26 



The milk of reacting cows may be used if it is first boiled or heated to a 

 point sufficient to kill the germs. This heating to a point less than boiling it is 

 called Pasteurizing, and is safe provided all the milk reaches the required degree 

 of heat and is kept there sufficiently long. For this it is necessary to keep the 

 milk for twenty minutes at 149 degrees Fahrenheit or for five minutes at 176 

 <legrees Fahrenheit. 



This system of dealing with tuberculosis in a herd was planned by Pro 

 fessor Bang, of Denmark, and has been very successfully followed in tliai 

 country for some years. It has the advantage of allowino' the reactors to hv 

 made use of while a sound herd is being built up. Under this system the sound 

 herd increases in numbers as healthy calves are added to it, while the diseased 

 lierd becomes pmaller as the reactors die off or are killed as open cases of tuber- 

 culosis. Finally a point is reached where only a few reactors remain and the 

 owner will then find it to his interest to kill them rather than have the trouble 

 of keeping them isolated. 



Some time is required for the successful carrying out of the Bang system, 

 and the owner must be prepared to follow it steadily and faithfully for the 

 whole time that is needed, which may be several years. During this time, . 

 the healthy herd must be tested every six months and any reactors removed 

 to the diseased herd. At the same time, a sharp lookout must be kept for 

 animals showing definite symptoms of the disease. These should be destroyed 

 ]>romptly as they are the irost dangerous source of infection. 



DEALING WITH A BADLY INFECTED HERD. 



Where the test shows more than half the number diseased a somewhat 

 different plan is required than the Bang system. This herd is so badly affected 

 that the non-reactors cannot safely be considered healthy. Many of them are 

 sure to have been infected with the disease quite recently, so that the test fails 

 to detect it. These will react at the next test and in the meantime may develop 

 tiie disease so rapidly as to infect others. This will repeat the difficulty occur- 

 ring at the first test, and it would be a long and tedious process of weeding 

 before even a small but perfectly healthy herd could be established. 



For these reasons it is better to treat such a herd as. if it Avere entirely 

 diseased, and to begin with the new-born calves to build up a healthy herd. 

 The method from this point is exactly the same as tbe Bang system,' except 

 that as there are no healthy cows to act as foster mothers, the calves must be 

 raised on pasteurized milk. At six months old, the calves are tested and reactors 

 are transferred to the other herd. This plan was devised by a German veter- 

 inary surgeon named Ostertag, and is known as the Ostertag system. It is very 

 successful when carefully carried out. 



AVhile getting rid of the disease by whatever system may be adopted, an 

 animal should never be bought for the healthy herd unless known to be healthy. 

 The tuberculin test should be applied, and if possible the animal should be 

 selected from a herd that is known to be free from tuberculosis, l^ew pur- 



