Azoturia, which is more correctly described as equine or exertional rhabdomyolysis syndrome (ERS) and is also referred to as set-fast, tying-up and Monday morning disease, is a disturbance of the horse’s normal muscle function. It can be compared to severe muscle cramp and it tends to happen during the early part of a horse’s exercise session, typically in the first 10-30 minutes, and often – but not always – following a period of rest.
When a horse has a severe azoturia attack, the muscle fibres are damaged and release muscle breakdown products into the bloodstream. Usually it is the large muscle masses of the horse, around the croup, loins and thigh area that are affected. Depending on how many muscle fibres are affected, this can be extremely painful so unsurprisingly the horse will be unwilling to move, may appear distressed and often sweats profusely, hence the name tying-up, which describes the condition clearly.