The two most serious and permanent problems of the horse feet are laminitis and navicular disease. Laminitis is an acute inflammation of the laminae in the toe of the horse's foot. Usually, overeating causes the blood supply to change and the toe area to become inflamed and sore. Damage causes the toe not to grow as fast as the heel and the hoof takes on a sled shape. This chronic condition is called founder.
Horses are usually sorer when first exercised and become better when warmed up.
Hoof testers are used to detect sore or sensitive spots in the foot. This is even more critical if dealing with a breeding animal. Examine the horse's markings carefully and be sure that the registration certificate matches. The vet can help with this at the pre- purchase exam. The integrity of the breed is dependant on the fact that horses match their registered pedigree.