Getting a new horse is an exciting occasion, but if you simply turn it out with its new pasture mates, its get-acquainted experience could end up providing more excitement than you bargained for. Horses have a definite pecking order, and their process for sorting out who dominates who can include anything from squeals and chasing to biting and kicking. With some patience and planning, you can help your new horse make a smooth and safe transition from newcomer to pasture buddy.
Release your new horse by itself into a corral with walls/fences that are secure. Provide food and water.
Turn your other horse(s) into an adjoining pasture/corral where they can touch noses with the newcomer, but cannot injure themselves if they paw or kick at each other through the fence.
Stand back and let them introduce themselves. Horses will squeal, paw, pin their ears back, toss their manes, bite, kick, run--all aspects of normal behavior to determine who is dominant. Observe, but do not interfere.
Monitor the get-acquainted process for several days or up to a week or more. Resist the temptation to turn your new horse out with the others before they’ve accepted it. Wait until biting, squealing, and other aggressive behavior reaches a level normal for your existing herd and the horses seem comfortable across the fence from each other.
Alternate pasture time for several days. Turn your new horse out alone in the same field your herd usually grazes in so it can get acquainted with its new surroundings and leave its scent behind without having to interact with the herd.
Turn your least dominant horse out into the pasture with the new horse. Allow these two to become well acquainted and comfortable with each other over the course of several days.
Introduce the next least dominant herd member to the pair. There may be some squealing and “sorting” behavior again, but it should be short-lived and half-hearted as further bonding takes place. Repeat with each subsequent horse until all are integrated and you are confident that the new horse has found its place in the hierarchy.