Guide to Exertional Rhabdomyolysis in Horses

​Exertional Rhabdomyolysis is a common condition in horses where the muscles become painful and cramp up, usually connected with physical activity. In this article we will discuss equine exertional rhabdomyolysis in more detail, describe the symptoms, discuss the causes and explain the treatment options available. 

What is Equine Exertional Rhabdomyolysis?

Painful cramping and muscle tightness after exercise is due to the fact that the muscles are effectively dissolving. The condition can be chronic and recurring (RER) or sporadic in nature depending on the individual horse and can severely impact the horse’s performance. If the horse is a racehorse, this condition can damage their career. Whilst sporadic ER is typically preventable with some changes to the horse’s lifestyle, chronic ER can affect certain breeds more and can potentially be due to an inherited condition.

What are the symptoms of Equine Exertional Rhabdomyolysis?

Whilst these symptoms do not necessarily mean the horse has ER, it is important that the horse is seen by a veterinarian to rule this out. Common symptoms for ER include:

• Pain after exercise 
• Sweating 
• Shallow or rapid breathing
• Tremors or muscle contractions
• Renal failure

Known causes of Equine Exertional Rhabdomyolysis?

​There are several known causes for equine ER. However, it is important to note that these causes can vary depending on the type of ER. There is also ongoing research to discover more about the causes of the condition.

Sporadic ER causes include:

• Overexertion and muscle strain
• Deficiency in certain vitamins such as Vitamin E or selenium 
• Herpes infections 

Chronic ER causes include:

• Inherited conditions 
• High grain diets
• Exposure to caffeine or potassium which can cause muscle sensitivity
• Abnormal calcium regulation

What is the diagnosis for Equine Exertional Rhabdomyolysis?

As mentioned earlier, if the horse is suffering from any of the symptoms discussed, it is important to have an equine veterinarian undertake an examination. If ER is suspected, they will conduct a complete physical examination followed by taking blood samples. They may also undertake a muscle biopsy to examine the muscle fibres. Together with the blood sample analysis, the activity in the horse’s muscles can be determined. 

If it is sporadic ER, genetic testing is usually not required. However, genetic testing may be an option if chronic ER is suspected.

Treatment of Equine Exertional Rhabdomyolysis in Horses

The positive news is that there are currently several different treatment options available. Again, this will vary depending on whether the horse has sporadic or chronic ER. The treatment methods include:

Pain medications
Tranquilisers such as detomidine, xylazine or acepromazine may be prescribed to help with sedation for those horses severely suffering from pain. Other medications may also be prescribed such as anti-inflammatory medications or steroids to help address pain and discomfort. 
Muscle Relaxers
Muscle relaxers such as methocarbamol or Dantrium may be given to the horse to help reduce the contraction and tightening of the muscles. It is important that the dosage is adapted to your horse by the equine veterinarian.

IV Fluids
To prevent dehydration and help rehydrate the horse, IV fluids may be used to restore electrolytes and provide the hydration that the horse’s muscles need to recover. 
Whilst ER can be an extremely painful and uncomfortable condition for horses, there are treatments available to help reduce discomfort. However, it is imperative that horses suffering from symptoms of ER are seen by an equine professional as soon as possible. It needs to be determined whether the horse is suffering from sporadic or chronic ER as this will not only help determine the cause, but it will also heavily influence the best course of treatment available.