Equine rhabdomyolsis ‘Tying up’
Dealing with a horse that ties up can be challenging. If it occurs on a one off occasion we refer to it as ‘sporadic exertional rhabdomyolysis’. Recurrent exertional rhabdomyolysis should be suspected if a horse has had repeat episodes.
Why does sporadic exertional rhabdomyolysis happen?
It is not entirely known what happens at a cellular level but theories include excessive glycogen (carbohydrate) accumlation in muscles when horses are rested on a full ration, imparing normal metabolism. When exercise is resumed, the metabolism that takes place results in lactic acid build up and electrolyte disturbances both resulting in damage to muscles and release of enzymes into the bloodstream. Some horses may have a genetic predisposition to tying up, particularly Thoroughbreds and fillies seem to be the most susceptible.
Firm painful muscles, stiff gait/reluctance to move, ‘false’ colic, increase heart rate and respiratory rate, excessive sweating.
A blood sample is taken to evaluate muscles enzymes and confirm a horse has tied up. Creatinine kinase (CK) is released from mucle cells when they are damaged. It is at its highest level 2 to 12 hours after the muscle damage and can reach levels as high as 100,000 IU/litre, CK should begin decreasing back to normal levels 24-36 hours after injury. Aspartate transaminase (AST) is also released by damaged muscles and is at its highest 24 hours after damage and can reach many 1000’s IU/litre and can remain high in the blood for up to 3 weeks.
After a tying up episode, tests can be performed to re-evaluate a horse’s response to exercise; blood is taken just before exercise and 2 hours after. There should be not be any significant elevation in CK between the two samples.
Muscle biopsies may be taken if a horse is tying up very regularly to evaluate the degree of tissue damage and to look for evidence of the hereditary conditions.
Treatment and prevention
Rest is very important to ensure no further damage occurs to the muscles. The rest period will depend on the severity of the muscle damage. Pain relief is necessary but must not be given at too high levels – when muscles are damaged they release a substance called myoglobin which is damaging to the kidneys – drugs like bute can also be damaging to the kidneys and are more likely to be if they are given to a dehydrated horse. Access to water is important to ensure rehydration, fresh water and water containing an electrolyte should be offered. If a horse is more severely tied up, intravenous fluids may be necessary. If the horse is quite distressed mild sedation may be given.
Management is the key to prevention; a proper warm up before exercise and regular exercise with no days off. Turnout is preferable. Diet should be low in carbohydrates, protein levels should also not be excessive. Energy can be supplemented using vegetable oils, the diet should be high in fibre and vitamins, minerals & electrolytes must be optimal. Vitamin E is often supplemented to enhance muscle metabolism.