HOW TUBERCULOSIS SPREADS FROM A DISEASED HERD 
TO A HEALTHY ONE. 
r r , UBERCULOSIS may be introduced into a healthy herd by any 
of the following means: 
By the addition of an animal that is affected with the disease; 
therefore animals should be purchased only from herds known to be 
free from tuberculosis, or from herds under supervision for the eradi¬ 
cation of the disease. 
By feeding calves with milk or other dairy products from tubercu¬ 
lous cows; this frequently occurs where the owner purchases mixed 
skim milk from the creamery, and feeds it to his calves without first 
making it safe by boiling or pasteurization. 
By showing cattle at fairs and exhibitions; reports have indicated 
that numerous herds have become infected through mingling with 
infected cattle at shows or by occupying infected premises. 
The shipment of animals in cars which have recently carried dis¬ 
eased cattle and which have not been disinfected properly. 
Community pastures; pastures in which tuberculous cattle are 
allowed to graze are a source of danger. 
In most cases the outward appearance of the animal bears no rela¬ 
tion to the degree of infection. The disease frequently develops so 
slowly that in some cases it may be months or even longer before any 
symptoms are shown; therefore be on the safe side and have your 
herd tested. 
Contribution from the Bureau of Animal Industry 
JOHN R. MOHLER, Chief 
Washington, D. C. 
November, 1919 
