August 24, 2020


ysis, and equine-rhabdomyolysis syndrome. A great deal of controversy has arisen regarding the cause of this syndrome; however, it has become clear. In equine practice, despite the fact that cases of acute sporadic rhabdomyolysis ( ie, ‘tying up’) are quite common, the pathophysiology of this disease is still. Learn about the veterinary topic of Exertional Myopathies in Horses. Although exertional rhabdomyolysis was previously considered a single disease.

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Equine Neuromuscular Diagnostic Laboratory. ER continues to be a performance-limiting or career-ending disorder for many equine athletes. The term ER literally means the dissolution of muscle cells with exercise. By determining the underlying form of ER that a horse is suffering from, specific management strategies can be employed to control symptoms. Clinical signs of ER usually occur shortly after the beginning of exercise.

The most common sign is firm and painful muscles over the lumbar loin and sacral croup regions of the topline, including the large gluteal muscles.

Excessive sweating, quick, shallow breathing, rapid heart rate, and muscle tremors are also noticed. In extreme cases, horses may be reluctant or refuse to move and may produce discolored urine due to the release of myoglobin from damaged muscle tissue. Episodes of ER vary from subclinical to severe in which massive muscle necrosis and renal failure from myoglobinuria occurs. If a horse shows signs of ER a veterinarian will determine how severe the problem is, relieve the muscle pain and cramping, provide oral or intravenous fluids to correct dehydration and flush myoglobin from the kidneys and put a management plan in place.

Exertional Rhabdomyolysis (ER)

Proteins measured in a blood sample can determine the extent of the muscle damage. This is a separate test from genetic testing for PSSM1 and is used to see if muscle damage has occurred.

Two muscle proteins often used as a measure of muscle damage include creatine kinase CK equjne aspartate transaminase AST. When muscle cells are damaged, they release these proteins into the bloodstream within hours. A blood sample taken to measure these proteins can determine how much muscle damage has occurred. With many forms of tying-up, blood CK activity returns to normal within days if horses are rested.

It is very common for horses with PSSM1 to have equinf CK activities even if they equlne rested for weeks after an episode of tying-up. To determine the specific cause of ER a complete veterinary evaluation is needed.

Diagnostic work up of myopathies. One way to see if tying-up occurs is to rhabxomyolysis an exercise test. This is useful if a horse shows no signs of muscle stiffness when a veterinarian performs a physical rhabxomyolysis but still suspects the horse suffers from a form of tying-up.

The horse should be worked in a round pen at a walk and trot for 15 minutes. If the horse shows any signs of persistent muscle stiffness, the test should rhwbdomyolysis. The idea here is not to produce signs of stiffness, but to see if this mild form of exercise cases slight muscle damage. In cooperation with your veterinarian, have a blood sample drawn hours after the exercise test.


The blood sample is not informative if taken right after exercise, as the CK protein has not had enough time to leak out of the muscle cells. For more details on the exercise challenge test, see the recommended diagnostic work-up. Muscle has a remarkable ability to repair itself.

After an episode of tying-up, the muscle cells usually heal completely within three to four weeks without any scarring. If the damage is severe, you may notice that the horse’s muscle mass decreases in size as the body removes the damaged proteins. The muscle mass usually returns within two to four months.

ER rhaabdomyolysis can be subdivided into sporadic and chronic forms. Horses that experience a single episode or infrequent episodes of ER are categorized as having sporadic ER, whereas horses that have repeated episodes of ER accompanied by increased muscle enzyme activity, even with mild exertion, are classified as having chronic ER.

Rather something extrinsic in the environment has caused muscle cells to be damaged.

Sporadic ER occurs most commonly in horses that are exercised in excess of their level of conditioning. This happens frequently when a training program is accelerated too abruptly, particularly after rhabfomyolysis idle period of a few days, weeks or months. Endurance competitions held on hot, humid days may elicit sporadic ER in susceptible horses because of high body temperatures, loss of fluid and electrolytes in sweat, and depletion of muscle energy stores.

These metabolic imbalances can lead to muscle dysfunction and damage. In some instances, horses seem more prone rhabodmyolysis ER following respiratory infections. Therefore, horses should not be exercised if they have a fever, cough, nasal discharge, or other signs of respiratory compromise. With the first episodes of ER horses should be rested for the first h in a stall until they can move about comfortably without pronounced stiffness.

Small paddock turn out where the horse is quiet can be provided. Hand walking should be done with caution as even 10 min of forced walking can trigger another episode of ER at this stage. Re-examination by a veterinarian one to two weeks after the episode of ER will determine when to put the horse back rhabdimyolysis a gradual exercise program.

Nutritional Management of Sporadic ER A well-designed exercise program and a nutritionally balanced diet with appropriate caloric intake and adequate vitamins and minerals are the core elements of preventing future episodes of ER.

Vitamin E and selenium Adequate amounts of vitamin E and selenium prevent the detrimental interaction of peroxides with lipid membranes of the muscle cell. Many feeds, particularly those designed for horses with ER provide adequate selenium supplementation and caution should be taken not to provide excessive selenium in the diet. Vitamin E is provided in most diets by green grasses, well-cured hay, and rice bran.


The best approach is to measure whole blood selenium and serum vitamin E to determine if a horse is deficient and then to design supplementation based on those levels. More information about selecting the correct Vitamin E supplement can be found here. Electrolytes and minerals Horses performing in hot weather often develop electrolyte imbalances, particularly if exercise continues for several hours.

Free-choice access to loose salt or a salt block should be provided to these horses, or alternatively, one to four ounces of salt can be added to the feed daily.

Extreme climatic conditions may necessitate the use of commercial electrolyte mixtures containing a 2: Fresh water should be available to horses at all times, especially if they are being supplemented with electrolytes. Dietary imbalances of electrolytes, particularly deficiencies of sodium, potassium, and calcium, have been implicated in ER Harris Correction of imbalances may be crucial in the management of some ER cases.

Exercise programs Similar to humans horses need to be conditioned in order to comfortably perform a given level of exercise. Exercise regimes should gradually be increased after an episode of ER and a program designed to incrementally increase the duration and intensity of exercise to ensure adequate fitness and prevent further ER.

There can be several causes for chronic ER in horses. Support the College of Veterinary Medicine.

Exertional Rhabdomyolysis (ER) | College of Veterinary Medicine at MSU

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