How do you adjust a horse?
The horse exhibits what is called the “stay apparatus”. It is a system of ligaments, tendons, and muscles that stabilize the joints in a standing position. This allows the horse to be on its feet for long periods of time, to stand with little muscular effort, and even sleep while standing. Because their back is in a naturally relaxed position, it makes it easy to palpate and adjust the spine.
I stand on a plastic “bale” (It is shaped like a bale of hay). This allows me to get mechanical advantage over the horse. 
With my hands, I then deliver the chiropractic adjustment. The adjustment is done to a specific area or joint of the spine. I stand on the bale for the withers, middle back, and low back. I adjust the neck and extremities while I am standing on the ground.
The adjustment can be done in an open area, arena, or large stall. I like for the horse to wear a halter with a lead rope. This is the safest way for me to adjust the horse.