Ponyplay
Absolutely Kink is Ponyplay!
Being held by your owner as a ponyboy/ponygirl is a wonderful humiliation. Acting out the role in front of an audience, performing tricks and trotting on the reins can be delightfully humiliating. The bridle or a gag effectively prevents any contradiction. The nice leather or latex that a pony may wear flatters the skin.
The owner can train his human ponyboy or ponygirl as he wishes, he can bully it, whip it or sexually stimulate it with a butt plug with a tail or nasty clamps on its nipples.
The king's discipline in pony training is certainly the "sulky". Harnessed in a fence, the pony is allowed to pull its owner's sulky while the owner can whip it meanly at every opportunity as punishment for "wrong" steps or too less speed....