Page 477 - The Veterinary Care of the Horse

microscope, abnormal polysaccharide inclusions can be seen in PSSM-affected horses. This

test does not differentiate between PSSM1 and PSSM2. It is used for suspected cases of
VetBooks.ir PSSM2 in breeds including the Thoroughbred, Arabs, Cobs and Welsh ponies that have
either a low or no known incidence of the genetic mutation

PSSM1 is confirmed by genetic testing using blood or hair roots. As this test is less

invasive it is often used initially (rather than a biopsy) in breeds that have a high incidence of
the mutation, e.g. the Percheron, Belgian Draught and Quarter Horse.

Blood tests for raised creatine kinase (CK) and aspartate aminotransferase (AST) may be
helpful with elevated levels 4–6 hours post exercise as a result of release of these enzymes

from damaged muscle cells. However, not all affected horses have increased muscle enzyme
activity and there may be different responses in individual breeds.

Treatment

If you suspect your horse has PSSM, call the vet. Treatment for an acute episode is likely to
include:

• Non-steroidal anti-inflammatory drugs such as flunixin meglumine or phenylbutazone to
relieve the pain and reduce inflammation

• Tranquillizers such as acepromazine or detomidine to reduce anxiety

• Intravenous fluids if the horse has severe ERS to prevent damage to kidney tubules from
myoglobin

• Turnout into a small paddock as soon as the horse is comfortable enough

Dietary and exercise changes are the key to managing this condition. The aim is to minimize

synthesis and storage of glycogen by feeding a diet that is high in fat and low in starch and
sugar. A forage-based diet supplemented with vegetable oil, minerals and vitamins is usually

recommended. In the spring and other times when the energy content of the grass is
particularly high, grazing may need to be restricted. Affected horses should be turned out
daily and given steady, regular exercise at least four times a week. The amount of exercise

should be built up gradually and sudden changes in the amount or intensity must be avoided.

Prognosis

The prognosis is reasonably good when the above changes are implemented. Many horses are
able to continue to perform adequately. A response is usually seen within 2–4 months.