Other Diseases of Sheep

HADLEIGH MARSH AND E. A. TUNNICLIFF.

FOOT ROT sometimes is thought of as including several conditions of the feet of sheep, but we use the term firmly for only one specific infectious disease.

Its main symptom is severe lameness in one or more feet. A sheep whose fore feet are affected often feeds on its knees. Only the hoof is involved. No swelling or other change occurs in the foot or leg above the hoof.

The condition starts with a small sore on the inside of the claws or in the soft tissue of the bulb of the heel. From there it spreads under the born of the sole and inside the horny wall of the hoof. The dirty-gray, cheesy material formed between the horny wall of the hoof and the softer tissue beneath causes the horn to separate from the tissue beneath. The loosened horn becomes overgrown and the foot deformed. The diseased tissue stinks.

Foot rot develops and spreads among sheep when they are on wet ground, like swampy pastures and wet corrals. But pasturing on wet or muddy ground will not of itself produce foot rot. The infection must be brought in on the feet of a sheep that has foot rot. Then, if the ground is wet and the feet are softened, the infection may spread quickly through a flock. The disease does not spread when the sheep are on dry, hard range.

The infection lives only a short time in the soil. One need not be afraid of pastures or corrals where foot-rot sheep have been if the premises have had no sheep on them for a month although the infection actually dies out in less than a month.

Foot rot may be confused with festering conditions of the foot that are caused by infection with ordinary pus-producing organisms. The hoof itself in such cases is not primarily involved, but abscesses form in the tissues above the hoof. Sore feet may also occur in connection with contagious ecthyma (sore mouth) and lip-and-leg ulceration, but those lesions also are above the hoof itself.

The treatment of foot rot should start immediately after the diagnosis. The way to avoid a long and expensive experience with a diseased band of sheep is to tackle the condition vigorously with the aim of stamping out the infection as quickly as possible.

It is no good to spot the visibly lame sheep and treat them with something to make them feel better. Every sheep lame or not should be set up and every foot examined.

All feet that show anything wrong must be thoroughly trimmed to expose all diseased tissue. Enough of the horn must be cut away to expose every spot of infection, even if it is necessary to remove nearly all the horn. The sheep are then walked through a foot bath containing a saturated (30 percent) solution of copper sulfate. The unaffected sheep must also be walked through the foot bath. After treatment, the sheep should be moved to fresh dry pasture or range.

The feet will be cured if the trimming has been thorough. It seldom happens in actual practice that every foot is cleaned up on the first round. The sheep must be carefully examined at short intervals, and the process should be repeated until no infected feet can be found.

PROGRESSIVE PNEUMONIA is a slowly developing, chronic, progressive disease of the lungs. It is marked by a gradually increasing difficulty in breathing and emaciation.

Sheep affected with this disease are commonly known as "lungers" or "heavers" in the Northwestern States. Progressive pneumonia in the United States is a disease of range sheep. It has not been reported as occurring in the farm flocks of the Central and Eastern States.

The percentage of cases in infected flocks is difficult to estimate, but probably 2 to 3 percent a year is a reasonable figure. None of the affected sheep recovers.

It is less apparent in the young sheep than in older animals. Some of the ewes culled for age are actually lungers and are sold out of the range bands before progressive pneumonia kills them. Most of the sheep in which symptoms are observed are relatively old ewes-4, 5, and 6 years old. Clinical cases occur in younger sheep, but symptoms rarely appear in yearlings.

The main symptom is the gradually increasing difficulty in breathing. The rate of breathing, particularly after exertion, increases slightly at first.

As the condition advances, the affected ewes may be easily picked out after a drive, because their heads rise and fall with each breath. There is a double expiratory effort, which can be observed even in the early stages when the sheep are standing quietly after being moved. Over a period of several months the respiratory distress increases, and the sheep become emaciated and die. Lunger sheep live 2 or 3 months or even a year or more after symptoms are first noticed.

The pathological lesions are confined to the lungs. When the chest of a sheep dead of lunger disease is opened, the lungs do not collapse. They retain the shape of the chest cavity; when they are removed, they are three times as heavy as a normal lung. Instead of the normal bright-pink color, they have a combination of a dull-gray and dull, pale-red appearance. The tissues are so thickened that there is little airspace.

