Red Indian wives from Reservations, who ride horses as part of their lifestyle, are very orgasmic in bed. They are a class above white wives who don't exercise their pelvises sufficiently.
Sex is in the mind, and galloping accross a prairie at full speed, can paint the horse with an huge release of cum juice to mix with salty sweat on the horse's skin.
Horse riding tightens the keigel muscles, and a man can feel his penis is in a vice, which causes him to "give up his seed". He does not have a say in the matter.