The rare Grey Shire Horse, was bred solely for the purpose of pulling large weight (mostly for pulling coal out of mines). Because they were bred specifically for this, it’s necessary for the horses to do work each day in order to keep their leg muscles strong so they can support their body weight (1700 to 2000 pounds). Without those muscles, their legs would literally snap and the horse would collapse. Without fulfilling their purpose, they would destroy themselves.
Somehow I don’t this unique to horses.
