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.