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The coffin bone is suspended inside the hoof capsule by the lamellae and surrounded by the blood- filled corium. When the hoof is picked up off the ground, the hoof capsule is smallest and exerts pressure on the corium, thus emptying it of blood (ie. pumping blood upwards, supporting the heart). On bearing weight, the hoof capsule expands, the coffin bone descends and the sole spreads outward/downward. As a result of this, the corium has more room (compare 5 mm to 2-3 mm when not bearing weight) and can, like a sponge, fill with blood once again. When the foot is picked up, the whole cycle repeats. Thus, with every step, the hoof pumps blood back toward the heart. This pumping action is vital for optimal waste/nutrient exchange within the tissues of the hoof, and supports the entire circulatory system.
Aside from this, the hoof is responsible for shock absorption. This takes place through the expansion of the hoof capsule and the spring-action of the suspended (not fixed) coffin bone. In addition, the hoof contacts the ground first with the softer areas (frog and bulb of the heel), adding additional shock absorption.
These vital functions of the hoof are severely disrupted through the use of shoes. An expansion of the hoof upon bearing weight becomes virtually impossible, since the hoof does not expand only in the last third, but all the way from the toe to the heel. As a result of this, the hoof receives only inadequate blood supply and circulation, which leads to poor horn quality. The ability of a horse to feel pain (or anything, for that matter) in the foot is greatly reduced, since the nerves in the hoof receive insufficient oxygen. With shoes, the hoof no longer impacts first on the softer shock absorbing material of the frog and bulb of the heel, but strikes the ground with hard, unyielding, non-shock absorbing metal. In 1984, the Swiss Cavalry, at the veterinary medical faculty of the University of Zurich, contracted research into the effect of shoeing. Studies showed that the impact force a shod hoof receives on hard ground is 10-33 times that of an unshod hoof. The vibrations set up in the hoof by the vibration of the metal shoe is approximately 800 Hz, compared to "only" 150 Hz with a rubber shoe. However, shock absorption and pumping action can also be insufficient in an unshod horse, when the shape of the hoof is deformed (improperly trimmed) and/or the hoof is too dry, and thus no longer elastic.
With friendly permition by DVM H. Strasser
Copyright 2005 Dr. vet. med. H. Strasser
Ed & Trans. Sabine Kells
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