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Tying up (Monday morning disease) is a syndrome that damages muscle tissue in horses. There can be several causes, so there is no single cure. Management changes depend on the breed suffering with it. We will focus on thoroughbreds in this quick review.

Racehorses that tie-up sporadically will likely suffer from an excess of their training level, metabolic exhaustion, electrolyte depletion, infections, or dietary imbalances, particularly excess of carbohydrates. Some horses are more susceptible than others.

At a microscopic level, this is due to dysregulation of calcium going in and out of the muscle cells during contraction. Triggering events include stress, excitement, lameness, high grain diets, and exercise at sub-maximal speeds.

Young fillies are most commonly affected and usually are the most nervous and highly strung.

Blood sample analysis is almost always conclusive: tying up coincides with muscle damage, which determines the release in the bloodstream of muscle specific enzymes (CK and AST). Elevations in CK and AST are diagnostic. CK spikes up in 4-6 hours following muscle damage and goes back to normal in 3-4 days. AST peaks in 24-48 hours, and drops in about 2 weeks. Their relative values are helpful in understanding when has the horse tied up and when has the horse recovered (see graph at the below).

Another form of tying-up is polysaccharide storage myopathy (PSSM), which has genetic causes. It involves abnormal accumulation of sugars in the skeletal muscles, which interfere with cell activity. There are 2 types of PSSM. Only type-2 PSSM can potentially affect thoroughbreds. PPSM can be diagnosed by analysing a muscle biopsy: a little piece of muscle is then sent to the lab for genetic testing.

What should I do after the vet has left?

  • Diet management: switch to a low starch, high-fat, balanced diet. The diet should be adjusted to include vitamin and mineral supplements, high-quality hay, and lower quantities of carbohydrates (such as grain and sweet feed). Feed companies are the best to ask for advice because they offer specific feeds.

  • Painkillers: generally administered for a few days.

  • Sedatives: low dosage of acepromezine (Sedalin, ACP or similar) can be beneficial.

  • Dantrolene: the main drug used in horses that tie up more or less frequently. This limits the release of calcium from muscle cells. We have specific protocols available (give us a call to discuss) but as a rule of thumb, it’s given when stepping up in exercise to make life easier for muscles. Give it 1h and a half before exercise.

  • Vitamin E and Selenium: they have a beneficial, anti-oxidant effect. Up to 5.000 units of vitamin E can be given daily. These should be supplemented long term.

  • Electrolytes: calcium, magnesium, potassium and sodium are essential for muscle contraction. My experience is rather than feed extra doses, try to have them already supplemented in feed as that would be more accurate. If that fails, we can supply some with our own recommendations.

  • Exercise: do not give the horse days off. Warm up walking exercise for a 30-60 minutes before ridden exercise in the morning, and one hour walking exercise in the afternoon.


Tying up is similar to our cramps: It's a syndrome of muscle fatigue, pain and spasms associated with exercise. It has many different causes.

Time Window

These episodes generally occur following exercise, especially on a Monday morning. Depending on the severity, muscle stiffness can last up to days.

Most horses are back to normal within a week - 10 days.


  • Sweating

  • Reluctance to move

  • Muscle spasms

  • Stiffness

  • Fast respiratory rate

  • Kidney failure - brown urine

  • Increased muscle enzymes (CK and AST) on blood analysis

What should I do?

In the acute period, racehorses respond well to rest, painkillers, fluids, electrolytes and a gradual return to exercise. Long term, the diet should be balanced and changes to the training regime should be introduced.

What should I NOT do?

Do not force the horse to move.

What will the vet do?

  • Administer painkillers

  • Collect a blood sample to assess CK and AST values

  • Administer electrolytes intravenously if indicated (severe cases)

  • Recommend an exercise plan

  • Prescribe Dantrolene


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