Page 475 - The Veterinary Care of the Horse

MINIMIZING STRESS

Reducing stress of any kind will benefit susceptible horses. Feeding and exercising theses
VetBooks.ir horses first can help if anticipation of either event causes excitement or anxiety. They may

benefit from being stabled near a calm companion or in a quiet corner of the yard.

MEDICATION

• A low dose of ACP prior to exercise may help prevent ERS in excitable horses.
• Suppressing the oestrous cycles of affected mares and fillies with progesterone is

sometimes helpful.

• Drugs such as dantrolene sodium and phenytoin which influence nerve and muscle cell
function appear to help prevent the disease in some horses. However, these drugs are

expensive and cannot be given to competing horses as they would be considered an
illegal substance.

Prognosis

This is variable depending on the individual horse, its management and intended use. Some
horses have a single attack and make a full recovery. Others have repeated episodes despite

careful management. With recurrent cases, muscle wasting and scarring can eventually occur
and this limits the ability of the horse to work.

POLYSACCHARIDE STORAGE MYOPATHY (PSSM)

Polysaccharide storage myopathy (PSSM) is a metabolic disorder and there are currently two
recognized forms of the disease. Horses with type 1 PSSM (PSSM1) have a mutation of the

gene that codes for glycogen synthase 1, an enzyme that converts glucose in the bloodstream
to glycogen stored in skeletal muscle. The enzyme is overactive in affected horses leading to
abnormal accumulation of glycogen in the skeletal muscle fibres. These animals are unable to

release this stored energy for normal muscle function and they experience painful muscle
spasm while exercising. The condition is inherited and is most prevalent in draught horses,

Quarter Horses and Warmbloods but is also recognized in other breeds. With type 2
polysaccharide storage myopathy (PSSM2) there is abnormal clumping of glycogen in the

muscles, but affected horses do not have the glycogen synthase mutation and the cause is
unknown.