Tying up

What is Tying Up?

Equine Rhabdomyolysis (ERS) or ‘tying up’ is a condition that causes the muscles running over the hind quarters to tighten and cramp up. It may also be referred to as set-fast, Azoturia or Monday morning disease. Muscular stiffness is the most common clinical sign and can range from very being mild such as a reluctance to lengthen stride, to the horse/ pony being unable to move.

Horses and ponies prone to tying up can be broadly categorised into one of two types; those where susceptibility is linked to an underlying muscle condition such as Recurrent Exertional Rhabdomolysis (RER) or Polysaccharide Storage Myopathy (PSSM), and those who do not have an underlying muscle condition.





  • Who is at risk?

    Tying up can affect any horse or pony at any time, regardless of whether or not they have an underlying muscle condition although there is usually an identifiable trigger(s).

    • Cases not linked to an underlying muscle condition are thought to be the most common form of tying-up and includes those in which susceptibility is mainly due to dietary and/ or management practices. Triggers include under-exercising and over-feeding, electrolyte imbalances and low forage, high cereal/starch diets.
    • RER involves a defect in muscle fibre contraction and commonly affects Thoroughbreds, Standardbreds and Arabs; particularly young nervous fillies in training. Triggers include stress/ excitement, prolonged box rest, high cereal/ starch diets and irregular exercise. Sufferers tend to have nervous temperaments and may be poor-doers.
    • PSSM involves a defect in carbohydrate utilisation and/or storage in the muscle and commonly affects Quarter Horses and their crosses (Paints & Appaloosas), Draughts, Warmbloods and Morgans, although cases in Anglo-Arabs, Andalusians and Cobs have also been reported in the UK. Triggers include high starch/ cereal diets, changes in exercise routine and exercising after a period of rest. Sufferers tend to be good-doers and have calm temperaments
  • RER & Cases not linked to an underlying muscle condition
    • Maximise forage intake feeding ad lib where ever possible. Do not restrict forage intake to less than 15g per kilogram of bodyweight per day dry matter. In practise this equates to approximately 18g of hay or 20-24g of haylage per kilogram of bodyweight per day in horses and ponies without access to grazing - speak to a nutritionist for more advice.
    • Soaking hay to reduce WSC (sugar plus fructan) may be helpful. Alternatively consider having your forage analysed, ideally choosing a low WSC hay over a low WSC haylage.
    • Provide a balanced supply of vitamins, minerals and quality protein by feeding the recommended ration of an appropriate compound feed or balancer
    • Additional vitamin E and selenium may help to support muscle health and reduce the risk of tying up. Daily intakes of 1500-2500iu of vitamin E and 2-2.5mg of selenium have been suggested.
    • Oil can be added at up to 100mls per 100kg of bodyweight per day to provide additional energy (calories). However simply adding oil on top of your horse’s current feed may unbalance the diet, so consider choosing a feed that already contains a higher level of oil
    • Add any additional oil gradually (approximately 100mls per week) and ensure the diet provides an additional 100iu of vitamin E for every 100mls of oil added. It may take up to 12 weeks for horses to adapt to utilising a high oil diet, so allow suitable time before assessing improvements in condition and/ or performance
    • The amount of starch that can be tolerated varies between individuals, but start by choosing a feed containing less than 15% starch
    • Do not increase feed in anticipation of increased work
    • On rest days reduce cereal based feeds by half from the evening before to the evening after
    • Maintain electrolyte balance
  • Electrolytes

    Maintain electrolyte balance in the diet. In many cases either free access to a salt lick for horses in light work or the addition of table salt for those sweating regularly is sufficient - speak to a nutritionist for more advice. Electrolyte imbalances within the individual horse rather than the diet may also be a concern in which case your vet may recommend a Fractional Electrolyte Excretion test.

  • Management Tips
    • Provide as much turnout as possible but manage access to grazing in a similar way to a laminitic to avoid large intakes of WSC (see laminitis insight for more advice)
    • Maintain a regular exercise programme avoiding box rest wherever possible
    • Take care to warm up and cool down properly before and after exercise
    • Aim to reduce stress wherever possible including during exercise, turnout and transport
  • The PSSM case

    These cases need strict dietary and exercise control. Try to get a confirmed veterinary diagnosis which is likely to include blood tests and may be a muscle biopsy.

  • Diet & Nutrition
    • Maintain a fibre based diet which contains minimal levels of NSC
    • Reduce bodyweight where necessary, aiming to maintain a body condition score (BCS) of 5 on a 1-9 scale. 
    • Do not restrict forage intake to less than 15g per kilogram of bodyweight per day dry matter. In practise this equates to approximately 18g of hay per kilogram of bodyweight per day in horses and ponies without access to grazing - speak to a nutritionist for more advice.
    • Try to ensure all hay, haylage and forage replacers contain less than 10% WSC. Although soaking hay helps to reduce WSC results are variable and cannot guarantee suitability
    • Start by feeding a balancer to ensure that vitamin, mineral and quality protein requirements are met without feeding excess energy (calories), starch and sugar
    • If additional energy (calories) is required choose feeds with a combined starch & sugar content of less than 10%
    • Try to choose feeds that have been seen to produce a low glycaemic response in some horses
    • Some additional oil may be beneficial for any PSSM case although the amount fed must be adjusted according the individual's BCS.
    • Maintain electrolyte balance and intakes of vitamin E & selenium as above
  • Management Tips
    • Maintain a regular exercise programme avoiding days off and box rest wherever possible.
    • Provide as much turnout as possible although access to grazing must be managed in the same way as for a laminitic. Consider turn out in a ménage, particularly for overweight horses
  • Post Tying Up Management

    If you suspect your horse is tying up call the vet. Remove all cereal based feeds and ensure that forage is fed at a minimum of 1.5% bodyweight dry matter per day. A balancer is ideal for good doers although high fibre, low NSC feeds can be continued for those who have difficulty maintaining weight at rest or in light work. It is essential that the reintroduction to work is made gradually under veterinary advice