Remember that the chiropractor is not trying to move and entire horse, but rather a specific joint in the horse’s spine.  Every joint has sensitive nerve receptors which send messages to the brain.  The adjustment, a high velocity, low force thrust by hand, stimulates these nerve receptors.  To be successful the adjustment is applied to a specific joint in a specific direction.  The adjustment restores normal motion in the joint and alleviates muscle spasm and pain.