Thoroughbred horses have historically poor quality feet and Dr. Scott Morrison indicates in Equine Disease Quarterly that the thoroughbred foot is light and lacks the mass for protection that is seen in heavier-boned breeds. The thinner walls and sole make the thoroughbred’s foot more susceptible to trauma, injury, and hoof capsule distortion, (which includes flaring of the walls, cracks, underrun heels, collapsed heels and sheared heels), all of which can lead to lameness. Since the heel region is designed to impact the ground first in horses to dissipate vibrations, the heel is usually the first area of the foot to display distortion because it is made up of soft and elastic structures.
The most common foot imbalance occurs when feet are shod with too much toe length and inadequate heel length. The center of the shoe’s weight-bearing surface should line up with the center of the coffin joint, which is aligned with the widest part of the sole. Balanced shoeing around the coffin joint helps to distribute force over the entire solar surface. The horse’s foot has the ability to handle large impact forces without collapsing and hoof capsule deformities develop slowly over time. Racehorses and other show horses spend 22 or more hours a day standing in a straw bedded stall, and Dr. Morrison believes this leads to most of the hoof distortions. Horses standing in a stall have little sole support, which over time allows fatigue of the hoof capsule. When horses are outside on the track or on other surfaces, the sole packs with dirt or sand and the sole is supported. Using temporary arch supports bandaged on to the feet when stalled, or heart-bar shoes, can aid in supporting the sole and help prevent hoof distortion.