The first step in the operation of shoeing a horse is to prepare the hoof for the shoe. As a rule the hoof is overgrown, and the farrier has to reduce it to proper proportions. He has also to produce a level bearing surface upon which a shoe can rest securely. The first question to determine is, what is the natural bearing surface of the hoof? On soft ground the whole lower surface of a hoof takes a bearing, because the ground yields, and allows the frog, sole, and lower border of wall all to take weight. On hard ground this is not so. The sole is arched, and on a level surface only rests on its abutment with the wall. If we examine the worn part of an unshod foot we find that the border of the wall, with a little of the sole to which it is connected, is marked by contact with the ground, and that the frog also shows evidence of wear. As a shoe is only to protect the hoof these parts are indicated as the natural bearing surfaces, and we follow nature in attempting to produce a similar surface by artificial means. With a rasp the farrier removes so much of the lower border of the wall as will reduce the foot to a proportionate form. He uses his rasp so that a level bearing is formed from the heel to the toe. He must leave as much horn on the foot as is necessary to protect it from injury, and he had better err on the side of leaving too much rather than too little. Some hoofs are so overgrown that their reduction with a rasp is tedious, and a layer of horn all round the circumference of the wall is more easily removed with a hammer and steel blade known as a "toeing knife". Properly used on a strong foot this method is unobjectionable, but on weak, soft feet it is liable to abuse by removal of too much horn. The whole of the superfluous horn must never be taken away with the "toeing knife", as it does not leave a level bearing surface. The rasp is to be used to finish the process, and as it only obtains a level by further removal of horn, sufficient must be left for it to work on. But a level surface is not the only aim a farrier has to keep in mind. It may be produced with such exactness that a level shoe rests on it perfectly, and yet the hoof may be altogether out of proportion. Both sides of the hoof must be left of the same height, and if the sides of a foot when it comes to a farrier be of unequal height, it is evident that one side must be reduced more than the other to obtain a proper form. Again, it is clear that if the foot be level on both sides, a man may rasp away more horn from one part than another and so cause a disproportion. Carelessness in the use of a rasp frequently leads to unevenness of the bearing surface. From the position in which a foot is held on or between the knees of a farrier, some portions of the hoof are more easily reached with the rasp than others. The left foot suffers by over-reduction of the outside and inside toe, the right foot at the inside heel and outside toe. A left-handed man is liable to injure feet in just the opposite positions. It is equally possible to over-lower both heels or only the toe. Even when the surface is quite even from heel to toe on both sides of the hoof, the foot may remain disproportionate. The heels may be left too high or the toe too long, and the proper adjustment of these two extremities of a hoof is the most difficult and most frequently-neglected part of the preparation of a foot. The great cause of difficulty is the fact that horses' feet are not of definite form, and that much harm may be done by attempting to carve a foot to some ideal standard.
Some feet have naturally high heels, which can only be reduced to a shapely pattern by weakening their structure. Some feet have naturally low heels, and some have long toes, which must not be interfered with (fig. 631). As a rule, when the overgrown wall is reduced to the level of the sole, very little more horn need be removed. The effects of lowering the heels are to lengthen the bearing surface backwards and to increase the slope of the wall in front. Too much horn at the heels tends to straighten the foot and to lift the frog from contact with the ground. It is always desirable that the frog should touch the ground, but when it is wasted no attempt to let it down by over - lowering the heels should be made.
Fig. 630. - Overgrown Foot.
ah, Old base of overgrown foot, ad, Level surface obtained by lowering the heel more than the toe. be, Level surface obtained by lowering the toe more than the heel, ce, Proper angle for new surface.
When a hoof is excessively sloped in front and the toe long, it would be injurious to shorten the toe by rasping the under surface of the foot. Such a hoof is properly treated by directly shortening the toe with a rasp applied to its border.
When a hoof presents broken horn on the lower border of the wall, it is necessary not to allow a shoe to rest on it. Broken horn cannot support weight, and when it yields may cause injury to the sensitive parts, and always causes shoes to become loose. Broken horn should be removed unless it can be left in a position offering no bearing for a shoe. When a foot is insufficiently covered with horn, either as the result of excessive wear from work without shoes or as the effect of previous removal by a farrier, great care is necessary to produce the best bearing surface. As a rule the quarters of a foot are most broken, and the heels may be trusted to take most bearing.
Fig. 631. - Well-proportioned and Ill-proportioned Feet A, Foot too long and heel too low. B, Well-shaped foot, c, Heel too high.
The sole should never be pared out with the object of making it concave and smooth (fig. 632). All that is necessary is to remove the loose flakes of horn which are naturally being exfoliated. No part of the sole will stand uneven pressure by a shoe, and therefore it must be lowered fully to the level of the wall. The border of the sole, just within the wall, may properly be used as bearing surface, but only in conjunction with the wall. Where the latter is broken away, no attempt should be made to use the sole as a support for a shoe. On flat feet care must be taken, especially at the toe, that the sole is not left unduly prominent. At the heels in all feet the angle of sole between the bar and wall should be left less prominent than the wall, or uneven pressure will take place and cause a corn. The old method of scooping out the sole of the foot till it presented a saucer shape not only left the horny covering too thin to protect the sensitive parts within, but it destroyed the bearing surface for a shoe by leaving the circumference of the hoof a mere narrow ridge. The bearing surface should be as wide as possible, and include not only the wall but the border of the sole.
The frog should not be touched. The broken and ragged portions invite removal, but are better left. They do no harm, and their removal nearly always leads to further loss of horn which is wanted.
The bars should not be cut away, but when they are very prominent may be so reduced that they take no direct bearing on a shoe except at the extreme point where they meet the wall. This extreme point of the bearing surface of a foot is very often injured. What is called "opening the heels" is a favourite operation with some men. It consists in cutting away a wedge-shaped piece of horn from each side of the frog and from the point of the wall. It is altogether evil in its effects, for whilst giving a delusive appearance of width to the heels, it robs the foot of some bearing surface and favours contraction.