Prognosis.—This will depend upon the age, kind, and location of the crack. A low crack is without significance unless it is the remnant of an old coronary crack which has grown down. Coronary cracks, on the contrary, are more serious because of the lameness which often accompanies them, and especially on account of the long duration of the healing process.
The borders of the crack never grow together, and healing can only take place through healthy, unbroken horn growing down from the coronary band.
(a) Treatment of Coronary and Bar-Cracks.—If practicable, allow the affected horse to go barefoot; otherwise, the use of the bar-shoe for all cracks is advised, because it will continuously protect the diseased section of wall from pressure by the shoe. If there are present still other diseases of the hoof (corns, contraction, flat or full hoof), the addition of a leather sole with packing will be most beneficial, not only in favoring the healing of the crack, but also in improving the form of the hoof and in favoring the cure of the other lesions. In all coronary cracks it is of advantage to assist healing by fastening or immobilizing the borders of the crack by one of the following methods:
1. By rivets (nails), which pass across the crack through holes previously drilled in the horn ([Fig. 217]).
2. By clamps or hooks, which by means of special pincers are forced into pockets previously burnt into the horn on opposite sides of the crack ([Fig. 219, B]).
3. By a thin iron plate placed across the crack and secured by small screws, such as are used in wood ([Figs. 220], [221]).
4. By means of a bandage to last one shoeing.
Toe-crack occurs most often in draught horses and most frequently in the hind feet. In shod hoofs it starts at the coronary border, and unless proper treatment is instituted soon reaches the plantar border. Long toes and low quarters and excessive dryness of the horn are predisposing causes. The exciting cause is usually forward pressure of the upper end of the short pastern against the thin upper edge of the wall of the toe. In the last part of the phase of contact of hoof with ground the pasterns are upright, or may even incline downward and backward (foot-axis broken strongly backward), the short pastern presses the coronary band firmly against the upper thin edge of the toe, when if brittle through dryness it is unable to stretch and tears asunder. Thus, under the effort of starting a heavy load, when a horse with all four legs flexed has risen upon the points of his toes, a short quick slip followed by a catch, will frequently start a crack at the coronet.
The hoof should be so dressed and shod that the foot-axis shall be straight when seen from the side. In hind feet it is admissible to break the foot-axis slightly forward. Therefore, shorten the toe and spare the quarters. If the latter are deficient in length, raise them by swelling the branches or by low heel-calks.
Fig. 217.