Side-bones are hard, unyielding formations situated immediately above the coronet towards the heel. Pathologically considered, they consist in a transformation of the lateral cartilages into bone by the deposition into their structure of calcareous salts. This change is sometimes preceded by inflammation of the tissue of the cartilage, but in a large percentage of cases no such antecedent state exists.
Before the days of the Shire Horse Society, a very large proportion of our heavy horses became victims of the disease, resulting in a diminution in their value from 25 to 75 per cent. Thanks to the rigid veterinary inspection instituted by this Society, and more or less completely adopted by others, the prevalence of the malady has been so far reduced as to encourage the hope of its becoming as rare as it was common.
Side-bone is one of the most pronounced of hereditary diseases. Its tendency to arise in the progeny of affected animals is now known to every horse-breeder of experience, and we owe it to the growing recognition of this fact, and the more judicious selection of breeding stock, that the existence of the disease has been so largely curtailed. In some families the hereditary disposition to side-bone is so strongly marked as to respond to the most feeble of exciting causes. These commonly take the form of blows to the coronet, concussion to the feet, sprain of the cartilages, too early and severe work, especially on deep strong land where short turnings and heavy pulls are required at the headlands. High-heeled shoes and high calks are also said to excite it, but these bear a small proportion, if any, to the other inducing causes.
The actual presence of side-bone is made known when the cartilage or a part of it has become hard and unyielding and lost its natural elasticity and spring. This change, with rare exceptions, commences deep down at the point where the cartilage is connected with the pedal or " coffin " bone. There is, therefore, a period in its early development when it may not be recognized with certainty owing to its enclosure within the hoof. In the course of time, however, it becomes obvious to the touch, and in many instances to the sight also, appearing as a rounded prominence on the coronet towards the heel. The disease may affect only one foot, or both, or one side of a foot, or both cartilages may be involved at the same time or consecutively. In some instances side-bones are of slow growth, while in others the whole of the cartilage undergoes rapid ossification. Lameness is by no means a necessary result of side-bone. Numerous cases occur without giving rise to any obvious change in the animal's action, while others are attended with considerable pain or even complete disablement. In the latter examples the foot is hot, the action short, and the tread wanting in firmness, with an inclination to the sound side of the foot, if such there be. When in the stable the animal stands with the heel slightly raised from the ground, and if both feet are affected the weight is shifted from one limb to the other at longer or shorter intervals.
In all cases of foot-lameness in heavy horses where no obvious cause for it exists, side-bone should be suspected and prompt treatment adopted. Where a pond is available the horse should be made to stand in it two or three hours a day for a week, and should be afterwards blistered over the coronet and pastern every fortnight for three times, or oftener if required. In the intervals he should be turned into a damp meadow or river-side pasture, or into a yard well littered with peat or tan. Should blistering fail to remove the lameness, firing must be next resorted to. In old cases firing should be adopted at once. Cutting fissures in the hoof by means of a saw, or dividing the nerves of the foot, are the last and heroic measures of side-bone treatment.