It becomes necessary now to examine further the foot, more especially as to its ground surface. Having observed the width of the heels, the examiner lifts it up, and so brings the sole and frog under observation. In a normal condition the former should describe a gentle arch upward. Any extreme concavity must receive careful consideration. It may be due to an overgrowth of the crust being permitted in the course of shoeing, but it is frequently the result of contraction of the wall consequent upon some deep-seated trouble, such as navicular disease.
Confirmation of this will be found in a shrunken frog, a thick, solid, upright, blocky-looking hoof, and more or less obvious lameness. Some degree of hollowness or undue concavity of the sole will arise from many causes which have led to the foot being rested for a long period, and which of course must be associated with unsoundness. It must, however, be pointed out that where, as a consequence of indifferent shoeing, the crust is permitted to remain too deep or to project too far beyond the sole, the latter will have the appearance of being too concave, and may be actually so. Whether it is or not is a matter for the examiner to decide from the general appearance of the organ.
The frog will claim attention now. It should be free from thrush and canker. A good, wide, deep, bold frog is much to be desired. A small, dry, shrunken frog is an object of some suspicion, especially in aged horses, where it may be associated with navicular disease, or some ailment for which the foot has been rested. Although not an unsoundness in itself, it is an indication significant of disease elsewhere, and calls for careful consideration. Thrush in its milder form, when unattended with lameness, does not constitute unsoundness, but where the sensitive frog is much exposed it must be so considered.
In those cases where the frog is broken and ragged the detached portions should be removed, and the general surface of the organ inspected for underlying disease.
Canker which appears in the form of a fungating growth about the frog or sole, or both, attended with an offensive discharge, is one of the worst forms of unsoundness.
The sole may be too flat, but, as a natural conformation, will not come under the category of unsoundness unless identified with lameness; it is nevertheless a sign of weakness, and horses with flat soles are never a desirable purchase.