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Equine Health Resource

Tying-Up, Recurrent Exertional Rhabdomyolysis

Synonyms: Azoturia, Cording Up, Exertional Myopathy, Holiday or Monday Morning Disease, Myositis Paralytic Myoglobinuria, Over-Straining Sickeness, Black Water Disease

As researchers have learned more about muscle disorders, it has become clear that the term “tying-up” consists of several muscle disorders. Recurrent Exertional Rhabdomyolysis (RER) is one of these.

RER is a painful muscular disorder brought on by exercise. It is more common in Thoroughbreds and some other light breeds. In this condition, muscles groups along the back, pelvis and rump become hard and sore during exercise. Muscle cells are damaged, and their inner contents leaked into the circulation. Muscle pigments (myoglobin) are released from this damaged muscle into the blood and filtered through the kidneys, often resulting in brownish coffee-colored urine, and possibly causing kidney damage.

Horses with RER can show a wide variety of signs. The key is that the signs are shown during or immediately after exercise. Along with stopping under saddle, seeming back pain, spasm, and swelling, other classic signs are reluctance to move and an appearance of stiffness and soreness. Severely affected horses can also show signs similar to colic: pawing, sweating, stretching and other signs.

Prompt treatment is required to prevent life-threatening kidney damage. It is important to determine the nature of any tying up episode early in the process, so the proper preventative steps and management programs can be instituted right away.

RER is caused by defective calcium metabolism in the muscle cell. The precise genetic origin is still not fully known. RER can also occur as a consequence of nutritional deficiencies and certain metabolic diseases. Regardless of the cause, a horse that develops RER must have a history of having been recently exercised.

While the signs of Tying Up may seem obvious, confirmation of the diagnosis of the condition requires blood testing to look for elevated muscle enzymes. For horses that have repeated problems with ER, muscle biopsy and microscopic examination (by a pathologist with a special interest in these disorders) is required to understand the problem and institute the proper treatment and management and to know the prognosis.


  • What changes should I make in management to prevent this condition in the future?
  • If it happens again, what can I do to begin treatment until you arrive?
  • What is the underlying disorder behind these episodes of tying up?

    Exercise and condition horses gradually, with a set routine that increases over a reasonable period of time.

    Feed only as much high sugar grain as necessary to perform the work. Instead of grain, consider the use of one of the commercial high fat, low carbohydrate feeds that are designed for performance horses. I recommend feeding as much fat as the horse will eat, around 1 lb per 1000 lb horse per day.

    Test horses for genetic disorders that may cause this syndrome.

    Do not ask a horse that has rested for a long time to exercise intensely. If your horse is "high-strung" minimize stresses in their environment and use extra caution in developing their exercise routine.

    If a horse has a bout of tying-up, let them rest in place until your vet arrives. Provide the horse with free access to water.

    If you are on the trail when a horse ties up: I would give a single dose of flunixin (Banamine) or bute if you have it, offer water if that is possible, loosen girth or remove saddle, let the horse rest 30-60 minutes or until the medication begins working and he is willing to move forward slowly, and then try to lead him to the closest reasonable destination (camp or trailer). I would try to avoid pushing the horse hard against his will, as this tends to worsen the signs. If the horse can walk, lead them at a slow, steady walk until reaching the destination. Rest frequently for a few minutes at a time if the horse seems to slow, and then continue.

    Author: Doug Thal DVM Dipl. ABVP


    Valberg, S. Muscling In on the Causes of Tying Up, in Proceedings AAEP 58th Ann Conv, Frank J. Milne State-of-the-Art Lecture 2012, 85-123.


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