CEPS/Veterinary Extension
2938 Vet. Med. Basic Sciences Bldg.
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907

By Theresa A. Fuess, Ph.D.
Information Specialist
University of Illinois
College of Veterinary Medicine

"Tying-up is an equine muscle disorder associated with exertion," says Dr. Lydia Miller, equine veterinarian affiliated with the Extension unit at the University of Illinois College of Veterinary Medicine at Urbana. "It is also known as azoturia, exertional rhabdomyolosis, recurrent myositis, paralytic myoglobinuria, and Monday morning sickness."

The classic scenario is a heavily muscled draft horse in work that is given Sunday to rest. On Monday, when put back in work, the horse shows signs of increasing muscle stiffness and pain. The syndrome also occurs in performance horses, whether used for racing, endurance, or English or Western events. Signs may occur when the horse is just warming up, is in the middle of a workout, or is being cooled down. In all cases the affected muscles (usually in the back, loin area, and hamstrings) are tense, painful, and hard. Other signs of tying-up include increases in heart rate, respiratory rate, and temperature and may include sweating. The horse may move only with short, stilted strides or may be unable to move at all.

"Depending on the severity of the attack, muscle degeneration may occur and the urine will be reddish brown due to myoglobins (muscle proteins) in it," says Dr. Miller. "Renal failure is a possible resulting complication and cause of death." A severely affected horse should not be walked because further exertion can lead to irreversible muscle damage. Several conditions such as colic, laminitis, a broken bone, pleuritis, and hyperkalemic periodic paralysis (HYPP) can cause signs similar to tying-up but are distinctly different and require different treatment. Therefore, Dr. Miller urges horse owners to call their veterinarian at the first signs of tying-up for diagnosis and treatment.

Diagnosis is based on clinical signs and is confirmed by blood tests showing elevated levels of the muscle-specific enzymes creatine phosphokinase (CPK) and aspartase aminotransferase (AST). Recovery is monitored by the decrease of these enzymes in the blood. When both fall to normal levels, treatment can be discontinued and the horse can be put back to work. If levels of these enzymes are not elevated in the blood, then problems other than tying-up must be considered.

Emergency treatment includes a pain killer and a muscle relaxant. Your veterinarian may also administer an anti-inflammatory agent. Intravenous fluids are used for dehydration and to help flush myoglobins out of the kidneys.

Multiple factors contribute to this syndrome, and different horses are sensitive to different conditions. Regular exercise, daily turn out, a consistent
low-carbohydrate/high-fat diet, and a stress-free environment may decrease the incidence and severity of tying-up. Feeding the horse balanced electrolytes, vitamins, and minerals--especially vitamin E, selenium, and calcium--is believed to be effective. Preventive measures that reduce stress, reduce potassium depletion, and improve energy metabolism have been used with varying degrees of success. Chromium seems to decrease the effects of stress in nervous horses. Dimethyl glycine (DMG) increases the efficiency of energy metabolism. Sodium bicarbonate added to the diet as a buffer is helpful in cases of potassium depletion. Dantrolene and phenytoin are compounds used in the prevention of tying-up, but these are not allowed in horses on the race track.

"A horse can be sensitive to several different things," explains Dr. Miller. "It may not be feasible or necessary to fix them all. Learn what factors trigger an attack in your horse and work to minimize those. Work with training, turn out, feed, and environmental stress. Keep a journal to look for patterns." If you would like more information on tying-up, contact your local equine veterinarian.