Sporadic exertional  rhabdomyolysis (azoturia, tying up in horses)

Azoturia is a metabolic condition of horses that is characterized by reluctance to move and poor performance. Polo-horses, thorough bred, Standard bred and female race horses are at greater risk to the disease.

Aetiology: The exact cause of the disease is not well established. It may be associated with hypothyroidism, sodium or potassium deficiency, viral infections, carbohydrate rice diet, and abnormal metabolic functions. Most cases of azoturia are linked to long duration and high intensity exercise leading to metabolic exhaustion and hyperthermia. Prolonged period (days to weeks) of rest to performing horses is an important predisposing factor.

Clinical findings: Variable signs ranging from poor performance to recumbency and death are recorded in the disease. Common signs are poor performance, stiff or short stepping gait, reluctance to move, apprehension, anorexia, and frequent shifting of weight from one leg to other. Severe cases may have hard and painful muscle, (usually the gluteal muscles), excessive sweating, and elevated heart and respiratory rates. Hyperthermia, especially after exercise, and myoglobinuria can be seen in some cases. Some horses suffer from chronic exertional rhabdomyolysis, which can be classified in two form viz polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis. PSSM is more commonly seen in quarter horse and related breeds, warm-blood and draft horses. Rest of few days prior to exercise is an important predisposing factor. The condition is characterized by tucked up abdomen, stiffness of hind limbs and disinclination to move. Recurrent exertional rhabdomyolysis is seen more commonly in thoroughbred and Arabian horses. The disease is supposed to occur due to abnormal regulation of intracellular calcium in skeletal muscles. There is intermittent disruption of muscle contraction.

Diagnosis: Sporadic exertional rhabdomyolysis is diagnosed on the basis of history, signs of muscle cramping, stiffness after exercise and moderate to marked increased  in activities of enzymes creatine kinase, aspartate aminotransferase and lactate dehydrogenase in serum. Affected horses have markedly elevated serum myoglobin level.

Treatment and prevention: Providing rest, correction of dehydration and electrolyte abnormalities, and prevention of secondary complications such as nephrosis and laminitis are used for prevention and amelioration of azoturia. Mildly affected horses may be given phenylbutazone (2.2. mg/kg) orally or intravenously every 12 hours. In severe cases, administration of balanced salt solution and 1.3% sodium bicarbonate solution is recommended along with pain killers like phenylbutazone or flunixin meglumine or ketoprofen.The disease can be prevented by alleviating triggering factors such as excitement and providing rest with regular access to a paddock. Balanced ration with adequate levels of selenium and vitamin E is also beneficial. Feeding of high fat, low soluble carbohydrate diet is recommended to prevent recurrent exertional rhabdomyolysis.