The horny covering of the sheep’s foot extends up, gradually thinning out, some way between the toes and divisions of the hoof, and above these horny walls the cleft is lined with skin. When the points of the toes are spread apart, this skin is shown in front, covered with short, soft hair. The back part of the toes, or the heels, can be separated only to a little distance, and the skin in the cleft above them is naked. In a healthy foot, the skin throughout the whole cleft is as firm, dry, and uneroded as on any other part of the animal.
The first symptom of hoof-ail is a slight erosion, accompanied with inflammation and heat of the naked skin in the back parts of the clefts, immediately above the heels. The skin assumes a macerated appearance, and is kept moist by the presence of a sanious discharge from the ulcerated surface. As the inflammation extends, the friction of the parts causes pain, and the sheep limps. At this stage, the foot, externally, in a great majority of cases, exhibits not the least trace of disease, with the exception of a slight redness, and sometimes the appearance of a small sore at the upper edge of the cleft, when viewed from behind.
The ulceration of the surface rapidly extends. The thin upper edges of the inner walls of the hoof are disorganized, and an ulceration is established between the hoof and the fleshy sole. A purulent fetid matter is discharged from the cavity. The extent of the separation increases daily, and the ulcers also form sinuses deep into the fleshy sole. The bottom of the hoof disappears, eaten away by the acrid matter, and the outer walls, entirely separated from the flesh, hang only by their attachments at the coronet. The whole fleshy sole is now entirely disorganized, and the entire foot is a mass of black, putrid ulceration; or, as more commonly happens, the fly has struck it, and a dense mass of writhing maggots cover the surface, and burrow in every cavity.
The fore-feet are generally first attacked; and, most usually but one of them. The animal at first manifests but little constitutional disturbance, and eats as usual. By the time that any considerable disorganization of the structures has taken place in the first foot, and sometimes sooner, the other forefoot is attacked. That becoming as lame as the first, the miserable animal seeks its food on its knees; and, if forced to rise, its strange, hobbling gait betrays the intense agony occasioned by bringing its feet in contact with the ground. There is a bare spot under the brisket, of the size of a man’s hand, which looks red and inflamed. There is a degree of general fever, and the appetite is dull. The animal rapidly loses condition. The appearance of the maggot soon closes the scene. Where the rotten foot is brought in contact with the side, in lying down, the filthy, ulcerous matter adheres to, and saturates the short wool—it being but a month and a half, or two months, after shearing—and maggots are either carried there by the foot, or they are soon generated there. A black crust is speedily formed round the spot, which is the decomposition of the surrounding structures; and innumerable maggots are at work below, burrowing into the integuments and muscles, and eating up the wretched animal alive. The black, festering mass rapidly spreads, and the poor sufferer perishes, apparently in tortures the most excruciating.
Sometimes but one forefoot is attacked, and subsequently one or both hind ones. There is no uniformity in this particular; and it is a singular fact that, when two or even three of the feet are dreadfully diseased, the fourth may be entirely sound. So, also, one foot may be cured, while every other one is laboring under the malady. The highly offensive odor of the ulcerated feet is so peculiar that it is strictly characteristic of the disease, and would reveal its character, to one familiar with it, in the darkest night.
Hoof-ail is probably propagated in this country exclusively by inoculation—the contact of the matter of a diseased foot with the integuments lining the bifurcation of a healthy foot. That it is propagated in some of the ways classed under the ordinary designation of contagion, is certain. That it may be propagated by inoculation, has been established by experiment. The matter of diseased feet has been placed on the skin lining the cleft of a healthy foot under a variety of circumstances—sometimes when that skin is in its ordinary and natural state, sometimes after a very slight scorification, sometimes when macerated by moisture; and under each of these circumstances the disease has been communicated. The same inference may be drawn, also, from the manner in which the disease attacks flocks. The whole, or any considerable number, though sometimes rapidly, are never simultaneously attacked, as would be expected, among animals so gregarious, if the disease could be transmitted by simple contact, inhaling the breath, or other effluvium.
The matter of diseased feet is left on grass, straw, and other substances, and thus is brought in contact with the inner surfaces of healthy feet. Sheep, therefore, contract the disease from being driven over the pastures, yarded on the straw, etc., where diseased sheep have been, perhaps even days, before. The matter would probably continue to inoculate, until dried up by the air and heat, or washed away by the rains. The stiff, upright stems of closely mown grass, as on meadows, are almost as well calculated to receive the matter of diseased feet, and deposit it in the clefts of healthy ones, as any means which could be artificially devised. It is not entirely safe to drive healthy sheep over roads, and especially into washing-yards, or sheep-houses, where diseased sheep have been, until rain has fallen, or sufficient time has elapsed for the matter to dry up. On the moist bottom of a washing-yard, and particularly in houses or sheds, kept from sun and wind and rain, this matter might be preserved for some time in a condition to inoculate.
When the disease has been well kept under during the first season of its attack, but not entirely eradicated, it will almost or entirely disappear as cold weather approaches, and it does not manifest itself until the warm weather of the succeeding summer. It then assumes a mitigated form; the sheep are not rapidly and simultaneously attacked; there seems to be less inflammatory action constitutionally, and in the diseased parts; the course of the disease is less malignant and more tardy, and it more readily yields to treatment. If well kept under the second summer, it is still milder the third. A sheep will occasionally be seen to limp; but its condition will scarcely be affected, and dangerous symptoms will rarely supervene. One or two applications made during the summer, in a manner presently to be described, will suffice to keep the disease under. At this point, a little vigor in the treatment will rapidly extinguish the disease.
Treatment. The preparation of the foot, where any separate individual treatment is resolved upon, is always necessary, at least in bad cases. Sheep should be yarded for the operation immediately after a rain, if practicable, as the hoofs can then be readily cut. In a dry time, and after a night which left no dew upon the grass, their hoofs are almost as tough as horn. They must be driven through no mud, or soft dung, on their way to the yard, which would double the labor of cleaning their feet. The yard should be small, so that they can be easily caught, and it must be kept well littered down, to prevent their filling their feet with their own excrement. If the straw is wetted, their hoofs will not, of course, dry and harden as rapidly as in dry straw. If the yard could be built over a shallow, gravelly-bottomed brook, it would be an admirable arrangement; for this purpose, a portion of any little brook might be prepared, by planking the bottom, and widening it, if desirable. By such means the hoofs would be kept so soft that the greatest and most unpleasant part of the labor, as ordinarily performed, would be in a great measure saved, and they would be kept free from that dung which, by any other arrangement, will, more or less, get into their clefts.
The principal operator seats himself on a chair, having within his reach a couple of good knives, a whetstone, the powerful toe-nippers already described, a bucket of water with a couple of linen rags in it, together with such medicines as may be deemed necessary. The assistant catches a sheep and lays it partly on its back and rump, between the legs of the foreman, the head coming up about to his middle. The assistant then kneels on some straw, or seats himself on a low stool at the hinder extremity of the sheep. If the hoofs are long, and especially if they are dry and tough, the assistant presents each foot to the operator who shortens the hoof with the toe-nippers. If there is any filth between the toes, each man takes his rag from the bucket of water, and draws it between the toes, and rinses it, until the filth is removed. Each then takes a knife, and the process of paring away the horn commences, upon the effectual performance of which all else depends. A glance at the foot will show whether it is the seat of the diseased action. The least experience cannot fail in properly settling this question. An experienced finger, even, placed upon the back of the pastern close above the heel, will at once detect the local inflammation, in the dark, by its heat.