1. Empty out your stable
2. When the horse that you wish to breed is at 35% or higher, put it in your stable. This will make your horse stable ready to harvest
3. Insert Stallion or Wandering Stallion
4. harvest your horse stable
Hopefully something like this will appear on your screen
This method of breeding allows you to harvest your horse stable multiple times a day. You should try to have 10 or more horses ready ( 35% or higher ) in order to increase your chances of getting a foal. If you do not get a foal you will either get coins, farmhands, arborists, or 100XP.