As the workload increases for horses preparing to go out hunting or for racehorses beginning their training for the national hunt season, Exertional Rhabdomyolysis (ER) is a common problem in Ireland and can occur year-round.
For the past several hundred years, as horse owners we have struggled to care for this disease. Also referred to as tying up, azoturia or Monday morning disease. It is an exercise associated disease that leads to muscle damage, whilst over the years, we have become increasingly aware of how to recognise and how to manage the outcome we still have little knowledge of a possible cure.
Horses and ponies prone to tying up can be exposed to two types of ER; Recurrent Exertional Rhabdomyolysis (RER), an underlying muscle condition or Polysaccharide Storage Myopathy (PSSM), which is not an underlying muscle condition. Horses here in Ireland are commonly affected by RER, which is identified when the horse undergoes repeated episodes of RER (tying up).
So, what exactly is Equine Rhabdomyolysis and how does it affect the horse?
It is described as a defect in muscle fibre contraction, which is very prevalent in young Thoroughbred horses due to their high grain diet and increasing fitness level. However, ER can affect any horse or pony at any time. Most cases of this muscle condition are linked to management practises or dietary imbalances.
Clinical signs you may see of rhabdomyolysis include muscle spasms, muscle fatigue/pain, stiffness or hard muscles, high heart rate, sweating, abnormal recumbency or reluctancy to move, discoloured urine (red-brown) and in severe cases, death.
The diagnosis can be confirmed by physical examination palpating those muscle groups and your vet can take a blood sample or in some circumstances a muscle biopsy. The horse will usually show signs of pain/stiffness after exercise and the blood sample results will show an abnormal increase in muscle specific enzymes (Aspartate aminotransferase (AST) and Creatine kinase (CK)), which are associated with muscle tissue damage.
Causes: Development of ER is influenced by different factors; age, sex, temperament and diet of the horse, along with its exercise routine. These horse’s may be under exercised, over fed, have an electrolyte imbalance or high cereal/starch diets. Other triggers can include stress, excitement, prolonged box rest and irregular exercise. Sporadic cases of ER may be caused by overexertion or dietary imbalances, whereas chronic cases may be caused by dysregulation of intracellular calcium (RER). Genetic affects are another factor associated with RER but these genes have not yet been identified. As the Royal Veterinary College states; there is currently no cure, although many horses can continue to perform well if the disorder is managed appropriately.
Management and Preventative medicine
- Environment: Allow your horse access to turnout where possible whilst managing that access to grazing (feeding a minimum of 1.5-2% bodyweight/day) in a similar manner to a laminitic horse to avoid large consumption of water soluble carbohydrates.
- A regular consistent exercise programme should be maintained, avoiding prolonged periods where the horse is stalled. Reduce stress during exercise, transport and try to turnout your horse with compatible companions. Warm up, adequate stretching and a cooling down process should become part of the routine, furthermore, training should incorporate low stress exposure and mimic levels that are required at competition level to prevent the occurrence of ER. Dr. Valberg a world-renowned researcher of muscular diseases, mentions that severe cases of RER are advised to avoid giving their horse a day off after a day of intense exercise and enzyme levels are higher when horses are exercised after a day of rest.
- Nutritional input is important: Our horses need constant access to clean drinking water, a forage based diet. A mixture of fermentable fibres, fat and a balanced concentrate feed - to provide key vitamins, minerals and quality protein. Excess nutrients may contribute to the muscle problem.
- Electrolytes (sodium, potassium, chloride, calcium, magnesium) rapidly deplete when we exercise our horses especially in summertime during warmer conditions. For nervous horses, chromium supplementation has proven to be helpful by assisting glucose and glycogen metabolism.
Fortunately, as horse owners we can aim to help prevent and manage this issue using correct management practises and provide our horses with the correct feed.
Bluegrass provides feed suitable for this condition such as Re-Leve and Re-Solve which are lower in starch. The energy is provided through fat and fermentable fibres to increase the calorie intake. Both are fully fortified with appropriate levels of vitamins, minerals and contains a natural source of vitamin E, which is a powerful antioxidant.