A corn is a bruise to the sole of the foot occurring at the inner heel, in the angle between the crust and its inflection - the "bar". The almost invariable occurrence of the injury at this point would seem to be due in part to the inner quarter being weaker and more yielding than the outer one, and in part also to its being more immediately under the centre of gravity.
The fore-feet are almost invariably its seat, and of these one or both may be affected.
The chief predisposing conditions to corn are the conformation and structure of the feet, and indifferent shoeing. With regard to the former, it may be remarked that flat feet with low, weak heels, and thin soles and crust are those most likely to contract the disease. Feet of a strong, upright, and blocky type, although less frequently affected, are, nevertheless, liable to attack. As to shoeing, excessive paring of the sole, removal of the bars, and undue lowering of the heels, all tend to weaken the part and expose it to injury. Shoes, when made too short and narrow at the heels, if insecurely nailed to the foot, or worn too long, are liable to displacement, and by becoming embedded within the crust occasion a bruise to the sole.
After one or two attacks of corn, predisposition to the malady is very much increased, and some horses are seldom entirely free from it. These chronic cases are chiefly due to a diseased and asperous condition of the heels of the coffin-bone, resulting from former attacks, which irritate or injure the sensitive structures on which they rest.
The actual existence of a corn is only made known after a portion of horn has been removed from the sole, in the angle between the bar and the crust, when a red spot varying in size from a pea to a sixpence will be found. The quantity of horn necessary to be taken away will depend on the time the corn has been in existence, i.e. whether it is an old corn or a recent one. In the former case the discoloration will be near the surface, and readily exposed and quickly "pared out". In the latter it will be deep down, near to the sensitive foot, and a considerable amount of horn may require to be removed before it is brought into view. The farther a corn is away from the surface the more recent it is, and the more likely it is to be a cause of lameness. Sometimes in paring a corn a quantity of dark-looking fluid escapes from between the horny and sensitive sole; it is then said to be a "suppurating" corn. Other symptoms of the disease are heat, especially over the inner quarter, tenderness to pressure, and lameness.
During progression the animal's step is short, and the foot is brought to the ground with the bearing specially on the outer side. In severe examples of suppurating corn the leg sometimes becomes swollen as high as the fetlock, or even the knee, and evinces considerable pain to pressure. In such cases the lameness is frequently referred to the leg, while the corn is altogether overlooked, until attention is directed to the formation of an abscess at the coronet, through which the matter in the foot escapes. This condition is known as a quittor.
A mild dose of physic is a good preliminary to the local treatment of corn. The foot will require to be carefully pared over the seat of injury, and should it be found to contain "matter", free vent must be given to it. The foot should then be put into a pail of warm carbolized water for half an hour, and afterwards transferred to a hot poultice of linseed-meal and bran. Before the poultice is applied, the corn should be dressed with a solution of carbolic acid, and covered over with a pledget of cotton-wool, so that none of the bran and meal may enter the wound. When the inflammatory action has been subdued, poulticing may cease, and the carbolized dressing may be applied three times a day, with the cotton-wool covering made secure by tapes or cross-sticks, and the foot enclosed in a bag or boot. Later, a blister over the coronet and cold water swabs to the feet, conjoined with rest, will complete the cure.
In mild cases of the disease cold-water irrigation, wet swabs to the feet, and rest on a soft surface are all that is required.
Leather soles and "stopping" should be worn for some time after the lameness has disappeared, and by some animals at all times.