Tying-up: Complicated syndrome, simple management

By: Dr. Lydia Gray

The horse industry has recognized "tying up" as a muscle syndrome in horses for over a century. And there are as many names for this syndrome—Monday morning sickness, azoturia, cording up--as there are theories why it happens. This article provides an overview of the most current research about the causes, treatment and prevention of this disorder, according to the Neuromuscular Diagnostic Laboratory at the University of Minnesota College of Veterinary Medicine Equine Center.

"Tying up" is an umbrella term describing the pain and cramping of a horse’s muscles with exercise. Therefore veterinarians refer to the syndrome as "exertional rhabdomyolysis." There are two forms of ER: sporadic and chronic. The sporadic form is a one-time event that occurs in otherwise normal horses asked to perform beyond their current level of fitness. For example, an endurance horse conditioned for a 50 mile ride might tie up if the weather is particularly hot and humid. A combined training horse might tie up if moved up a level without additional conditioning. This form of tying up can be managed by correcting electrolyte imbalances, Vitamin E/Se deficiencies and conditioning programs.

The second form, chronic exertional rhabdomyolysis, is now separated into two categories. One category is horses that tie up due to polysaccharide storage myopathy (PSSM or EPSM), covered in a separate article. The other category is recurrent exertional rhabdomyolysis (RER), which refers to horses that tie up repeatedly, and is seen primarily in thoroughbreds, standardbreds and Arabians. In the past, researchers thought RER may be due to lactic acid build-up in muscles, but more recent studies point to abnormal regulation of intracellular calcium that makes muscle much more sensitive to contractions. In thoroughbreds, this abnormality may be inherited.

The signs of RER can range from mild to severe and include the following, all associated with exercise:

• Firm and painful muscles over the loin and croup
• Excessive sweating
• Quick, shallow breathing
• Increased heart rate
• Muscle tremors
• Reluctance or refusal to move
• Reddish-brown colored urine
• Lying down/inability to rise

Exercise should be stopped immediately and a veterinarian called if any of the above signs occur. Diagnosis is based on history, physical examination, bloodwork, muscle biopsy and possibly other tests. Treatment for a horse suffering from tying up includes keeping the horse hydrated by administering fluids and relieving the horse’s pain and anxiety. Depending on the results of the bloodwork, the horse may need to be stall rested and gradually reintroduced to exercise under close observation.

Preventing episodes of tying up in horses prone to RER consists of managing the diet, exercise and environment. The recommended diet has less starch and more fat, which can be accomplished a number of ways. First, make sure the horse receives 1.5 – 2.0% of his body weight in forage daily. Then, replace some or all of his grain/sweet feed with a commercial product specifically developed with fewer nonstructural carbohydrates. Depending on the product used, additional fat in the form of rice bran, oil, powder or extruded pellets may be necessary. In addition, electrolytes are recommended in the form of plain salt or commercial mixtures containing sodium, potassium and chloride for horses in heavy training/competition or in hot, humid climates.

For some horses, the combination of stress and exercise leads to an episode of tying up. Use the following suggestions from Dr. Stephanie Valberg to avoid "trigger factors" in nervous-type horses:

• Position the stall in a quiet area of the barn
• Time of training (first rather than last)
• Turn-out (if available a big advantage)
• Avoid training regimes like holding back at a gallop or intervals that excite the horse
• Tranquilize before exercise to prevent excitement
• Attention to and treatment of lameness
• Avoid stall rest or lay-up if possible, providing calm exercise if rested the day before
• If necessary, give medications that affect intracellular calcium regulation, such as dantrolene orally one hour before exercise.

Tying-up, or exertional rhabdomyolysis, is a complicated syndrome and managing a horse with the chronic form of it can be challenging. But simple adjustments in nutrition and lifestyle can prevent episodes of this painful muscle condition in most horses, and allow them to be kept in training and competition.

About Dr. Lydia Gray