HEAT RELATED MYOPATHY

Any horse that is made to exercise in hot,humid weather is prone to heat related myopathy.

Signs

• Muscle weaknesss
• Muscle spasms
• Short,stilted gait
• Fatigue--inablity to continue exercising

This problem is more common in endurance horses on hot,humid days,especially horses that are not conditioned for the distance and climate.
In most cases the signs are seen towards the end of the ride,and probably relate to a combination of factors,
high body temperatures,
dehydration
electrolyte and mineral losses in sweat,in particular,sodium,potassium,chloride and magnesium.
depletion of muscle energy stores

Signs of heat related myopathy

Muscle weakness,spasms,stiff gait,high heart rate,high respiratory rate, temperature and dehydration.
Although the horse may have sweated heavily during exercise ,it may sweat very little once its sweat glands are exhausted.

Thumps

It is fairly common for horses with heat related myopathy to have thumps or synchronous diaphragmatic flutter.
Thumps does not cause a gait abnormality.
However it is a warning flag that the horse has developed srrious electrolyte,mineral,and fluid imbalances.

Treatment

• Resting the horse
• Cooling the horse
• Replacing the lost fluid and electrolytes

Reference
Lameness
Equine Research by Christine King and Richard Mansmann