Report / Committee on Cattle Diseases.

  • Great Britain. Committee on Cattle Diseases.
Date:
1934
Catalogue details

Licence: Public Domain Mark

Credit: Report / Committee on Cattle Diseases. Source: Wellcome Collection.

    19/166 (page 17)
    30. In some infected animals the progress of the disease is arrested before it assumes a generalised form. We have received evidence that of animals slaughtered at Edinburgh and found to be tuberculous, about 10 per cent. have to be condemned entirely, about 20 per cent. have to be condemned in part, and the remainder or 70 per cent. are so slightly infected that the whole carcase may be sold. This 70 per cent., in fact, consists of two groups. In the first are those in which the disease is of such recent origin that it has not had time to spread. The second is that in which the disease is not generalised, having been brought under control by the animal’s natural powers of resistance. These cows are not free from the danger of a breakdown of their resistance against the disease in circumstances of exceptional strain. 31. Cattle, as has already been mentioned, may be shown to be infected with tuberculosis during life by their reaction to the introduction of tuberculin into their system. This test, however, generally fails to reveal infection incurred less than three or four weeks before the time of testing and sometimes infection incurred as much as three months previously. Unfortunately, reaction to the test does not show what is the stage of the infection, or whether the disease is progressive or quiescent. 32. Cattle become infected with tuberculosis either by inhaling or by ingesting infected material. The source of infection is normally another cow, though the disease may be contracted by contact with other infected animals, for example, with pigs. Indeed, to-day the disease may be contracted from a man suffering from bovine tuberculosis.* Unfortunately cattle, even at an early stage of the disease, excrete tubercle bacilli in great numbers. The principal sources of infected material are the lungs. Infected sputum, however, is swallowed, and in this way the feces become infected. The udder may eventually become infected, and the cow will in that case yield infected milk. But only a small proportion of tuberculous cows give infected milk. Generally speaking, tuber- culosis does not appear in the udder until the disease has reached an advanced stage. Thus infection may derive from matter passed through any of the principal channels of the body. The tubercle bacillus may, in favourable circumstances, remain alive for a con- siderable time after it has been excreted. The danger of infection through the use of premises is therefore very real, and there is also risk from the use of infected pastures. The incidence of tuberculosis is normally low in calves and heifers, but rises rapidly after the second year. Calves born from infected mothers are nearly always free from the disease and are likely to remain free if segregated at once and kept strictly isolated. - 88. No cure for tuberculosis 1s known, and once a herd is heavily infected it is likely to remain in that condition unless special * Namely, ulcerative, pulmonary, or renal tuberculosis of bovine origin.