It is now believed that the underlying problem in most cases is a derangement at different parts of the system inside the muscle cell that produces energy for muscle contraction. This can be a temporary problem brought on by particular circumstances; it may be an inherited tendency; or it may be an unusual defect in the metabolic process itself. The end result is the same, however, the muscle cells are starved for energy and cannot function normally. Muscle fibers contract and cannot relax, resulting in the cramping and pain seen clinically. High carbohydrate diets, irregular exercise programs, exercise in an unfit or inadequately trained horse, selenium and vitamin E deficiency, electrolyte deficiency, hormonal influences, overly strenuous bouts of exercise, high heat and humid conditions during exercise, and metabolic defects in muscle are some of the many causes or factors associated with the syndrome.

At this time, "tying up" seems to occur most often in the following scenarios:

1. sporadic episodes in horses whose diet and/or exercise programs have not been consistent,
2. episodes during or following strenuous exercise under hot and/or humid conditions or in an inadequately trained horse (endurance), and
3. recurrent episodes before or after exercise or perhaps unrelated to the exercise routine.
   

Horses in category #1 may be on diets inadequate in electrolytes such as sodium or potassium or out of imbalance for calcium and phosphorus. They may be fed more carbohydrate than is necessary for their exercise requirement. They may be stalled much of the time and exercised infrequently or irregularly. These cases are often handled by balancing the diet, providing regular exercise and pasture turnout, and are not likely to recur.

Horses in category # 2 have been exercised beyond the physiologic capability of the muscle tissue. Years ago, this syndrome was not uncommonly seen in horses used for endurance exercise. These equine athletes lose tremendous amounts of fluid and electrolytes in the sweat produced by exercise. They become dehydrated and very low in potassium, calcium, and chloride. The muscle cannot function under these conditions, and cramping results. These horses require large volumes of fluid to correct their deficits.

Even well trained and talented endurance horses may occasionally suffer problems under hot and humid conditions. This syndrome is now called exhausted horse syndrome as both the muscle and the horse are exactly that - exhausted. If recognized early, it is easily treated.

Horses in category #3 are the most difficult and challenging to treat. Initially, horses with recurrent episodes are treated similarly to category # 1. The diet and training program should be carefully regimented. Daily exercise is necessary, and turnout for free exercise is often important. Some horses have been identified recently as having specific defects in the metabolic process within muscle cells. Western horses, draft breeds, warm bloods, and others have been diagnosed with Polysaccharide Storage Myopathy (PSSM). These horses may have the classic signs of muscle cramping and pain. Others may just appear stiff or uncoordinated and may have exercise intolerance. Although the defect has not yet been specifically identified, it is known that these horses absorb glucose into cells much faster than normal horses. A side effect of this problem is a build-up of glycogen and an abnormal polysaccharide in the muscle cell that can be seen with special stains on a muscle biopsy. The presence of these carbohydrates is not the problem but is rather a sign that a problem exists. Fortunately, the addition of fat to the diet as an alternate energy source will often alleviate the clinical signs and enable the horse to exercise effectively and live a normal life.

Thoroughbreds and Standardbreds are thought to have a defect in the coupling process that occurs between proteins inside individual muscle fibers. Once coupled, changes in the cells occur that do not allow relaxation and the syndrome appears. Some of these cases have responded to management changes, symptomatic therapy, and occasionally specific medications. This version of the syndrome may be inherited as specific families of thoroughbreds have been identified with a greater incidence of cases than expected.

Treatment and Prevention:

• Minimize confinement - allow pasture turnout whenever
• Maintain a regular exercise program
• Feed a balanced diet at appropriate levels - minimize concentrates
• Add fat to the diet - gradually add up to 2 cups of vegetable oil per day or commercial rice bran supplement
• Always warm up prior to exercise for a period of time appropriate for the horse and the type of exercise
• Consider electrolyte supplementation especially in the warm months of the year

If you have any further questions or concerns regarding exertional rhabdomyolysis or "tying up" please call the office at 706-654-5740. There is always a veterinarian available to help.