FOR THE MAN ON THE LAND

Northern Advocate, 29 December 1934, Page 15

FOR THE MAN ON THE LAND

TUBERCULOSIS IN COWS SOURCES OF INFECTION. SEVERAL RELIABLE TESTS. (Prepared by Massey Agricultural College). Compared with all other countries in which dairying is. carried on extensively, this country is fortunate in having so low a percentage of the cattle population affected seriously with tuberculosis. In fact, it is unfortunate that such a disease is allowed to continue to exist when it is one of those diseases which can be efficiently controlled, if not completely eradicated. At the same time one cannot lose sight of the enormous losses which the presence of tuberculosis in our herd produces both directly and indirectly. Naturally enough, it is the direct loss which engages the farmer’s mind. He mourns the loss of a good producer or it may be a good breeder. That is a very obvious loss. But what about the losses which are going on unseen or not realised —loss of constitution and the trail of diseases which follow on in its wake; breeding troubles, digestive troubles, lung troubles and udder troubles. With udder troubles alone the loss to the dairying industry is such that one can only hazard a guess at its amount. Tuberculosis is not one of those obscure conditions like indigestion, which may arise from a great variety of causes. It has a definite cause—the bacillus of tuberculosis. It is produced by the entrance into the body of the animal, either by being taken into the tnouth’ or bowel with food, or taken

into the lungs by means of dust or into the skin through small injuries of this organism.

Fortunately, when outside the body, it does not increase in numbers like some bacteria. Inside the body it multiplies, forming in time definite areas of infection which are apparent to the naked eye. In fact, they may become so large that they may be seen as swellings on the surface of the animal body: and in the dairy cow it may show itself as a hardening of the udder. This does not rncan that all hard udders are tubercular; many arc, although they appeared to follow an attack of mammitis.

Animal Sources of Infection

Once the organism is established in the animal body the organism can be found in the discharges of all cavities and canals where the organism exists, e.g., in the dung from infected bowels, in phlegm from an infected lung, in the saliva, in the urine of an affected kidney, and the vaginal discharges of an affected uterus. They are in the milk of a cow with an affected udder. They are in the milk of a cow showing symptoms in the udder. They may be in the milk of a cow with an apparently healthy udder. They are not usually present in the milk of a cow whose only symptom is a reaction to the test for tuberculosis.

The milk of one cow in a herd will infect the milk of all by mixing or merely handling the milk in infected cowsheds.

All animals and birds may become naturally infected. Cattle and man are most frequently infected, and then follows the pig, cat, dog, horse, camel and goat. Contrary to popular belief,

natural infection only occurs after prolonged exposure and repeated actual infection. It is the degree of infection which determines the severity of the attack. This is a very important point to be used ns an aid in eradicating the disease.

Lesions is the name given to those parts of the body which are damaged by the invasion of the bacteria into the body. Although the bacteria may be carried to all parts of the body in the blood stream, they arc mostly found in the lymph glands in a form most readily seen by the naked eye. That is the reason why the inspector, in examining an animal which has been destroyed because of tuberculosis, always examines the lymph glands. The gland which are most frequently noted by the farmer are those in the region of the throat, the glands situated just above the point of the shoulder, those lying immediately above the flank, and those placed deep in at the attachment of the udder. Animals which show affected glands are called clinical cases to distinguish them from those which have tuberculosis but do not show any signs whatever. Of course it does not follow that because of tuberculosis in an animal which failed to pass the test that the test must be at fault. The test applied to establish the presence of tuberculosis merely indicates its presence or not; it gives no indicaion whatever as to the extent or degree of infection. Symptoms. Let it be clearly understood that the diagnosis of tuberculosis is no simple matter. The more one has to examine tuberculous or suspected tuberculous animals, the more reluctant will that individual become in expressing a definite opinion. The only definite and safe procedure is to apply a reliable test.

