The Art of Horse-Shoeing: A Manual for Farriers

by William Hunting

Growth of Hoof.

Like every other part of an animal body, the hoof is constantly changing. Wear and tear cause waste of the horn, which is replenished by growth. When wear exceeds growth the foot becomes denuded of horn, and lameness results. When growth exceeds wear the hoof becomes disproportionately long, and some parts suffer by the overgrowth of others—for instance, whenever the heels are unduly high the frog becomes small and weak. In a state of nature the horse's foot keeps itself of proportionate form. On hard ground the hoof is worn away as quickly as it grows. On soft ground it may, for a time, become overgrown, but this is rectified by the soft horn becoming fractured and broken off. In enclosed cultivated grounds the movements of the horse, even on grass land, are too limited to ensure a proportionate form of hoof. When horses are turned out without shoes the feet should not be left to take care of themselves, unless the pasture is of large area and the time at grass extends for several months.

In a hoof which is overgrown—and all shod feet become overgrown in four or five weeks—there is apparently a greater excess of horn at the toe than elsewhere. This is due to the oblique direction of the wall at the toe, and to the fact that the horn fibres of the hoof do not grow down vertically, but obliquely forward. When the natural wear of the hoof is prevented, the effect of growth is to lengthen the toe and carry forward the bearing surface of the foot. Now this bearing surface has a proper relative position to the limb above it. Therefore a disproportionate foot must injuriously affect both the action and position of the whole limb.

The rate at which the wall grows varies greatly in different horses, and is affected by external conditions. The good average wall grows nearly one inch in three months, and the whole hoof is replaced in from ten to fifteen months. The hoof grows more rapidly when a horse is actively exercised than when he is confined in a box. Febrile diseases check growth, and irregularities of the system cause the formation of ridges in the horn, each one commencing at the coronet and being carried down with the growing horn until the hoof is marked by a series of rings running transversely and parallel to each other. These rings are of themselves no detriment to a horse, but they mark irregularities of growth which may have been due to illness or lameness.

The growth of horn on a shod foot is affected by the bearing it takes. When a part of the wall takes no bearing on the shoe it grows quicker than that which does. We see this when a shoe is so fitted that the heels take no direct pressure on the shoe, also when a portion of wall is broken at the quarters, and again when, for any reason, a portion of the edge of the wall has been rasped away to prevent bearing upon some special spot. In all these cases, after the shoe has been worn a month, it will be found that the horn has grown more rapidly at the part where bearing did not take place, and, when the shoe is removed, the horn which was relieved of pressure is found to have been in apposition with the shoe.

The growth of horn cannot be accelerated by any application to its surface. If we desire to hasten growth of the wall we can do so by stimulating the part from which it is produced, i.e., the coronary band. A mild blister to the coronet causes considerable increase in the rapidity of growth, but no ointments applied to the surface of the wall affect its production in the least, though they may modify its condition and prevent dryness and brittleness.

The sole grows in much the same way as the wall, but it wears quite differently. It never becomes overgrown to the extent seen in some instances of the wall. The hard firm structure of the wall, if not worn down by friction on roads or dry hard surfaces, may grow to a great length. As a rule, when much overgrown, it splits in the direction of its fibres and becomes detached in broken fragments. The sole, when overgrown, has a tendency to become detached in flakes, and never very much exceeds its normal thickness without becoming dry and brittle, when the movements of the horse cause it to break up and fall off.

The frog when it takes a bearing on the ground wears off in shreds. A frog which takes no bearing dries up, and sometimes a large superficial layer is cast off. Though the softest of the horny divisions of the hoof, the frog is able to withstand wear and tear as well as any of the others. Being elastic and resting upon soft tissues, it is able to yield to any undue pressure and leave the firmer horn of the wall and bars to sustain the greater strain. The growth of the frog depends a great deal upon the form of the back parts of the wall. If the heels become overgrown, the frog is removed from bearing and consequently wastes. High heels have always between them a small frog. On the other hand low weak heels have always a large frog, and the explanation is that the increased bearing thrown on the frog causes greater development.

Properties of Horn. Horn is light, hard, tough, and elastic, properties most essential to its usefulness as a protector of the foot. Horn is porous, and absorbs moisture. Too much moisture in horn weakens it, and therefore it must be remembered that the natural protection against this is the hard outer layer of the hoof. When this layer is rasped off moisture is more easily absorbed until the dry, hard surface is restored by exposure and friction.

Horn is a bad conductor of heat, and thus an equally good protective against the effects of snow in some countries, and of hot dry sands in others. With a sound thick hoof the application of a red-hot shoe produces very little effect on the internal structures, provided, of course, it remain in contact only a reasonable time. With a foot protected by a thin layer of horn, fitting a red-hot shoe must be done quickly or it may damage the soft tissues.