The exact nature of the defect in metabolism in these cells that makes them prone to damage with exercise isn't clear, but it appears they rely too heavily on carbohydrate and not enough on fat. Limiting carbohydrate intake and feeding increased fat appears to "train" their muscles to make better use of fat as an energy source and relieve many of the symptoms.
Definitive diagnosis can only be made by muscle biopsy, although many opt for a trial of low-carbohydrate, high-fat diet rather than a biopsy. The current basic diet recommendation for an EPSSM horse consists of hay and substitution of the grain ratio with alfalfa pellets and up to two cups of vegetable oil. One cup of oil is the calorie equivalent of about 2.5 to 3 pounds of grain. Improvements in muscle tone (more relaxed) and frequency/severity of tying-up may appear rapidly or may take time.
Any oil will do, but Uckele's Coco-Soya (www.uckele.com 800-248-0330, $12.30/gallon) can be a good choice. This blend of coconut and soy soil is cold pressed and unprocessed, retaining high levels of natural antioxidants. It's highly palatable. The coconut oil is high in medium chain length triglycerides, which are able to enter the muscle cell without requiring a carrier protein like the longer chain triglycerides found in other vegetable oils do.
Treatment of an EPSSM-related tying-up episode is the same as for any other type of tying-up. Movement can worsen muscle damage and should be avoided. Muscle relaxants, tranquilizers and intravenous calcium and magnesium may be used to help the stiff, painful muscles relax. Intravenous fluids help prevent muscle pigments from clogging the kidneys.
Muscle Tears
Another problem that frequently occurs in Quarter Horses is muscle tears, due to the combination of heavy muscling and the type of work many Quarter Horses do. These typically involve long, large muscle groups of the upper hind leg, when viewed from behind.
Soreness and stiffness present at the time of the initial injury may resolve only to be followed by the development of a shortened gait on the involved side and a characteristic slapping down of the foot, called goosestepping. This occurs when the injured area of muscle heals by formation of a thick, tight scar that lacks the ability to stretch that normal muscle has.
The condition is called fibrotic myopathy. In some cases, calcification/calcium deposits may also form, called calcific myopathy. Surgical removal of the scarred and/or calcified portion of muscle is the usual treatment. Shock-wave therapy also has been tried.
