Tying up, azoturia, myoglobinurea, and Monday morning disease are some of the names you may hear when your horse has rhabdomyolysis. This breakdown of striated muscles after exercise is described by many different names depending on severity. The disease often can be identified in horses that perform hard work on a daily basis, and then are rested without a decrease in their grain ration. When the horse goes back to work, he begins to cramp up, show hindquarter stiffness, severe muscle pain and pass very dark urine. One of the suggested mechanisms is that excess glycogen is accumulated in the muscle while the horse is resting at full ration, and this is quickly broken down into lactic acid when he begins work. The high lactic acid concentration results in muscle damage, breakdown and release of myoglobin. The dark urine color is due to the increase in myoglobin being excreted and can cause kidney damage as it passes through the system.
A mild case of rhabdomyolysis (tying up) may result in soreness in the gluteal muscles, a painful and stiff gait, or simply a decrease in performance.
Horses with severe rhabdomyolysis will show severe pain, reluctance to move, increased temperature, stretched-out urination stance, elevated heart rate and sweating. These horses will pass dark red or brown colored urine.
Your veterinarian can use a blood sample to test serum for severity of the disease after a suspected bout.
A mild case of tying up may be treated with a nonsteroidal anti-inflammatory and stall rest for 3-5 days with a gradual increase in exercise. A decrease in training intensity and grain intake will usually be recommended. Sedatives which causes sedation and relaxation by depressing the central nervous system, may be given to decrease the anxiety and spasms after the horse ties up.
Horses exhibiting severe symptoms of rhabdomyolysis may be treated with DMSO and intravenous fluids to decrease potential kidney damage due to the myoglobin excretion and shock. Muscle relaxers and nonsteroidal anti-inflammatory drugs may be necessary during recovery time. As with mild cases, a sedative may be used to decrease the anxiety and help prevent thrashing or excess movement. In severe cases, it is critical to limit movement to decrease potential permanent muscle damage. Recovery time may be up to 6-8 weeks, and ability to return to work will vary with severity.
Horses that suffer from chronic attacks of rhabdomyolysis can often be managed successfully with strict exercise, management and diet protocols. A diet balanced for mineral and vitamin needs that provides a good quality hay, fresh water, and minimal grain may be adequate to control some cases of chronic rhabdomyolysis. Some horses may need to be maintained on sedatives prior to exercise or daily medication to decrease or prevent muscle damage during tying up episodes.
Proper monitoring of conditioning, diet and management maysignificantly decrease or prevent the onset of mild to severe episodes of rhabdomyolysis. While excitability and genetics may predispose some horses to this disease, consistency in the environment, exercise regimen, and nutrition can work toward prevention or management. Horses that are affected with chronic rhabdomyolysis may require medication for continued use of the horse in a productive manner.
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