Page 479 - The Veterinary Care of the Horse

condition.

VetBooks.ir Prevention

•
Steps should be taken to decrease the potassium levels in the diet.
• Regular exercise and turnout is beneficial.

• Stress levels should be kept to a minimum.

Prognosis

The majority of affected animals survive although the disease is occasionally fatal if an

animal experiences recurrent and severe episodes. These horses should not be used for
breeding and special care should be taken if or when such animals require a general

anaesthetic.

FIBROTIC OR OSSIFYING MYOPATHY

This is a condition where some of the muscle fibres at the distal (lower) end of the

semitendinosus muscle are replaced with fibrous tissue or occasionally by bone. Other hind
limb muscles including the biceps femoris and semimembranosus are less commonly
affected.

Clinical signs

The horse has an abnormal hind limb gait which can appear short and choppy. This is due to

the mechanical restriction rather than pain.
Due to the loss of elasticity of the muscle, the extension of the stifle joint is limited. This

causes a shortening of the cranial (forward) phase of the stride. The limb is often advanced,
then jerked back slightly before being slapped onto the ground. It is most obvious at walk.

The condition can affect one or both hind limbs. Sometimes it is possible to palpate a
firm, non-painful thickening in the semitendinosus muscle at the lower end of the hamstrings,

behind the stifle. Abnormal tension, sensitivity and ‘jumpiness’ on palpation are often present
in the affected muscle. In some horses, muscle wasting may be visible.

Causes

The usual cause is repeated tearing or straining of the semitendinosus muscle. The muscle