In keeping with the remarkable variation in the changes produced in the animal body as a result of this disease, the symptoms of tuberculosis not only vary in the different animals, i.e., cattle and pigs, but to an almost equal extent in animals of the same species, e.g. cattle. In cattle, where the infection lies mainly in the lungs, the animal usually emits a short, dry vigorous cough. This is not frequent at first, but only occurs through some unusual influence on the air passages, such as cold or dusty air. They will also cough if they are suddenly roused or take a cjrink of cold water. Nothing untoward will be noticed, for appetite will be good and so ■also the general appearance. If given a long drive the tuberculous animal Will be the first to fatigue although 'otherwise appearing healthy. This short cough will probably last for months, in fact it usually is present for some considerable time before any notice is taken of it. Gradually, however, other symptoms make their appearance and indicate more clearly that all is not well with the animal’s lungs. The cough becomes more frequent and it may even become painful; it is coarse at first and it. may become feeble and almost noiseless. On the animal coughing, it may be noticed swallowing immediately after. If it does, it is swallowing the discharge which it has coughed up. With the increase of coughing there is an increased number of respirations and further they are not so freely made as in the healthy animal. This change in the respiration and in its mode of action, is best seen after a little exercise. To try and diagnose the presence of tuberculosis by applying the car to the thorax is absolutely useless. Most extensive growths can be present and not the slightest indication be given that they are there. Tuberculosis of the throat is not uncommon. It is usually accompanied with Very noisy breathing. This type of breathing must not be confused with nasal catarrh, which also has a noisy breathing; in the latter condition, it should be quite apparent that the breathing sound is coming from the nose and not the throat. Further, these animals do quite a considerable amount of coughing whilst those with nasal catarrh do not.

In the abdominal cavity there may be quite extensive infection and yet nothing will be indicated by the

animal. Now and again, when the

i ovaries are involved, a sexual excitement takes place, resulting in some instances of “buffers.' When the udder becomes involved., it is not usual for it to be ushered in with a severe inflammation. To the farmer all that he may notice is a gradual hardening of one or more quarters and with that, a gradual change in the appearance of the milk. The volume of “milk" produced usually remains about normal. As the disease advances it diminishes in quantity whilst changes occur in the appearance of the secretion. It becomes a more oV less watery fluid with flakes and curdled masses floating in it. », General Symptoms, As a variety of organs or tissues are usually involved at the same time, it will be obvious that the appearances of any groups of affected animals will vary considerably. The picture shown by each will be controlled by the organs affected in each. Therefore, it is impossible to describe, unless in a very .complex and involved way, the clinical picture of tuberculosis. A feature which is more or less common to all advanced cases is unthriftiness. The animal becomes dull, listless, there is a steady but progressive loss of condition, the coat is harsh; the animal loses appetite, the eye is sunken but remarkably bright. The temperature is usually higher in the evening than in the morning. The bowel may be normal, but diarrhoea may be present. Coughing may be present, but it just as frequently is not. Many objections could be made to this description, because it by no means covers all the symptoms which are to be seen in every-day practice. Many an animal has been slaughtered, apparently' in the “pink” of condition, but in actual fact the whole carcase has been affected and all had to be condemned. It is fortunate that so important a disease as tuberculosis can be definitely diagonised by means of a material called Tuberculin. Altogether there are seven tests. All are equally reliable in expert hands. Tuberculin is a product of the bacillus of tuberculosis in a suitable solution. The seven tests which are used, all depend on the reaction of the body to the presence of tuberculin. If the body is free from tuberculosis the body will not re-act to the presence of the tuberculin but if tuberculosis is present then the body will re-act. The re-action which takes place depends upon the test which has been used. It will fall into one of three categories:— 1. A thermal re-action indicated by a rise in temperature. 2. A tumification or swelling of some part of the skin at the seat where the tuberculin was introduced. 3. A purulent discharge from the eye. There is a general impression that tuberculosis is a hereditary disease. This is not so. There is hereditary predisposition, but calves are not born with the disease except under special circumstances such as being born from a tuberculous uterus. In order to save the calves one must endeavour to avoid feeding them infected milk and contact with tubercular adults. Tuberculosis is one of the scheduled diseases in the Stock Act. All stockowners are bound by law to report all cases or suspected cases at once, to the local Government veterinary surgeon or stock inspector, which is nearest.