Kentucky Equine Research

The Management of Tying-Up in Sport Horses: Challenges and Successes

April 27, 2010

Stephanie Valberg, D.V.M., Ph.D., a professor at the University of Minnesota, presented four clinical cases of horses with muscle disease and recommended therapies for each.

The first case presented was a three-year-old Quarter Horse gelding with typical signs of tying-up. For this gelding, exercise intolerance and toe dragging occurred at 15-20 minutes after the onset of exercise. Physical examination revealed symmetrical muscle development and normal neurological assessment. Lameness examination uncovered no unsoundness, and resting creatine kinase (CK) levels were normal. The exercise challenge involved a two-minute walk and a two-minute trot, which was repeated for 15 minutes with careful observation. CK levels following exercise were abnormally high. Polysaccharide storage myopathy (PSSM) and malignant hyperthermia (MH) were considered possible diagnoses. Diagnostic approach included genetic testing and biopsy. Genetic testing, which normally requires a 7- to 14-day turnaround time), revealed the horse had Type 1 PSSM and MH. Nutritional management was the key to managing this horse's disease. In general, avoiding high-starch feeds is one way to treat PSSM. A low-starch, high-fat, high-fiber feed (Re-Leve®) is indicated for horses with high energy needs. PSSM horses are often easy keepers, however, so rations should not exceed daily caloric requirement. Hay with a low nonstructural carbohydrate content should be selected. The outcome for this horse was positive with less stiffness, though there was occasional recurrence of disease in spring and fall.

The second case involved an eight-year-old Dutch Warmblood gelding. He performed well for six months but then became lame in a foreleg. Once the lameness was addressed, he became difficult to ride with trouble holding the canter and periodic bucking. Lameness evaluation revealed a torn hind suspensory ligament. He was rested and then put back into work following a three-month rest. Follow-up physical examination revealed weight loss and tight musculature, especially over the back. When lunged, he was explosive initially and then lost all enthusiasm. Muscle biopsy revealed excessive glycogen concentrations. The genetic test for Type 1 PSSM was normal. The diagnosis, therefore, was Type 2 PSSM. Reworking this gelding's nutrition helped significantly. Alfalfa hay was replaced with a low-NSC hay, and circulating fat was increased by feeding a moderate amount of Re-Leve®. Exercise included light work, with collection and canter work beginning after one month. The horse returned to normal with this protocol.

The third case was a 10-year-old Quarter Horse that was used for dressage. He was being fed a high-fat diet and grass hay. He had chronic lameness issues. After a long, hard lesson, the horse seemed to be suffering from tying-up with stiffness and mild elevation of CK. The owner felt the gelding's gaits were not as fluid as they had been, particularly the canter. He became incredibly short-strided and stiff. Genetic testing revealed no PSSM or MH. Muscle biopsy revealed huge lipid droplets in certain fibers, and the notion of a lipid storage myopathy was advanced by Valberg. To manage this horse, he was placed on oats and a ration balancer as well as an appropriate grass hay. He was turned out as often as possible, and he recovered fully.

The final case presented was a four-year-old Thoroughbred-Quarter Horse filly that had recently switched careers to be an event horse. She had mild lameness, and hock arthritis was found. After a 15-minute exercise test, her CK was elevated. The history and clinical signs, as well as muscle biopsy, pointed to a diagnosis of recurrent exertional rhabdomyolysis (RER). The disease is most often seen in young, nervous fillies, a description that fit this filly perfectly. The management approach included a clear-cut routine, maximal turnout, and a high-fat, low-starch feed (Re-Leve®). The filly continued to do well until she went off of her feed. Endoscopy revealed gastric ulcers, and treatment cleared up that problem. The mare continued on her feed, and she has not had another tying-up episode since she was begun on the new management regime.

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