wild horses

a wild goose never laid a tame egg

Most things are inherited and predetermined.

change horses in midstream

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

drive a coach and horses through

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

go wild

To become very noisy and excited.

hold one's horses

To be patient; to wait.

horses for courses

Different people are suited for different jobs or situations; what is fitting in one case may not be fitting in another.

run wild

To go unchecked; to be out of control.

sow one's wild oats

To spread one's genes around by impregnating many females.