A thick shoe raises the foot from the ground and thus removes the frog from bearing—a very decided disadvantage. It also requires the larger sizes of nails to fill up the deep nail holes, and very often renders the direction of the nail holes a matter of some difficulty.
The width of a shoe may beneficially vary. It should be widest at the toe to afford increased surface of iron where wear is greatest. It should be narrowest at the heels so as not to infringe upon the frog, nor yet to protrude greatly beyond the level of the wall. The thickness of a shoe should not vary unless, perhaps, it be reduced in the quarters. Heel and toe should be of the same thickness so as to preserve a level bearing. Excess of thickness at the toe puts a strain on the back tendons, whilst excess at the heels tends to straighten the pastern.
The surfaces of Shoes. There are two surfaces of the shoe which claim attention, one which is applied to the foot, and another which rests on the ground. The form of these surfaces may be varied greatly, but of course the foot-surface presents much less necessity and less opportunity for alterations than the ground-surface. The foot-surface of a shoe must be formed in accordance with the requirements of the horse's foot, and no other consideration should be allowed to materially modify it. The ground-surface may be altered to suit the tastes and prejudices of the owner as well as the requirements of the horse and the peculiarity of roadways.
Fig. 32.—A level, flat bearing-surface.
The Foot-Surface. It is quite obvious that the surface of the shoe upon which the hoof has to rest should be regular and even; that it should not consist of hills and holes or grooves and ridges. I should not have mentioned such a very evident matter but that in large towns, the cheaper and poorer classes of shoeing commonly possess this very fault. When shoes are made from thin, wide, old iron tyres they are "buckled" on one surface, and to hide this the farrier puts that side to the foot so that it is not noticed until it causes damage. There are three or four forms of foot-surface adopted by farriers, all of which have distinctive features, and some of which have very grave evils. There is the plain flat surface which is given to all narrow shoes, to hunting shoes, and to some heavier and wider shoes. So long as the sole is healthy and arched this is a very good form. All hind shoes have a flat foot-surface, and most fore shoes might have it with advantage. It utilises the whole of the natural bearing surface, and must of necessity afford a firmer basis for the foot to rest upon than a more limited surface. The fore feet are not so constantly arched in the sole as the hind. Sometimes they are flat and occasionally convex. If a shoe be intended for use on all feet—on feet with convex and flat soles as well as those properly formed—a wide flat foot surface would often cause injury by pressing unevenly upon the sole. To avoid this injury in less than five per cent of feet, and to save the trouble of keeping in stock shoes of different forms, the flat foot-surface of front shoes has been replaced by a bevelled or "seated" surface. ([Fig. 33]).
Fig. 33.—A "seated" bearing surface.