The cause of progressive pneumonia has not been determined. It is transmissible. The infective agent may be a virus.

No method of treatment has been developed. The slow development, the difficulty in recognizing the first stages, and the uncertainty as to the cause make treatment difficult.

The only method of control we can recommend is the elimination of affected sheep from a flock as soon as they are detected. Those that are detected early enough may have some slaughter value. A lunger will never raise a lamb. Any feed she consumes is wasted. The general practice of culling range ewes for age helps to eliminate lungers, because the disease is recognized oftener in old sheep than in the younger ones.

BLACKLEG is thought of generally as a disease that affects only cattle, but the fact is that it also causes serious losses among sheep.

Almost always it is possible to trace the source of the infection in sheep to a wound, which may be the result of shearing, dogbites, fighting among rams, difficult lambing in ewes, or docking of lambs. Where blackleg has developed in freshly sheared sheep or after docking, it usually is found that cattle have died of blackleg in the area and that the carcasses have not been burned.

The symptoms and lesions of blackleg in sheep are like those in cattle.

The treatment and prevention are the same as for cattle. The vaccine that is used for cattle can be used for sheep. When the dosage of vaccine for cattle is 5 milliliters, a dose of 3 ml. is enough to immunize a sheep. Because blackleg in sheep is somewhat sporadic, it has not become routine procedure to vaccinate. When blackleg losses occur following shearing, for instance indicating that the shearing plant and corrals are infective the flock should be vaccinated. Each year thereafter the young sheep should be vaccinated before exposure to the infected premises.

MASTITIS, also called mammitis, gar-get, or blue-bag, is an inflammation of the udder. Losses from mastitis in the western range States generally are considered to be of economic importance, for often it occurs in 4 percent of the ewes.

Without treatment, about 20 percent of the affected ewes die. One side of the udder of ewes that survive is permanently spoiled. The loss of lambs from stunting and bumming also is heavy.

Some of the cases that occur soon after lambing are caused by infection with filth bacteria, such as those found in unsanitary lambing quarters.

The more common type of mastitis in sheep may appear at any time from lambing to the time when the lambs are 3 to 4 months old. Investigations at the Montana Veterinary Research Laboratory showed that this type is caused by infection with a specific organism, Pasteurella mastitidis. This mastitis occurs quite generally in the Western States. It has been identified in Montana, Wyoming, Utah, Texas, and Oklahoma.

A band of 1,900 ewes, shed-lambed in Montana in April 1948, developed four cases by June 1. They then were moved to hard, dry, clean range, where they remained until fall. The sanitary conditions were excellent during the three summer months but 23 cases were detected in the first 45 days and 27 cases in the second 45 days.

Infection may develop in an udder that looks normal, but it is more apt to attack the abnormal or injured tissue. Heavy lambs are rough with the ewes when they nurse; sometimes they raise the mothers off the ground. The gland may easily be bruised so that the pasteurella organism gets a chance to grow and set up an infection. Nodules or cysts of any size, consistency, or location in the udder are potentially dangerous, for some of them harbor the organism and eventually break down to produce mastitis. Even the udder that looks and feels normal may harbor the organism for an entire season without producing the disease, but this same udder may be a source of infection for other ewes.

Transmission of the infection would seem to take place by contact of the end of the teat with infection on the bed ground.

The first noticeable symptoms are loss of appetite and dejection. The ewe stands off by herself, drops behind while being moved or trailed, and does not allow her lamb to nurse. Forced to move, she shows lameness in one hind leg because of the painful udder. That is an important early symptom. She swings the hind leg of the affected side outward to avoid contact with the painful side of the udder. The first day the udder is painful and hot, without too much enlargement or discoloration, and the milk is normal.

Within 24 hours after the first symptoms are noticed, the glands enlarge and begin to harden. The secretion changes through the successive stages of whey separation, casein coagulation, and finally a caking of the udder in which there is no secretion. This process usually takes place in 4 to 6 days.

The udder may or may not become discolored. The bluish discoloration is responsible for the term "blue-bag" a misleading term, because the condition occurs in few cases. The infection is practically always on one side. The unaffected side and milk are normal unless the animal remains extremely ill for some time; then milk secretion ceases. The process terminates in a hard, enlarged udder, or abscessed udder. Either way, the ewe's economic reproductive life is ended. She should be marked for culling.