@edgarblythe,
I have followed Monty Roberts' observations regarding the social structure of horse herds. A mare is at the top of the hierarchy of a horse herd and enforces the rules of the herd. Any other horse that acts out contrary to the safety and order of the herd is punished by temporary exile from that herd. This is a very scary and dangerous position for a horse to be in because they are prey animals and are very vulnerable on their own.
Monty Roberts has shown that a human can replace the mare as the top of the hierarchy. If there is just a single horse and a single person, the pair constitutes the herd, and the horse wants to comply to the wishes of the person for its own safety and security.
Therefore, training a horse does not have to involve force and brutality because the horse wishes to comply.
Zebras, apparently, don't form social hierarchical herds as horses do