With a rasp form a level bearing surface for the shoe from heel to toe; keep both sides of the hoof of the same height; see that the length of the toe and the height of the heels are proportionate; let the frog and bars alone; remove from the sole only such portions as are loose or may receive undue pressure from a level shoe; finally run the rasp lightly round the circumference of the hoof, so that no sharp edge be left which is useless to support weight and might be broken.
Probably the earliest shoes fixed by nails to a horse's foot were thin iron plates, similar to those now used by Arabs and Turks. The nails were flat-headed, and so soon as the head wore off, the shoe would be loose. On grass land or soft roads this arrangement would afford a fair amount of protection, and the shoe would last a long time by merely refixing it with fresh nails. One of the first improvements would be to increase the thickness of the shoe, and to form the head of the nail so that it might be countersunk into the iron of the shoe and thus afford longer wear.
The great essential in all shoes is that they shall protect the hoof from wear and do no harm to the horse. They should be of sufficient substance to wear three or four weeks, and they should afford a good secure foothold on the surfaces over which a horse travels.
The best material for horse - shoes is undoubtedly good malleable iron. Steel is too hard, and favours slipping on stone pavements. Cast-iron is brittle.
Fig. 632. - A Pared-out Sole.
A shoe should be as light as possible, provided it affords four weeks' wear.
No shoe should be much more than half an inch thick, as the greater the thickness the more the frog is raised from a bearing on the ground. Very thick shoes render it difficult to make the nail-holes of the best size and form.
The older shoes were all made wide apparently with the idea that the sole needed protection. A weak, thin sole, especially when travelling over loose, sharp stones, may need some extra cover, but a sound sole which has not been robbed of horn by the farrier needs no protection from the shoe. The width of a shoe should depend simply upon the amount of iron necessary to afford four weeks' wear. If a narrow shoe wears out too soon it is better to distribute the additional amount of iron required in width than in increased thickness. A shoe should not be the same width throughout; it should be widest at the toe and gradually decrease towards the heels, as this provides the extra amount of iron where it is most wanted for wear.
A shoe has two surfaces - one applied to the hoof, the other for contact with the ground. Both may be quite flat, but there are conditions which govern the choice of form and render advisable some variations. The surface which is applied to the foot must correspond with the bearing surface on the hoof. On all sound, well-formed feet a shoe with a flat surface is the best. The foot surface of hind shoes is always made flat, as is that of narrow shoes for either hind or fore. So long as the sole of a foot is concave no uneven pressure can result from a flat-surfaced shoe, but when the sole is flat or convex there is danger of uneven pressure. Some front feet present this defect, and to provide a safe form of foot surface a shoe is " seated" (fig. 633). This means that the inner half, or more, of the foot surface is levelled so that bearing is confined to the flat outer portion of the shoe. This form of shoe is very commonly used, especially when the shoe is a wide one. Properly made, this foot surface is a safe and useful one. When the outer level portion is made too narrow, useful bearing surface is lost; when it is left a little wider than the wall it is unobjectionable. A very bad foot surface is formed by bevelling the iron so that it slopes from the outer to the inner circumference of the shoe (fig. 634). Such a surface affords no level resting-place for the hoof, and when it is attached to a foot may cause lameness by squeezing the wall inwards. At the heels the foot surface should always be left flat, and the seating of a shoe should cease about an inch or an inch and a half in front of the extremities of the shoe.
The ground surface may vary in form without affecting the foot in any way. The chief variations are such as afford some special means of increasing the security of foothold, and of providing against injury to the horse. A flat surface, broken only by a groove or holes for nails, is often used. Ridges or grooves are sometimes added for the special purpose of affording better grip of the road surface. Transverse grooves weaken a shoe and cause it to break more easily than longitudinal ones. What is known as Rodway iron is rolled in bars, having on the ground surface two grooves and three ridges (fig. 635). Into the outer groove the nails are driven. No better form of shoe exists for harness work, provided it affords the necessary wear; but this is just where it fails for the heavier class of horse.
Fig. 633. - A "Seated" Foot Surface.
Fig. 634. - A Bad Foot Surface.
Fig. 635. - Rodway Iron Shoe with Double Grooves.
Fig. 636. - A "Concave" Ground Surface.
The hunting-shoe is concave on the ground surface, with a groove for the nails round its outer border (fig. 636). This is a good form for hacks and other light horses, as it affords very firm foothold, especially upon the grass and soft roads.
"Calkins" are the turned-down extremities of shoes, which would probably be called heels by non - horsey folk. Projecting as they do from a half to one inch, they afford the most effectual stop or catch where the surface is such that they can sink into it. For the hind shoes of hunters they are quite indispensable, and they are most useful for other classes of horse on soft roads. On some paved streets, where the stones are set with a space between them, calkins afford the best foothold, but on hard, smooth surfaces, such as asphalt, they are quite useless. To provide against wear, calkins are often made too high. Excessive height can be avoided by making the calkin square, and so providing for wear with a lower projection. The evils of calkins are that they put the foot out of its normal position by raising the heel. Thus the toe is subjected to disproportionate wear, the frog is kept from contact with the ground, and to some extent the muscles of the limb are placed at a disadvantage for action.
In Scotland and the north of England heavy horses are shod both fore and hind with calkins and toe - pieces. This form of ground surface on a shoe has some advantages for horses that only work at a walking-pace and have heavy loads to move. The toe-piece consists of a portion of a square bar of iron welded across the toe of a shoe. This, with calkins, makes the shoe more level, and so preserves the proper relative position of foot to limb. The toe-piece affords foothold to the front of the shoe just as calkins do to the back of it, and the combination enables a lighter shoe to be used. It is a good system for railway shunt horses and for animals dragging heavy wagons over paved streets, if the paving-stones have spaces between them in which the toe-piece can find lodgment.