There are many names for “it”: azoturia, set fast, paralytic myoglobinuria, and chronic exertional rhabdomyolysis (ER), but most of us know “it” as tying up. It is a common muscle problem in horses with multiple causes. The most common syndromes include Polysaccharide Storage Myopathy (PSSM), Recurrent Exercise Rhabdomyolysis (RER), vitamin/mineral deficiency, electrolyte imbalance, exhaustive exercise, especially on hot, humid days. Some horses can have chronic episodes starting at a young age when exercised lightly. Depending on the cause of tying up, keeping your horse well hydrated and fit for exercise can help reduce tying up episodes.
PSSM is a common cause of chronic tying up in Quarter Horses, Paints, Appaloosas, Warmbloods, and Draft Breeds, although other breeds may be affected. In PSSM, horses have a genetic defect in the muscle cells which results in excessive storage of sugar known as glycogen. Most horse owners have reported that horses with PSSM have exercise intolerance. A genetic test is available for some breeds of horses that require only a hair sample or blood test. However, other breeds may need to have a muscle biopsy performed to diagnose the disorder. The diet for these horses should consist of low starch/low sugar feeds with a high fat percent.. Any change in diet should be done gradually. These horses should also have daily exercise to prevent muscle stiffness and liberal access to turnout.
Recurrent Exercise Rhabdomyolysis (RER) is another cause for chronic tying up and occurs when there is an abnormality in the way muscle cells regulate intracellular calcium. This type of tying up is not due to the calcium in the horse’s diet, but is also believed to be a genetic defect in the muscle cell. RER episodes occur with exercise or excitement, so keeping the horse calm is one part of prevention. Getting the horse conditioned to the stimuli, providing controlled daily exercise, and the least amount of time in the stall possible are the best ways to prevent RER. A proper diet for these horses can be difficult because most are in training; they need enough calories to maintain that level without making them high strung. Fat is a good energy source without making them “hot”. The most common breeds with RER are Arabians, Standardbreds, and Thoroughbreds.
Tying up episodes can range from mild to severe. A horse can present with a tucked-up abdomen, excessive sweating, muscle stiffness, reluctance to move, muscle twitching in the flank, a camped-out position, back muscle pain and/or a shortened stride. Sometimes this can happen very quickly or, in the cases with RER, some Standardbreds have been known to tie up 15 minutes after exercise. If your horse presents with these symptoms, call your veterinarian and do not move the horse but keep them standing. Offer the horse water and prevent them from getting chilled with a blanket. In cases of significant muscle damage, myoglobin (the protein which carries oxygen in the muscle cell) may be released, resulting in red or dark colored urine. Fluids, under the direction of your veterinarian, may be required to prevent kidney damage.
A horse who chronically ties up should be examined by a veterinarian to rule out specific diseases that could be the cause. There is still much to learn about the causes of tying up, but research continues to offer new strategies to manage this difficult condition.