It sometimes happens that one foot is smaller than the other from birth, and where this is known to be so, too much importance must not be attached to it; but it must not be forgotten that such cases are exceedingly rare, and it becomes necessary, without direct knowledge to the contrary, to regard all differences of this kind to have resulted from disease either in the organ itself or in some remote part, necessitating prolonged resting and contraction of the foot as a result.
The fact must not be lost sight of that one or both feet may be considerably reduced in circumference by breakage of the horn or undue paring, and disparity of size may be due to one or other of these causes; here, however, the heels will be open, and in point of width and development correspond with the larger foot. We shall see presently that contraction of the foot resulting from disease is attended with certain well-marked changes which are not difficult to recognize, and which clearly indicate the existence of unsoundness.
The feet may be unduly flat or too deep and upright, as the result of disease, laminitis or fever in the feet being a common cause of the former, and navicular disease, or some more remote affection in which the foot is rested, of the other.
Where laminitis has existed, the hoof usually presents a number of ridges encircling the foot, the hoof-horn is brittle, dry-looking, and coarse in texture, the heels are low, the toe thick, and in some cases the sole is more or less convex and the front of the hoof concave or sunken. In the morbidly upright deep feet the texture of the horn is close and compact, and the hoof presents a dense solid appearance. This is especially the case in navicular disease, where the sole is very concave, the heel narrow, and the frog wasted. Where these characters exist there can be no doubt as to the animal's unsoundness.
Careful search should at all times be made for cracks in the hoof, or, as they are termed, "sandcracks" (Vol. II, p. 3GG). These ruptures of the horn occur in various situations, in some of which they are not at once apparent. This is very much the case where they are of limited extent and occupy the upper border of the hoof hidden by the overhanging hair. In the lighter breeds of horses this accident is most frequently seen on the inner quarter, while in draught-horses it is more often noticed in front of the hoof; wherever they occur, they represent a serious form of unsoundness, serious not only on account of the long period required for their treatment, but also because of their liability to recur. The examiner should be on the alert here, for unscrupulous dealers do not hesitate to fill the cracks with composition, and the artful way in which it is done renders deception possible unless the greatest care is observed.
A defect, which in some instances must be included in the category of unsoundness, is that comprehended in the term "shelly feet", by which is understood a dry and brittle condition of the horn, which, being also loose in texture, splits and breaks on the slightest provocation, rendering shoeing difficult, and sooner or later impossible.
Another defect in the horn, to which unsoundness attaches, is that condition of the crust known as "false quarter". Here there is a local deficiency of development in the hoof arising out of an injury to the coronet, in which the horn-secreting band has been to some extent destroyed and the hoof weakened. It is recognized by a deep wide furrow passing from the top to the bottom of the hoof.