Another fault results from holding the rasp untruly. If we suppose the inside heel of the near foot to be under preparation and the farrier inclines his rasp too much inwards, he leaves the wall at the heel lower than the sole within it. On such a foot a level shoe rests upon the sole instead of upon the wall, and a bruised heel soon follows.
Paring away the sole to produce a deep concave appearance has another evil effect in addition to that before pointed out. It removes the horn just within the border of the wall, taking away the natural support, and leaving as bearing surface for a shoe a narrow ridge instead of a strong flat surface. [Fig. 31] shows this fault, and it must be remembered that this ridge may be left as thin as a knife edge. Such a ridge cannot sustain the weight of the horse, and when it yields the shoe also yields, the clenches are raised and the shoe becomes loose.
Fig. 31.—A Pared-out Sole.
Excessive rasping of Wall. The best farriers—those most proud of their work—have a great temptation to use a rasp too freely to the outer surface of the wall. The hoof gets rough, or it may be ridged, its appearance is improved by being made smooth, and it is only human to turn out work which is clean and neat. Owners and grooms are rather inclined to forget the claims of the horse when judging shoeing, and the result is that some harm is done by excessive rasping. A strong foot does not suffer much, but its strength is preserved by leaving the hard outer surface intact. Rasping off an outer layer of horn favours evaporation and hardening of the underneath layer, and the toughness so desirable is to some degree replaced by hardness and brittleness. Excessive rasping below the clenches is even more injurious than rasping above them. The wall, between its bearing surface and the clenches, has to withstand the contact of the shoe, and the perforation by nails. It should be the toughest and strongest part, and, therefore, should not be rasped more than is necessary to lay down the clenches and finish the fitting. Unfortunately the neatest work is done by fitting a shoe "close" and then rasping off any protruding horn. This is bad for the foot, as it weakens the wall and spoils the bearing surface at each shoeing. The worst offenders in this direction are dealers, who sacrifice everything to appearances and insist upon shoeing being neat at all hazards.
Opening the Heels is one of the gravest faults a farrier can be guilty of. It consists in cutting away the extremity of the wall at the heel and generally a slice off the side of the frog at the same time. The effect is to produce an appearance of width at the back of the foot—to make what is called "a fine open foot." [Fig. 31] shows a foot which has been injured in this way. The wedge shaped opening which results has many objections. It breaks the continuity of structures at the heels, it removes horn unnecessarily, it weakens the foot and, when the wall is interfered with, it shortens the bearing surface for a shoe. The bearing surface at the back of the foot is perhaps the most important of any afforded by the wall. The longer the bearing surface is at the heels the more the base for sustaining weight is brought under the leg, and the better the position for supporting the body. All removal of horn that shortens this surface is injurious.
Over-reduction of hoof is always a fault. It is true a carefully fitted shoe on a foot so treated may do no harm for a time. Too much horn should be left rather than too little. A strong covering of horn is a protection against many mistakes in the fitting or form of a shoe applied to a foot. So long as a hoof is everywhere strong enough to sustain pressure and afford bearing, weight is evenly distributed throughout the whole foot. When the horn is thin it yields to any uneven pressure and damage is done to the foot, even if immediate lameness is not induced.