It has been recognised by vets and horse owners for over 100 years and is known by a variety of different names such as Monday Morning Disease, Setfast and Tying-Up, and its medical name is exertional rhabdomyolysis.
There are two main types of exertional rhabdomyolysis, a sporadic form and a chronic form. The sporadic form is characterised by a one off or infrequent episodes of tying-up, and the chronic form is characterised by repeated episode of tying up sometimes with even just mild exertion.
How do you know if your horse has tied-up? Horses which suffer an episode of tying up can present with a range of different signs, usually a combination of muscle tremors, quick and shallow breathing, excessive sweating and painful muscles along the back and hind quarters.
More extreme cases can be so painful and uncomfortable that they will be reluctant or even refuse to move, and may have a brown or red tinge to their urine due to the amount of muscle which has been broken down.
To confirm tying up a vet will usually perform a blood test to measure the levels of two enzymes (CK and AST) which are released into the blood whenever muscle has been damaged.
The sporadic episode of tying-up is usually brought on by one of two main causes; overtraining or a deficiency or imbalance of electrolytes within the body of the horse.
An episode of tying-up due to overtraining usually comes about when the level of intensity of the horses training has been accelerated too quickly, especially after the horse has had some time off.
Tying-up brought on by an electrolyte deficiency/imbalance can also occur when a horse has been sweating excessively, with resultant loss of fluids and electrolytes from the body.
Horses that are particularly nervous or excitable are at an increased risk of tying-up.
Long-term management of this condition is centred on having a well designed appropriate controlled exercise programme and a nutritionally balanced diet with appropriate calories and vitamins.
Following an episode of tying-up horses should only have a few days free from exercise to recover. The reduction of starch levels in the diet and replacement with fat has shown to be beneficial in the reduction of the frequency of tying up.
Decreased levels of starch may also cause the horse to be calmer and so less prone to tying-up.
Chronic or repeated episodes of tying-up are usually consistent in horses which have an underlying inherited or genetic disorder, the most commonly condition is Polysaccharide Storage Myopathy PSSM which is most commonly seen in Quarter Horses, Warm bloods, and Draft breeds. PSSM causes episodes of tying-up through genetic alterations in energy metabolism of muscles. Affected horses tend to be in good body condition, and the signs tend to be brought on by a change in the horses exercise routine.
Management of PSSM is difficult because of the underlying genetic cause but involves appropriate controlled exercise and more importantly dietary management is the cornerstone of the long-term control of this condition.
This involves decreasing the levels of starch in the diet and replacing this with fats as an energy source. There are many proprietary diets with specially tailored fat and starch levels to suit horses with PSSM or which may be prone to tying-up.
But as a rule forage should still be fed at a rate of 1.5-2% of the horses bodyweight, starch levels should be decreased to 10% of the daily energy intake, with fats (usually in the form of oils) being added to the diet to make up 25% or less of the daily energy intake.
Vitamin E and selenium supplementation can also be beneficial but should be done cautiously and only with veterinary recommendation.
PSSM is usually diagnosed by taking a muscle biopsy from the muscles adjacent to the tail head, which is then sent off for testing at a laboratory where the samples are examined for any of the hallmarks signs of PSSM.
Recently some research into PSSM has identified the cause of one particular type of PSSM known as type 1 PSSM. This particular type of PSSM can now be more conveniently diagnosed by DNA testing hair roots or blood samples, without the need to take a muscle biopsy.
If you suspect that your horse is suffering from Exertional Rhabdomyolysis contact your vet for further advice.