Standardbred racehorses wear bandages both on and off the race track for a variety of reasons. They are used as a means of support and protection.
Many trainers will use brace bandages on their trotter's hind legs. Brace bandages offer light protection for a horse that doesn't hit his shins or just barely brushes them, and at the same time permits the horse to trot lighter than if he was wearing a protective boot made out of leather or a synthetic material.
Brace bandages also tend to widen out a trotter's gait behind, and especially help in the case of a "line" gaited individual. A "line" gaited trotter carriers his legs on the same side in a direct line when viewed from the front or rear. In contrast, a "passing" gaited trotter moves by placing his hind leg slightly outside of the front leg when viewed from the front or the rear. Obviously, a "line" gaited horse would be more likely to interfere, and thus require protection for the hind legs.
Bandages used on the front legs generally are used for support, often times with horses that have old tendon injuries. Sometimes bandages are used beneath protective boots. Many times trotters will wear brace bandages behind, and a boot will be placed over top of the bandages for added safety when a horse interferes with that area severely.
After a race is over and the horse is bathed and either walked or left to cool out in his stall, he is often times "done-up" in standing, or stall bandages. These are thicker and offer more support than the brace bandages, and their purpose is to support and protect the legs while the horse is resting in his stall.
In nearly all cases, a layer or two of cotton is placed beneath the standing bandages. Once the cotton is in place, the leg is bandaged. Standing bandages usually come in three-yard lengths and run from the pastern up to just below the knee or hock of the horse. The cotton will protrude slightly at both the top and bottom of the bandage.
Not all horses that race are bandaged for their stall rest. Of those that are, some are bandaged only in front or only behind while others are bandaged all the way around. Many times bandages help to facilitate the action of any leg brace, liniment or other preparation being used beneath them. They do not necessarily indicate that the horse is unsound in any way, and some horses that are perfectly sound are bandaged all the way around.
Other horses who have shown indications of developing leg troubles are bandaged, as the trainer believes it would be in the best interest of maintaining the horse's soundness.
Extreme care is taken when bandaging a horse's leg. Joint areas, such as ankles, can stand a lot more pressure than tendon areas. Bandages should therefore be more firm around the ankle than around a tendon. That is why many trainers have their groom use a thick padding of cotton under bandages, to insure the bandage won't become too tight in a critical area.
It is just as important that bandages are not applied too loosely, because the primary reason for the bandage is to lend support. Also, a loose bandage is often a great source of fun for some horses, because they enjoy chewing on them and pulling them. Unfortunately for the horse, if he pulled the loose bandage taut, it could cause severe damage to the tendon area, possibly ending his racing career.