If in the shortening of the wall a part is from ignorance left too long, or one-half of the hoof shortened too much in relation to the other half, the foot will be unbalanced. The horse will then touch the ground first with the section of wall which has been left too high, and will continue to do so until this long section has been reduced to its proper level (length) by the increased wear which will take place at this point. In unshod hoofs this levelling process takes place rapidly; such, however, is not the case in shod hoofs, for here the shoe prevents rapid wear, and, indeed this levelling process is often rendered impossible through the welding of high steel calks to the shoe. If this fault in trimming be repeated at the next and subsequent shoeings, and if the faulty relation of the ground-surface of the hoof to the direction of the foot-axis remain during several months, the portion of wall left too high will grow more rapidly, the walls will lose their natural straight direction and become bent. If, for example, the outer wall has been left too long during a considerable period of time, a crooked hoof results (Fig. 85) in which the rings are placed closer together upon the low (concave) side than upon the high (convex) side. If for a long time the toe is excessively long, it will become bent; or if this fault affects excessively high quarters they will contract either just under the coronary band or will curl forward and inward at their lower borders. These examples are sufficient to show both the importance of the manner in which a horse places his foot to the ground and its influence upon the loading, growth, and form of the hoof. [Illustration: FIG. 85. Crooked (right) fore-hoof.] Wear of the Shoe and of the Hoof upon the Shoe. The wear of the shoe is caused much less by the weight of the animal’s body than by the rubbing which takes place between the shoe and the earth whenever the foot is placed to the ground and lifted.