There is no sign that horses wore boots or leg protective devises to support the legs throughout the greater part of equestrian history. The first boots were seen in America in connection with harness racing which was established early in the 19th century. The use of these early boots became the basis for the design of modern boots. As competitive disciplines increased in popularity new designs and materials were introduced. Leather and felt were generally used until recently when PVC, neoprene and other synthetic materials became popular because of their ability to absorb impact and their ease of maintenance. The prime reason for the use of boots are to protect and support the horses ligaments and tendons. Which will reduce the possibility of sprains and strains. Tendon boots are specifically designed to support the flexor tendon running down the rear of the cannon. Splint boots protect the splint bones which are quite fragile. There are also overreach boots, brushing boots, bell boots, open front jumping boots, hock boots, shoe boil boots,  knee and ankle boots, poultice boots and shipping boots, Bandages can be made of poler fleece which is used to make polo bandages, cotton, elastic and even synthetic fleece. The point is that a horses legs are fragile and need to be protected.