spawning a horse using command blocks spawns the horse you want on top of another horse minecraft. I ran the command: /summon minecraft:horse ~ ~ ~ {Variant:0,Passengers:[{id:horse,Variant:769,SaddleItem:

,ArmorItem:{id:iron_horse_armor,Count:1},Tame:1,Temper:0,OwnerUUID:d8eee57d-5919-4b1a-b1b3-7088ba0ff72e,Attributes:[\{Name:"generic.maxHealth",Base:24.0F},\{Name:"horse.jumpStrength",Base:0.8F},\{Name:"generic.movementSpeed",Base:0.3F}]}]}