Fig. 20.—A disproportionate hoof—heels too high.
Fig. 21.—A disproportionate hoof—heels too low.
Now these alterations in both cases affect not only the form of the foot but its relative position to the leg, and as the bones of the limb above are a series of levers connected by muscles and ligaments so placed as to be most efficient for movement, it is evident that alterations of the foot must affect the action of the limb. (Compare [Figs. 19], [20] and [21]) In the unshod horse roaming about there is a natural automatic return to proper relative position whenever it has been temporarily upset. A long toe is worn down and high heels are reduced to their proper level by friction. Not so a foot protected by an iron shoe. Wear is stopped, and a disproportionate hoof becomes more and more disproportionate. Temporary alterations of the position of the foot do little harm because they are permitted, within a margin, by the movement of joints and by the elasticity of muscles. When, however, an alteration of position is continued for many weeks it tends to become permanently fixed and may thus do a great deal of harm, which is not traced to its real cause because the effect is slow and gradual. It is important, therefore, to remember that the proportion of the hoof is to be maintained not only because it is necessary to the well-being of the foot; but because it affects the action of the whole limb. Too long a toe may cause a horse to stumble, and it must always increase the strain on the back tendons during progression. Heels too high prevent the frog from taking its proper bearing on the ground, and thus cause a loss of function in the back parts of the foot. An excessively high heel has a tendency to throw the knee forward and to straighten the pastern.
Fig. 22.—Heels high—under surface and side view.