Ok, when your horse is full grown, make it go in between the little holding pen in its stall, and the hay. not in the holding pen. then go in the holding pen thing yourself, and go to the side where your horse is, and press A like your getting on. you will get on your horse and he will go through the fence! i just think thats really funny.
also have you ever noticed that the harvest sprites are kinda like jesus because they always walk on water???