Equine Rhabdomyolysis Syndrome

Equine rhabdomyolysis syndrome (ERS), commonly called tying up, represents a milder form of the condition known as exertional sympathy. Mares seem to be more prone to the condition and some horses develop recurrent attacks. It attacks horses while they are working and is often more prevalent when they are also subjected to environmental stress. There are two forms of equine rhabdomyolysis syndrome: sporadic and chronic.

  1. Cause

    • This condition occurs in heavily exercised horses who continue to consume a high-carbohydrate diet even when the exercise is temporarily discontinued. This consumption causes an accumulation in the muscles of a carbohydrate storage compound called glycogen.

    Effects on the Body

    • When training is resumed, the horse suffers a great deal of pain and has trouble moving due to the release of the excess glycogen, which rapidly breaks down to produce blood sugar. This in turn produces lactic acid, which builds up to levels well beyond what can be removed during metabolism. Lactic acid damages skeletal muscle and causes the release of muscle enzymes and myoglobin. When myoglobin is released in the urine, it blocks the nephrons-- basic working unit of the kidney, causing acute kidney failure.

    Sporadic

    • Sporadic ER is usually seen in horses that have always worked well but suddenly show signs of tying up. It occurs commonly when the level of training suddenly increases, forcing the muscles to work harder than they are used to. It can also occur during exhaustive exercise such as an endurance race. High body temperature, loss of electrolytes and depletion of energy stores all have a role to play in an attack of this nature.

    Chronic

    • Generally seen in younger horses, chronic ER is typified by recurrent attacks that occur whenever the horse is exercised. Recurrent exertional rhabdomyolysis is one type of chronic ER. It occurs in many breeds of horses and seems to be due to an abnormality in the way muscle cells regulate calcium during contraction. Excitement and stress also seem to play a part in the development of the condition in that it often occurs in fillies at their first race or during a horse's first show.

    Symptoms

    • Symptoms of equine rhabdomyolysis syndrome include stiffness, muscle tremors, anxiety and sometimes sweating. The muscle of the loin and hindquarters, in particular, are tense, hard and painful.

    Prevention

    • Withholding grain during periods of inactivity, maintaining a regular exercise program with at least some activity every day and starting all exercise activities slowly and increasing them gradually will help to prevent ERS. Fat and fiber meals can reduce episodes of tying-up in horses with recurrent exertional rhabdomyolysis (RER). Vitamin E and selenium may also prevent recurrent attacks in some horses.

    Treatment

    • All physical training should be stopped if the horse owner suspects that the horse is developing equine rhabdomyolysis syndrome. The slightest amount of activity--even returning to the stall--can cause the syndrome to progress. Notify the veterinarian immediately. Blanket the horse to keep him warm until the vet arrives. NSAIDS (non-steroidal anti-inflammatory medications) are given to the horse to relieve stiffness for numerous days after the onset of symptoms. Tranquilizers such as acepromazine and hesperidins may aid in the removal of lactic acid by improving circulation to the muscles.