DISEASE IN PIGS

Taranaki Daily News, 23 March 1935, Page 24 (Supplement)

DISEASE IN PIGS

TUBERCULAR INFECTION RELATION TO DAIRY COWS. It is a well-known fact that the incidence of tuberculosis among pigs depends 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 years 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 disease. While this association between the degrees of 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 fed to the pigs (either as skim or whole milk) the bacilli are taken in by that animal. Undoubtedly this method of infection is responsible for some cases of tuberculosis among pigs, but, unfortunately, it is not by any means a common method. Indeed it would be a very serious thing for the community if tuberculosis were so readily spread. As a matter of fact, while the percentage of tuberculosis among dairy cows is fairly high, it is only on rare occasions that the lesions caused by this disease occur in the udder or in any other part of the animal with which the milk comes in contact. Tuberculosis of the udder is a disease readily diagnosed, and one for which the dairy supervisors and' dairy farmers are always on the lookout. Immediately there is any suspicion that a cow is affected in that way she is withdrawn from production, her milk is discarded and if subsequent veterinary examination confirms the early fears she is destroyed. NO GREAT RISK TO PIGS. It is because of this constant watch for tuberculosis of the udder that the milk supply generally is so free from this disease. It follows, then, that the risk of infecting pigs with tuberculosis organisms in milk is no greater than the risk of infecting human, beings from the same source. Investigations have shown beyond doubt that under ordinary conditions of pig raising tuberculosis infection from milk is of minor importance compared with the degree of infection caused by the ingestion or swallowing of materials contaminated by the dung of dairy cows suffering from tuberculosis in some portion of the body other than the udder. It has been shown also that before the disease becomes established in the pig repeated ingestion of the infective material is necessary. The natural resistance to disease is sufficient .to counter an occasional infection with comparatively few organisms; indeed it has been established that intermittent infection with a small quantity of infective material may actually increase the animal’s resistance to the disease, a principle that is availed of in the use of vaccines. Where tuberculous cows exist there would be no shortage of infective material. As already pointed out, it is in comparatively few cases only that the organisms find their way into the milk. In the case of an animal suffering from pulmonary tuberculosis infective sputum will be coughed up by the animal, will be 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 of infected animals may contain tubercule bacilli derived from disease lesions in the liver. These organisms also find their way out through the bowels. A third source from which the dung may become contaminated with the organisms is provided. •by intestinal and peritoneal lesions. While the number of cattle infected with tuberculosis of the udder 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 readily realised that these cows form a much greater menace to other animals on the farm than does the milk used for feeding purposes. , QUEENSLAND INVESTIGATIONS. Th 15 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 discloses that the young pigs have been allowed free access to areas soiled by the droppings of dairy cattle. One case investigated was that of a farmer who for some years had suffered heavy losses through his pigs being condemned. Believing that the pigs were becoming infected through the milk, he decided to feed no milk to them unless it had first been thoroughly boiled. That, 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 were destroyed. Methods were adopted to ensure that the young pigs were not allowed access to areas on which cattle had been run, and although milk' was fed -without first boiling not one carcase was condemned. Naturally, the farmer has held to the practice of ensuring that his pigs are kept entirely separate from his dairy cows. Numerous 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 this should be so becomes read-' 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 of moisture and warmth and the 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 he takes in also a considerable number of the 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 organisms that pass 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 that steps that should be taken to eliminate tuberculosis from pigs. In the first place, any cows showing symptoms of tuberculosis or reacting to the tuberculosis 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.