Winston Churchill said, "No hour of life is wasted that is spent in the saddle." It's unlikely, though, that Churchill ever experienced a horse with polysaccharide storage myopathy (PSSM), one of the causes of tying-up disease. PSSM is an incredibly painful, inherited muscle condition most commonly found in quarter horses, draft horses, warmbloods and some other breeds.

With help from Morris Animal Foundation, Dr. Stephanie J. Valberg of the University of Minnesota has been studying the disorder for more than 20 years, and she's learned a lot about managing it.

"We discovered that horses with PSSM are very sensitive to diets that increase their blood sugar and insulin concentrations," Dr. Valberg says. "They develop notable muscle pain and cramping while on high-grain diets and have deficient energy when they exercise."

In horses with PSSM, glucose builds up in the muscles, making it unavailable when it's needed for energy. The disorder comes in two forms: type 1 is caused by a genetic mutation, which can be diagnosed through a DNA test of hair roots or blood. Type 2 is diagnosed by muscle biopsy, but a genetic basis has not yet been determined. Dr. Valberg's research has focused on diagnosing the disorder and managing it through specific diet and training regimens. Horses with PSSM respond favorably to a lower-starch diet supplemented with fat. However, Dr. Valberg notes, the added fat must be in balance with the horse's activity level and should never be excessive.

"Scientific evidence proves that it is not necessary to feed a horse 1 pound of fat a day as you may see recommended on the Internet," she says.

Consistent exercise is also a crucial component in treating horses with PSSM. Horses should be turned out daily, and the amount of time they spend in a stall should be reduced as much as possible. Gentle exercise should begin after the horse has been on the new diet for two weeks. If you suspect your horse has PSSM, contact your equine veterinarian and discuss appropriate diagnostic tests, because tying up can occur for reasons other than PSSM. If PSSM is confirmed, implement a diet that reduces starches and sugars and begin a gentle exercise program.

Although PSSM doesn't go away—and there are no FDA- approved drugs to treat the disorder—it can become more sporadic than chronic. With the right maintenance program and a dose of patience, both you and your horse will have more happy trails in your future.