ENCREASED TRAFFIC IN (TUBERCULOUS) ANIMALS. DAIRY EXTENSION.
In common with all infectious diseases, tuberculosis owes its great extensions to the sale and purchase of animals. Where an indigenous race of cattle is raised and sold, without any additions from without, tuberculosis is usually rare and confined to the one herd, or to those having intimate intercommunication with it. Where, on the other hand, a large stock is kept up, as in milk dairies, and few or no calves are raised, but the bulk of the cows are sold off yearly and replaced by new purchases, tuberculosis, sooner or later, finds admittance through the body of an infected animal, and once implanted in the herd, it goes on encreasing, without limitation, except by the sale or death of the more seriously affected. The larger the herd and the greater the number of yearly changes, the greater the number of opportunities for the introduction of an infecting animal. Where a great part of the herd is turned off yearly, and the new animals are drawn from any or every source indiscriminately, it would border on the miraculous if such a herd were to remain free from the infection for any great length of time. The recent extension of tuberculosis in herds has been coincident with the great development of commerce in live stock, and the rapid transit on land and water by steam. Before the days of the steam engine, animal plagues advanced slowly and uncertainly, excepting in the presence of a great European war, which drew animals from all available sources, congregating them in large mutually infecting droves in commisariat parks, and marching them in the wake of the army for its daily supply. Inevitably every country invaded was infected, and the plagues spread from the line of march in all directions. The more deadly plagues, like rinderpest and lung plague, were the first to appear, and in this lay a certain measure of palliation of the evil, as the exposed and often weaker animals were killed off, so that the slower contagion like that of tuberculosis had not time to develop. This mitigating influence held good so long as the deadly plagues were not placed under effective control. When, however, a nation successfully extirpated and excluded lung plague and rinderpest, the way was opened for a freer extension of tardily developing plagues like tuberculosis. The great development of beet sugar factories and the accumulation of herds to consume the marc; the extraordinary extension of manufactures which have made England and certain countries of Western Europe consuming rather than agricultural lands, and the wonderful modern expansion of dairy husbandry have combined to encrease and concentrate the cattle industry in ratio with the manufacturing and commercial progress of the nations, and as the live stock are kept under a milk-stimulating regimen and a life passed largely indoors, the way has been open for an ever-advancing encrease of tuberculosis. In the United States the centralization of population in the Eastern States and in all great centres of industry and the concentration of cows for the milk supply, and in certain districts in connection with butter and cheese factories, have contributed to wide local extensions of consumption. Hence it has been no uncommon thing to find herds in the vicinity of cities with 20 to 100 per cent. affected, in striking contrast with the 0.02 per cent. found in the fat cattle from the plains.
The modern railway traffic brings to all these swarming centres of animal industry, live cattle from long distances to supply the constant depletion through deaths and the disposal of dry cows, and thus the whole Atlantic slope is drawn upon to fill the eastern stalls. Infected animals thus shipped from Ohio, Indiana, Illinois, Wisconsin and Michigan for the good of the herds in those states find new homes in New York, or New England, where they have four to twelve mouths to propagate the infection before they are themselves disposed of. As in the days of the lung plague in America, the eastward trend of bovine traffic, becomes to a certain extent a protection and benefit to the herds of the west, but in equal ratio it operates to the detriment of our eastern stock. What is true of the planting of new centres of infection in the busy dairy districts of the east, and of the steady increase of disease in already infected herds, through the constant addition of new cases purchased, is no less true of the corresponding districts devoted to dairying interests in the west. It is the natural order of things, that, everywhere, the new accessions of infection, coming in the lines of trade, into large dairy herds, kept to a great extent indoors for months at a time, must hasten the general infection of such herds. When, therefore, no intelligent measures are interposed to check the evil, we must expect that the marked increase in the prevalence of tuberculosis, which we have witnessed of late years, shall become more and more evident year by year. Journals have claimed credit for befriending the stockman, in opposing all control of the cattle traffic, dealers have denounced all control as ruinously oppressive and injurious, and legislators have turned a deaf ear to the warnings of science and experience, but time, in this as in all other plagues, will justify the demand for an intelligent control, and the increasing losses will one day open the eyes of the stockowners to the fact that their truest friends are those that would exclude the baneful seed, and kill it ere it has had time to germinate and bring forth its ever increasing harvests.
In the absence of any systematic and efficient government protection in this line, the stock owner can only protect his sound herd by the rigid exclusion of all animals that are not of his own breeding, or in case of purchase, by an exhaustive inquiry as to the occurrence of sickness or deaths in the herd from which he buys, and by the professional examination and test of every animal to be bought. Even then he must promptly separate, test, and, if necessary destroy any animal that proves unthrifty, or which by cough, diarrhœa, wheezing or other sign gives evidence of probable tuberculosis.
Unregulated Traffic in Tuberculous Animals from Other States. The danger of buying animals untested is in no degree lessened when they are sent in from other states. While some make a business of supplying the store market with what they believe to be good stock, there is always the temptation to turn off animals that are unthrifty or poor milkers and which have proved less profitable than the others. Some even have the herd tested and sell off those that show evidence of tuberculosis. Unless, therefore, it is held in check by the tuberculin test, the traffic is made to the extent of such sales a direct means of disseminating tuberculosis.