If you have horses, you have probably heard of tying up. There are really three types of tying up. The first can be due to overexertion in horses that are not in good enough physical shape to undergo the exercise they are asked to perform. It can also be due to heat exhaustion or electrolyte imbalances. These horses have an increased respiratory rate, elevated temperature, sweating, muscle stiffness, and shifting lameness in the hind legs. After treatment the syndrome does not recur if the horse is not over exercised again unless the horse has one of the two other types of tying up. The second type, recurrent tying up in thoroughbreds and in some Standardbreds, is due to a genetic muscle defect that leads to abnormal calcium regulation.
The third type is also recurrent but is common in quarter horses, draft horses, and other breeds that is due to a defect in storing the compound glycogen in the muscle; it’s called polysaccharide storage myopathy or PSSM. This is also a genetic defect, and symptoms may be very mild with only intermittent lameness or poor performance. Because it is a genetic problem, there is a blood test or hair test that can be performed on many of the affected horses to diagnose PSSM. If the blood or hair test is negative but it is still believed to be PSSM, a muscle biopsy is required to make the diagnosis. In general, preventing this disease is effective with a diet change to a low-starch high-fat feed. So if you have a horse that ties up, just realize that it can be a complicated issue depending on the breed and circumstances, and that treatment requires an accurate diagnosis to determine the type of tying up.