Elizabeth Greene, Ph.D.
Equine Extension Specialist University of Vermont
Member, AAHS Board of Directors
[reprinted from Volume 3, No. 3 Fall 1998 Caution: Horses]
Most of us can remember a time when we have played the role of weekend warrior and paid dearly for our sudden bout of athleticism during the next few days. Many will acknowledge that they have treated their horses in a similar way as well. How do you know if your horse is just tired and stiff after that longer than expected trail ride or has tied up? The following information will help you understand the signs, degrees of severity, treatment, and management of tying up disease or rhabdomyolosis.
Rhabdomyolosis, (breakdown of striated muscles after exercise) is described by many different names depending on severity and, often, geographical location. Some of these names include: tying up, azoturia, myoglobinurea, set-fast, black water disease, and Monday morning disease. The disease often can be identified in draft horse breeds that perform hard work during the week, and are rested on the weekends without a decrease in their grain ration. Back on the job on Monday morning, the horses begin 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. Causes and Severity
A mild case of rhabdomyolosis (tying up) may result in soreness in the gluteal muscles, a painful and stiff gait, or simply a decrease in performance. The causes may include limited exercise, an anticipatory situation, or simply putting the horse in a stressful environment such as trailer loading, new locations, or loading into a starting gate or chute. In addition, young horses with viral infections (equine herpes virus 1 and influenza) have experienced bouts of tying up that were not associated with exercise.
Horses with severe rhabdomyolosis (azoturia, acute exertional rhabdomyolosis, black water disease) will show severe pain, reluctance to move, urination stance, increased heart rate and sweating. These horses will pass dark red or brown colored urine, lay down quietly or thrash in pain. Some horses may have chronic intermittent bouts of tying up, and this may be due to electrolyte deficiencies or imbalances. Dehydration can contribute to worsening bouts and result in greater kidney damage as myoglobin excretion occurs. High intensity-induced bouts (a racing or cutting competition) may be related to increased acidosis in the muscles, while glycogen depletion, dehydration, and electrolyte imbalance may contribute to endurance exercise-induced bouts (50 mile endurance ride). Testing
Your veterinarian can use a blood sample to test serum for levels of myoglobin (almost immediately), creatine kinase (approximately 4-6 hours), and aspartate aminotransferase (approximately 18-24 hours) after a suspected bout. If you suspect that your horse may be experiencing minor bouts of tying up, it will be necessary to establish normal values. Your vet may want to draw blood samples up to 30 minutes prior and 4-6 hours after exercise to evaluate creatine kinase levels in the serum. Be cautioned that diet and management can affect the values. Treatment
A mild case of tying up may be treated with a nonsteroidal anti-inflammatory (i.e. Phenylbutazone) and rest for 3-5 days with a gradual increase in exercise. A decrease in training intensity and grain intake will usually be recommended. Sedatives such as Acepromazine 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. In some chronic cases, Acepromazine may be used in a preventative effort prior to exercise, to help promote vasodilatation or opening of the outlying blood vessels. Veterinarians may give the horses immediate intravenous Thiamin or intramuscular Vitamin E and Selenium injections to aid return to health or monthly prophylactic injections to decrease potential onset of tying up episodes.
Horses exhibiting severe symptoms of rhabdomyolosis may be treated with intravenous fluids to decrease potential kidney damage due to the myoglobin excretion and shock. Nonsteroidal anti-inflammatory drugs and/or painkillers 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 rhabdomyolosis 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 rhabdomyolosis. Management strategies that reduce stressful situations and provide a consistent and calm environment may help as well. 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. Conclusions
Proper monitoring of conditioning, diet and management may significantly decrease or prevent the onset of mild to severe episodes of rhabdomyolosis. While excitability and genetics may predispose some horses to this disease, consistency in the environment, exercise protocol, and nutrition can work toward prevention or management. Horses that are affected with chronic rhabdomyolosis may require medication for continued use of the horse in a productive manner. Finally, do not burden your unfit horse with spontaneous exercise bouts (intense or endurance), as it can have a much longer and serious effect than you had planned on.
Kellon, E. M. Equine Drugs and Vaccines: A Guide for Owners and Trainers. Breakthrough Publications: Ossining, New York. 1994.
Hodgson, D. R., and R. J. Rose. The Athletic Horse: Principles and Practice of Equine Sports Medicine. W.B. Saunders Company. Philadelphia, PA. 1994.
James, R. B. How to be your own Veterinarian (sometimes): a Do-It-Yourself Guide for the Horseman. Alpine Press. Mills, WY. 1990.
Rose, R. J., and D. R. Hodgson. Manual of Equine Practice. W. B. Saunders Company. Philadelphia, PA. 1993.
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