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RECURRENT EXERTIONAL RHABDOMYOLYSIS 

ETIOLOGY 

  • Recurrent exertional rhabdomyolysis (RER) is a genetic disease (autosomal dominant heritable trait) seen in several breeds, namely Thoroughbreds, Arabians, and Standardbreds, and tends to be more common in highstrung or nervous fillies. 
  • RER is characterized by chronic or recurrent bouts of “tying up” in fit horses, usually during submaximal training, and can also be triggered by stress or excitement. 
  • RER is distinct from sporadic exertional rhadomyolysis, which occurs when horses are exercised in excess of their fitness level and can be exacerbated or brought on by extreme environmental conditions (high heat and humidity), and/or electrolyte and energy imbalances. 
  • Clinical signs of RER or “tying up” include stiff painful muscles, lameness, sweating, shortened stride and exercise intolerance following onset of an exercise bout. 
  • Dysfunction of the sarcoplasmic reticulum surrounding skeletal muscle, which leads to abnormal calcium storage and release and subsequent prolonged muscle contraction and necrosis, is thought to be the underlying mechanism. 

MANAGEMENT RECOMMENDATIONS 

  • Daily low stress exercise is essential, whether in the form of turnout, longeing or riding. 
  • Stall rest is not recommended following an episode of tying up. Complete stall rest is counterproductive and may increase the likelihood that the horse will resume tying up episodes when put back into training. 
  • The initial muscle pain usually subsides within 24 hours of acute RER, and daily turnout in a small paddock can be provided at this time. 
  • Subsequently, a gradual return to performance is recommended once serum creatine kinase and aspartate aminotransferase levels are within the normal reference ranges. 
  • Administration of dantrolene by a veterinarian ~ 1 hour prior to exercise may help with calcium regulation. 
  • Prevention of further episodes of RER in susceptible horses should include standardized daily routines and an environment that minimizes stress. 

DIETARY RECOMMENDATIONS 

  • Added fat and fibre rations with controlled starch and sugar content, supplied primarily with good quality grass or grass/legume mix hay are most suitable for horses with RER. 
  • The diet should be fortified to include a balanced amino acid, vitamin and mineral content that complements the appropriate energy intake (energy requirements tend to be high for these horses). 
  • An added fat and digestible fibre ration while limiting dietary starches and sugar provides a safe and calm source of calories to support body condition and performance. 
  • Dietary supplementation with vitamin E (600 to 2000 IU/day) may be beneficial. 
  • Provide free choice access to salt and fresh, clean water at all times. 

SUGGESTED PURINA PRODUCTS 

FEED NOTES 

  • Control starch levels and provide high fat and digestible fiber to maintain weight and calorie intake levels. 
  • Ensure balanced vitamin/mineral levels (added vitamin E and selenium) and electrolytes. 
  • Hydration plays a key role and should be monitored, especially during periods of intense activity and/or high temperatures. 
  • The addition of Horse-Plus may help in controlling stress. 
  • Supplementation with Pur-Athlete can provide high levels of digestible fats. 
  • Always aim for an ideal body condition. 

INCIDENTS DUE TO INSUFFICIENT TRAINING OR OCCASIONAL EXERTIONAL RHABDOMYOLYSIS 

Prevention is not associated with nutrition, but an increase in antioxidants and better hydration may help. 

RECURRENT EXERTIONAL RHABDOMYOLYSIS (RER) 

Stress and excitability are often implicated in the causation and should be taken into account. NSC levels must be controlled. 

RECOMMENDATION 

SUPERFIBRA Integri-T is a good choice. BUT for exercising and sport horses, choose EQUILIBRIUM Trimax, EVOLUTION Elite or EQUILIBRIUM XCEL-HD. 

  • For high-performing horses, EQUILIBRIUM Trimax fed according to the Purina Superior recommendation is preferred because of its high fat and calorie content and low NSC levels. 

FEED RATE PROTOCOL NOTICE 

This feeding protocol described here pertains only to Cargill Limited Horse Feeds. There is not established feeding protocol that all feed companies must follow. Purina provides two feeding rates on their tag a “Minimum” and a “Purina Superior”. The “Minimum” meets the levels established by the NRC Nutrient Requirements of Horses (2007), which will prevent all classic nutritional deficiencies. The “Purina Superior” is a greater level of fortification that promotes an optimal level of performance and immunity. By no means does that imply “Minimum” is subpar, and for the non-competitive horse, that stays home year round and has no health issues there is probably no need to exceed this level. However, if you are feeding a true equine athlete, with all the immune stresses associated with that level of competition, then the “Purina Superior” level is paramount to ensure an optimal level of performance and immunity. 

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