ERS: Untying the Knot
Tying up, set fast, Monday Morning Disease, Azoturia, exertional Myoglobinuria, Myositis, or the more accurate term Equine Rhabdomyolysis Syndrome (ERS) is a myopathy where the basic mechanism for the condition remains unknown. The triggering factors and predisposing factors vary from one individual to another; therefore, the pathophysiological processes involved are likely to differ between groups of individuals and the optimal treatment/preventative regimes for one may not be ideal for another. As a result, a great deal of controversy and confusion has developed regarding the cause and approach to treatment of this condition.
Exercise is a very common triggering factor but the type and nature of the exercise which precedes an episode varies between individuals and for an individual. Not every horse is equally at risk. Certain horses tie up more easily than others: fillies and mares seeming more prone to this problem than males. Nervous, high strung or stressed horses are also more likely to tie up than are the more easygoing types.
It has been implied or assumed that all horses which show evidence of muscle pain and cramping following exercise have the same disease. ERS likely represents a pathological description of a number of muscle diseases which have common clinical signs. Two general syndromes are apparent from a clinical standpoint: 1) Sporadic Exertional Rhabdomyolysis (SER) following exercise in horses that have a previous history of satisfactory performance. 2) Recurrent exertional Rhabdomyolysis (RER) (Valberg, 1997). Whatever you call it, it means one thing: The horse's muscles are hard as rocks and in a world of hurt.
The most common cause of sporadic Exertional Rhabdomyolysis is exercise that exceeds the horse's underlying state of training. This includes both exercise at speed as well as endurance training. The incidence of muscle stiffness and SER has been observed to increase during an outbreak of respiratory disease, systemic infection and/or viral replication in muscle tissue (Valberg, 1997).
The classic case of SER occurs in a horse that has gone back to exercising after a day or two of rest. The name "Monday Morning Disease" originally came from draft horses that would "Tie-up" on their first day back to work after taking the Sabbath off. The horse has usually been fed normally on the off days and confined to an area not allowing for sufficient exercise.
RER is a common occurrence in Arabian, Standardbred, and Thoroughbred horses but is often seen in many other breeds. Stressors and a period of stall rest preceding exercise appear to trigger RER in susceptible horses. In some cases, especially in young horse, a psychogenic factor is involved (i.e. placing the horse in the starting barrier, transport, etc.). Predominantly fillies, especially those with nervous disposition, will have recurrent episodes of Rhabdomyolysis even with light exercise. About 5% of Thoroughbred race horses develop RER during the racing season, often when they trained at a gallop but held back from full racing speeds.
When episodes of Rhabdomyolysis occur in susceptible horse at very intermittent rates, the term chronic intermittent Rhabdomyolysis in used to describe this syndrome.
Clinical signs: Signs of ERS can range in severity from mild stiffness following exercise to recumbency. A horse with ERS most commonly first exhibits a stiff or stilted gait, sweats profusely, and has an elevated respiratory rate. In mild cases hindleg stiffness and a shuffling hindleg gait accompanied by general poor performance may be the only feature of the disease. As the syndrome progresses the horse seems to lose the ability to reach and extend well with the rear legs, and its strides become shorter and choppier. Upon stopping, horses are reluctant to move, males frequently posture to urinate and in severe cases myoglobinuria (the passage of dark colored urine) may be apparent.
Physical examination reveals painful muscle cramps especially over the gluteal muscles, usually in both hindlegs. The muscles in this area and also in the loin may feel hard as knots, and be warm and painful to the touch. Some horses may be in extreme pain which could be confused with Colic. In these more severe cases, myoglobinuria, increased body temperature, profuse sweating, elevated heart rate, and reluctance to move are common (Rose and Hodgson, 1993). The horse will typically appear to be very stressed with a very characteristic "anxious expression" on its face. Muscle pain usually persists for several hours. Endurance horses often show other signs of exhaustion including a rapid heart rate, dehydration, hyperthermia, synchronous diaphragmatic flutter and collapse (Valberg, 1997).
Treatment: The objective of treatment is to relieve anxiety and muscle pain, correct fluid and acid/base deficits and prevent renal compromise. Most cases of ERS require Veterinary intervention, but a knowledgeable owner can start the process before the Veterinarian arrives. As soon as the first symptoms appear, stop the animal, and blanket its back and rear right where it is standing. If stopped at once, the attack will probably be light, but a little extra exercise may turn the scales. Frequently the horse handler goes a little further, to see what develops, and this often changes a mild, into a fatal case. Since dehydration can play a major role in muscle and kidney damage, providing oral fluids during an attack will be helpful.
Prevention of further episodes of ERS in susceptible horses should include standardized daily routines and providing an environment that minimizes stressors. If a horse has a day off from performance activities, the amount of feed given should be adjusted appropriately. Often times this requires the concentrate feed to be fed at 1/2 the rate from the evening before until after the feed on the morning after the rest day. If there is a longer period of rest, it is worth decreasing the amount of feed and/or changing to one with a lower protein/energy level. Feeding increased amounts or increased energy/protein content feeds, prior to an anticipated increase in exercise level of a horse, should not be done until after the increase in workload and only then if required by the individual animal.
Current data suggests that the occurrence of ERS coincides with an increased rate of oxygen free radical production within the muscle cells which exceeds the cells antioxidant defense systems ability to cope with the excesses. Strenuous exercise is characterized by increased formation of lactic acid and loss of muscle ATP and through these to an increase in the rate of oxygen free radical production within the muscle cells. If a horses natural antioxidant defense system is insufficient in anyway, the free radicals can cause damage to the muscle fibers and to a loss in cell viability. Without the proper functioning of antioxidants in the horse's body, health, production and performance are jeopardized. An animal's body is equipped with a variety of protective mechanisms to neutralize free-radicals. The "glutathione antioxidant system" is foremost among these internal protective systems because glutathione participates directly in the destruction of reactive oxygen compounds. Other lesser antioxidants like vitamins C and E and the trace mineral Selenium depend on GSH for their function. As a dietary supplement Anti-ROM provides those elements essential to facilitate cellular glutathione (GSH) replenishment, to help maintain optimum GSH levels. Anti-ROM is the only horse dietary supplement of its kind that contains GlutaSynTM, a US patented natural food supplement which assists the body in maintaining optimal concentrations of GSH.
In the past, a variety of different treatments and prevention programs for ERS have included various levels of antioxidants especially Vitamin E and Selenium. The success or failure of their use directly is in relationship to the chemical form of these nutrients and the status of the GSH within the animal's body. Anti-ROM is the only dietary supplement on the market today that properly addresses both areas of concern.
Of all the treatments used to treat ERS, few have been examined critically for their efficiency. However, most equine Veterinarians and professional Nutritionists agree that nutritional modification of skeletal muscle may help in the prevention of skeletal muscle damage.
There is no guarantee of total prevention of ERS, although improved management and specific supplementation of horses at risk with Anti-ROM gives a good chance of improved athletic ability and a better chance to "Untie the knot of tying up".
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