alt=Equine Musculoskeletal Engraving|thumb|Equine Musculoskeletal Engraving

Equine exertional rhabdomyolysis (ER) is a syndrome that affects the skeletal muscles within a horse. This syndrome causes the muscle to break down which is generally associated with exercise and diet regime. Depending on the severity, there are various types of ER, including sporadic (i.e., Tying-Up, Monday Morning Sickness/Disease, Azoturia) and chronic (i.e., Polysaccharide Storage Myopathy (PSSM) and Recurrent Exertional Rhabdomyolysis (RER)).

Types of equine exertional rhabdomyolysis (ER)

Equine Exertional Rhabdomyolysis (ER) is a general term used to define both sporadic - (infrequent) and chronic - (repeated) manifestations of the condition. The severity of the condition defines what type of ER a horse has.

  • Excessive heat with electrolyte imbalances, especially seen with potassium
  • The work of a horse after a period of rest, if diet was not reduced.
  • Hormone imbalance
  • Thyroid hormone imbalance with hypothyroidism
  • Vitamin E deficiency
  • Muscles worked without proper training causes contractions leading to myopathy

Chronic ER can include the following factors:

  • Genetic excessive storage of glycogen (carbohydrate storage in the body) paired with abnormal polysaccharide sugar intake - strictly related to Polysaccharide Storage Myopathy (PSSM)
  • Excessive rest periods followed by intense return to work on a high-grain diet - Strictly related to Polysaccharide Storage Myopathy (PSSM)
  • Abnormal muscle contractions - strictly related to Recurrent Exertional Rhabdomyolysis (RER)
  • Hormonal imbalances - strictly related to Recurrent Exertional Rhabdomyolysis (RER)
  • Stress and over stimulation - strictly related to Recurrent Exertional Rhabdomyolysis (RER) each can cause signs of ER. The blister beetle is known to distribute a toxin known as cantharidin. This toxin if ingested can cause severe gastrointestinal issues, which if left untreated could cause nephritis. Ingesting ionophores toxins, such as those found in day blooming jasmine, can cause the heart muscle to become inflamed, which can bring about signs of ER. Other signs include excessive sweating, and labored breathing, which can be caused from the pain, increased pulse which also can be attributed to the pain, red urine which can be directly linked to potential myoglobin being released into the kidneys. To improve blood flow to the muscles and help to with muscle spasms, heat therapy and equine massage may be beneficial.

Severe cases

A horse may need fluids, especially if its urine is colored, it is receiving NSAIDs, or it is dehydrated. Fluids increase the production of urine that, in turn, helps flush out the excess, and potentially damaging, myoglobin from the kidneys and reduce NSAID-produced kidney damage. Fluids should be administered until the urine is clear, which usually takes from a few hours to a few days.