Smacking, enthusiastic slaps, patting HORSE is not perceived as a reward by the horse
Andrew McLean, horse behaviorist/psychologist and co-author with Paul McGreevy of the book, EQUITATION SCIENCE, advises that if humans want to give a “feel good” touch to their horses, they should do what horses do to each other, which is to lightly scratch the horse at the shoulder, just below the withers. What horses do when they are relating in a friendly way is to gently scratch each other on the shoulder with their teeth. Next time you succeed at that next competition, lean over (rewarding the horse by loosening the reins) and gently scratch the base of your horse’s neck.
Caveat:
FYI especially for the huggy smoochy humans…be careful where you touch a horse, especially stallions and many geldings. The male horse’s sexual arousal spot is in front between his legs at and under his chest; it’s the male horse’s masturbation spot and the spot which rubs against the mare when the male mounts her. I did some reading & research on how humans (predators) should handle horses (prey animals) which is how I stumbled upon this information.
While I’m on the subject of patting animals…dogs really, really do not like to be patted on the top of their heads, however gently the human does this. They will tolerate it, because it’s in their nature to please the humans they are bonded to, but if you want to please a dog, scratch him behind the ears.