Azoturia: Tying Up/Monday Morning Disease



Azoturia is a condition that affects the muscles of the horse and is often referred to as ‘set fast’ and ‘tying up’ as well as ‘Monday morning disease’. The technical term for the condition is equine rhabdomyolysis which simply translated means muscle (rhabdo) breakdown (lysis). The disease usually affects the large muscle groups of the back and hind limbs, but all muscle groups can be affected. During an attack the muscles become inflamed resulting in pain and stiffness, and when muscle fibres break down they release a pigment known as myoglobin into the urine. Most cases relate to exercise and are termed ‘exertional rhabdomyolysis’ (ER), some horses appear to be more susceptible and can experience repeat attacks, this condition is known as recurrent equine rhabdomyolysis (RER).



The disease is classically caused by excessive consumption of sugars and starches due to high cereal diets, or excessive exercise without adequate warming up/fitness levels. There are also horses for whom azoturia attacks are triggered by stress for example when they become excited at a show or are very anxious about travelling. Some horses are more prone than others. In very susceptible horses a minor change in exercise routine or feeding can trigger an attack.


Clinical signs

The clinical signs of azoturia depend very much on the severity of the case. Typically signs include:

  • Stiffness throughout the hindquarters and occasionally through the larger muscles of the forelegs
  • Shortened or restricted stride
  • Unwillingness to move
  • Sweating
  • Increased heart and respiratory rate
  • Pawing the ground
  • Attempting to lie down
  • Muscles firmness In extreme cases:
  • The muscles can appear bulged due to inflammation.
  • Passing dark, reddish-brown coloured urine – this is a result of the heavily damaged muscle fibres releasing myoglobin, which then passes in the urine
  • Unable to move potentially to the point of collapse

What to do?

If you suspect your horse is tying up stop exercise immediately and return him to the stable but do not force him to move if he is reluctant as this may worsen the level of muscle damage (you may need to transport your horse in a lorry/trailer if you are a long way from the stable). In cold weather cover your horse with a rug to keep them warm and encourage blood flow. Provide free access to water with added electrolytes if available, if your horse does not significantly improve call your vet and follow their advice.


Any horse showing moderate to severe signs requires immediate veterinary treatment which will initially involve the use of anti-inflammatory agents to both reduce pain levels and restrict the level of muscle damage that occurs. Vets will usually take blood samples from the affected horse to measure the levels of muscle enzymes present in the blood. Blood tests will be carried out to monitor recovery and determine when the horse is ready to return to work.


Carefully considered diet and exercise programmes are the most effective strategies to prevent azoturia. A balanced diet should include adequate mineral and vitamin intake with good quality forage. Cereal or high energy feeds should be kept to a minimum and should be added only according to the work schedule and fitness levels of the horse. If additional calories are required for weight gain/ energy levels then oil can be added to the diet or commercial high- fat feeds are available. When exercising adequate time should be given to warming up the horse and hard work should be followed by a period of cool down to stimulate oxygen distribution to the muscles. Horses returning to work after a period of rest should have a structured programme with a slow increase in intensity as their fitness develops.

Contributor: B&W Equine Vets

B&W Equine Vets provide nationally and internationally renowned cutting edge veterinary care which would be the backbone of our referral service. They provide the very highest level of equine veterinary care as well as performing innovative procedures. We strive to provide the highest level of professional and personal care for you and your horse or pony, whether that be be via our vastly experienced mobile team or at our equine hospital.


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