This is a malignant disease of the feet characterized by the development of a soft, spongy growth on the frog or sole, or both, attended by a thick, offensive discharge of the consistence of soft cheese. It is more common in the heavy than the light breeds, and in the hind than the fore feet. The disorder may be confined to one foot alone, or it may affect two, or all of them may suffer. Pathologically, it is essentially a papilloma or overgrowth of the papillae of the sensitive foot, and in this respect is allied in its nature to grease, by an extension of which from the leg to the foot it is sometimes produced.
The inducing causes are such as provoke irritation in the sensitive foot, hence it commonly follows upon an attack, or more frequently upon a succession of attacks, of "thrush". It may also arise out of various forms of injury to the foot, as corns, pricks, sand crack, and quittor; and, as already remarked, it sometimes results from the downward extension of grease in the heel. By some it is regarded as a specific disease, and this may ultimately prove to be the case.
A grayish-white offensive discharge, very much like what is seen in thrush, is the first indication of the disease. This is accompanied by a soft, spongy swelling of the sensitive frog or sole, in the course of which the horny covering becomes broken up into coarse, brush-like fibres, having no disposition to cohere and form sound horn (fig. 398). Later, the horn-producing power of the affected parts becomes enfeebled and ultimately destroyed, and a thick fleshy growth appears, covered with enlarged papillae and a stinking mass of degraded horn cells (fig. 399). Unless arrested, the disease spreads from the horn-denuded sole to the heels and quarters until the foot becomes stripped of its hoof and greatly disorganized. In the early period of the disease, and even when it is considerably advanced, lameness may be altogether absent or very inconsiderable, and the slow progress of the malady enables horses affected by it to continue in work for some time; but as the foot becomes more and more bereft of its horny covering, pain and lameness increase until the animal, though otherwise healthy, is rendered unworkable and useless.
When these cases are promptly taken in hand and judi-cipusly treated, arrest of the disease is possible; but in the great majority of instances the hopeful period is allowed to pass by before anything is done, when it runs its course unchecked. Once fairly established, the prospects of recovery are very remote, and in the most favourable circumstances success can only be looked for after months of treatment and an outlay often exceeding the value of the patient. Where treatment is determined upon, a dose of physic should be given at the outset, followed by a restricted diet. The diseased foot should then be thoroughly cleansed and disinfected by long immersion in a pail of antiseptic solution, the active principle of which may be carbolic acid, perchloride of mercury, or chloride of zinc. This done, all loose horny shreds should be removed, as well as horn underrun by the disease. Where fungous growth is exuberant it should be removed, either by the hot iron lightly applied or by some caustic agent, such as strong solution of chloride of zinc, powdered perchloride of mercury, sulphuric acid, or nitrate of silver. On the top of the caustic application a thick pad of tow should be placed so as to impart pressure to the diseased surface, and when bound on to the foot the whole may be transferred to a suitable "boot", and the dressing renewed at intervals of two or three days for so long as may be necessary. These, however, are not cases in which amateur doctoring is likely to succeed.
Fig. 398. - Canker.
Fig. 399. - Canker.
They require the services of the most enlightened and painstaking practitioner, who will recognize the changes for good or ill as they occur, and will regulate his treatment accordingly.