T.B. AMONG PIGS

Hawke's Bay Tribune, Volume XXV, Issue 78, 15 March 1935, Page 13

T.B. AMONG PIGS

Milk As Infection Source RELATION TO DAIRYING It. is a well-known fact that the inci- j deuce of tuberculosis among pigs de- I pends largely on the extent of that disease among the dairy cattle with which the pigs are associated. This has been demonstrated in many ways, notably in Victoria, where an investigation carried out some y ears ago showed that the percentage of pig carcases found to be infected with tuberculosis at slaughter was very much higher in districts not subject to Government dairy supervision than was the case in districts where Government supervisors were actively engaged eliminating dairy cows affected with that ditcase. While this association between the degrees ot infection in the two classes of animals is generally recognised, says an Australian writer, there is not the same general appreciation of the methods by which the disease is spread from the cow to the pig. The common belief is that the organisms causing tuberculosis in the cow find their way into the milk and that when this milk is led to the pigs (either as skim or whole milk) the bacilli are taken in by that animal. Undoubtedly this method of infection is responsible lor some cases of tuberculosis among pigs, but, fortunately, it is not by any means a common method. Indeed it would be a very serious thing lor the community if tuberculosis were to readily spread. As a matter of fact, while the percentage ol tuberculosis among dairy cows is fairly high, it is only on rare occosions that the lesions caused by this disease occur in the ud--1 dvr or in any other part of the animal ' with which the milk comes in contact, i Tuberculosis of the udder is a disease ■ readily diagnosed, and one for which I the dairy supervisors and dairy farmers ) are always on the lookout. Immediate ' ly there is any suspicion that a cow is affected in that way she is withdrawn from production, her milk is discarded, ana, if subsequent veterinary examination confirms the early fears, she is destroyed. NO GREAT RISK. It is because of this constant watch ! for tuberculosis of the udder that the i milk supply generally is so free from i this disease. It follows, then, that the risk of infecting pigs with tuberculosis i organisms in milk is no greater than I the risk of infecting human beings from I that same source. Investigations carried out have shown beyond doubt that I under ordinary conditions of pig rais- | ing tuberculosis infection from milk is j of minor importance compared to the : degree of infection caused by the in- | gestion or swallowing of materials that j have been contaminated by the dung ol dairy cows suffering from tuberculosis in some portion of the body other than the udder. It has been shown also i that before the disease becomes established in the pig, repeated ingestion of the infective material is necessary. The natural body resistance to disease is sufficient to counter an occasional infection with comparatively tew organisms; indeed it has been established I that intermittent infection with a small j quantity of infective material may acti ually increase the animal’s resistance ! to the disease, a principle that is availI cd of in the use of vaccines. Where tuberculous cows exist there would be no shortage of infective material. As already pointed out, it. i>in comparatively lew cases only that the organisms find their way into the milk. In the case of an animal suffering with pulmonary tuberculosis, infective sputum will be coughed up by the animal, mixed with the cud in the mouth, and swallowed again. In this way the organisms reach the intestines, and eventually are excreted in the dung. Again, it has been found that the bile ot infected animals may contain tuberi cule bacilli which have been derived from disease lesions in the liver. These organisms ateo find their way out through the bowels. A third source from which the dung may become conI taminated with these organisms is provided by intestinal and peritoneal : lesions. ' While the number of cattle infected with tuberculosis of the udde r forms a very small percentage of the whole, those having lesions in the lungs, lymphatic glands, pleura, peritoneum or liver constitute the vast majority of affected cows, and it may be I readily realised that these cows form a I much greater menace to other animals on the farm than does the milk used for feeding purposes. This aspect of the problem of tuberculosis in pigs has been the subject of recent investigation in Queensland, where some interesting facts have been revealed. In the first place, it has been shown that when large numbers of pigs from any particular property are condemned because of tuberculosis, investigation invariably that the young pigs have been allowed free access "to areas soiled by the droppings of dairy cattle. POLLUTED GRAZING. One ciuse investigated was that of a I dairy farmer who for some year* had j suffered heavy losses from pig con--1 demnations. Believing that the pigs , were becoming infected through the milk, he decided to Iced no milk to his pigs unless it had first been thoroughly boiled. Hus, however, resulted in no decrease in the number of carcases condemned so it became apparent that there existed a definite source of infection apart from the milk A survey of the herd was made, and all cattle suspected of being infected wcie destroyed. Methods were adopted to ensure that the young pigs wore not allowed access to areas on which cattle | bad been run, and, although milk was i fed without prior boiling, not one carcase was condemned. Naturally, this > farmer has held to the practice of en- ! suring that liis pigs are kept entirely j separate from his dairy cow*. NumerI ous other cases are quoted by the Queensland authorities, all demonstrating that the dung of infected cattle is the most fruitful source of infection of pigs with tuberculosis. That tliis should bo so bocamos readi ily apparent when one considers the feeding methods of the young pig. It is a common thing for such an animal to nose under dried clumps of manure, seeking the small green shoots of grass usually to be found there. The presence ot moisture and warmth, and th* j absence of light afforded by the dung,

provide ideal conditions for the organisms, so that they are able to maintain their virulence for some time, and as the pig ingests the material under the clump ho takes in also a considerable number of these organisms. It has been noticed also that when cattle are fed on whole grain a proportion of this is passed out unchanged, and forms a great attraction to the pigs. In picking this grain out from the manure the pig is particularly likely to become infected with the organisms that would have passed through the bowel of a cow with tubercular lesions in any portion of the body from which they could reach the intestines. The foregoing facts suggest the steps that should be taken to eliminate tuberculosis from pigs. In the first place, any cows showing symptoms of tuberculosis, or which react to the überctilin test, should be eliminated from the herd. Secondly, the pigs should run in separate paddocks and at no time should they have access to areas that may have been contaminated by the droppings of the cattle.