Equine exertional rhabdomyolysis

Anatomical engraving of a horse. Wellcome V0016883

Equine Exertional Rhabdomyolysis (EER), also known as tying-up, azoturia, or Monday morning disease, is a syndrome affecting horses characterized by muscle stiffness, sweating, and reluctance to move. This condition is of significant concern in the equine industry due to its impact on the health and performance of horses. EER can affect any horse engaged in vigorous exercise, but is more commonly observed in racehorses, show horses, and endurance horses.

Causes and Pathophysiology

Equine Exertional Rhabdomyolysis is caused by an abnormal accumulation of lactic acid in the muscles, leading to muscle cell damage, inflammation, and pain. This accumulation can result from a combination of factors including overexertion, metabolic disorders, electrolyte imbalances, and genetic predispositions. In some breeds, such as Thoroughbreds and Standardbreds, there is a genetic predisposition to EER, suggesting a hereditary component to the syndrome.

The pathophysiology of EER involves the disruption of calcium regulation in muscle cells, leading to excessive contraction and, ultimately, muscle damage. This damage results in the release of muscle cell contents, including myoglobin, into the bloodstream, which can lead to further complications such as renal failure.

Symptoms

Symptoms of Equine Exertional Rhabdomyolysis include:

• Muscle stiffness and cramping
• Reluctance or inability to move
• Excessive sweating
• Rapid heart rate
• Dark urine (due to myoglobinuria)
• Elevated levels of muscle enzymes in the blood

Diagnosis

Diagnosis of EER is based on clinical signs, history of recent exercise, and laboratory tests. Blood tests are used to measure levels of muscle enzymes such as creatine kinase (CK) and aspartate aminotransferase (AST), which are elevated in cases of muscle damage. Urinalysis may also be performed to detect the presence of myoglobin.

Treatment

Treatment for Equine Exertional Rhabdomyolysis focuses on relieving symptoms and preventing further muscle damage. This may include:

• Rest and recovery
• Administration of non-steroidal anti-inflammatory drugs (NSAIDs) to reduce pain and inflammation
• Fluid therapy to prevent dehydration and aid in the elimination of myoglobin from the kidneys
• Dietary management, including the reduction of carbohydrates and the addition of fat and fiber to the diet

Prevention

Prevention of EER involves careful management of exercise routines, ensuring that horses are properly conditioned for their level of activity. Dietary management is also crucial, with a focus on providing a balanced diet that meets the horse's energy needs without overloading the muscles with glucose. Regular veterinary check-ups can help identify and manage any underlying health issues that may increase the risk of EER.

See Also

• Horse health
• Muscle disorders in horses
• Renal failure in horses