I could eat a horse

beat a dead horse

To persist or continue far beyond any purpose, interest or reason.

bite to eat

A snack or quick meal.

change horses in midstream

To change one's plan or approach when an effort is already underway or at another inopportune time.

charley horse

A muscle cramp, usually a strong one, in the thigh, leg, arm, or core.

close the stable door after the horse has bolted

To attempt to prevent a problem that has already occurred; to design and implement a preventive mechanism that is too late (after the first failure instead of before).

dark horse

Someone who possesses talents or favorable characteristics that are not known or expected by others.

don't shit where you eat

One should not cause trouble in places, groups, or situations that one holds as important or necessary to one's happiness or well-being.

drive a coach and horses through

To spoil, break or render ineffective (a rule, plan or agreement).