Broadly speaking, muscle diseases (myopathies) are either present from birth (genetic disorders) or develop spontaneously during adulthood (acquired disorders). Those present from birth may not be obvious until adulthood.
The medical term for the most common muscular disorder is recurrent exertional rhabdomyolysis (RER), resulting in a syndrome of muscle cramping that occurs during exercise. RER is also known as tying up, setfast, Monday morning disease and azoturia. Horses that experience RER either have an underlying myopathy or have been physically overexerted.
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