscle injury can release pigment that threatens the kidneys.
Treatment can include veterinary pain relief and fluid support according to severity. Drugs that are suitable for one horse may be inappropriate for a dehydrated horse with kidney concerns. Rest is needed during the acute injury, but its duration and the return to exercise depend on clinical recovery and follow-up results. See the MSD owner guide to muscle disorders for the broader diagnostic context.
Investigating repeated episodes
Provide training records, feed labels, exercise timing, recent rest days and details of previous episodes. The veterinarian may recommend genetic testing, further blood tests or muscle biopsy in selected cases. The UC Davis Veterinary Genetics Laboratory explains what its PSSM1 test can establish. A negative PSSM1 result does not rule out other muscle disease.
Be cautious about commercial panels marketed as diagnosing PSSM2. UC Davis guidance on PSSM explains the limitations of unvalidated variants. A label from such a panel should not replace clinical investigation or determine breeding and purchasing decisions on its own.
A practical recovery plan
- Follow the acute treatment and movement instructions, including when to call if pain or urine changes worsen.
- Keep a record of appetite, drinking, urination, comfort and medicines.
- Attend repeat assessments and obtain clearance before resuming ridden or driven work.
- Review the whole ration with your veterinarian or nutritionist. Energy source, total intake and mineral balance should match the diagnosed condition.
- Reintroduce exercise progressively and keep the longer-term routine consistent with the specific muscle disorder.
- Reassess promptly after any recurrence instead of pushing through a training session.
Common mistakes to avoid
- Forcing a painful horse to walk to “loosen up”.
- Assuming all tying-up is caused by lactic acid or one vitamin deficiency.
- Adding selenium or multiple muscle supplements without checking the complete ration.
- Starting a high-fat or restrictive diet without an individual nutritional plan.
- Returning to full work simply because the horse looks normal the next morning.
Frequently Asked Questions
Can a fit horse tie-up?
Yes. Fitness reduces some risks but does not remove an underlying muscle disorder or every trigger.
Should horses with recurrent problems never have rest days?
Some benefit from consistent daily activity, but that does not mean exercising through an acute injury. Follow the diagnosis-specific programme.
Will dark urine always occur?
No. Its absence does not exclude muscle injury, and dark urine also has other causes.
Can affected horses return to useful work?
Many can, with appropriate diagnosis and management. The likely outcome depends on the disorder, injury severity and response to the plan.
A clear record of episodes and a carefully managed return to work are more useful than guessing at supplements. Early assessment gives your horse the best opportunity for a comfortable recovery.
For help understanding your horse’s care and preparing questions for your veterinarian, visit ASK A VET™. Urgent signs need an equine veterinarian in person.
