174 HOG CHOLEEA 



isolation only because repeated trials have proved 

 it effective. 



Establishing and maintaining a hog cholera 

 immune herd. So far we have dealt with hog 

 cholera after it has reached the herd. We are 

 now to consider methods of preventing it from in- 

 fecting the herd, which yield even better results. 

 In their relation to the prevention of hog cholera, 

 most herds fall into three general classes: those 

 from which the virus can be excluded ; those con- 

 stantly threatened with hog cholera; and pure- 

 bred herds from which immune breeding stock is 

 sold. The herds in the first class do not require 

 immunization; those in the other two classes are 

 best maintained immune. 



The first question to be decided when a client 

 consults his veterinarian is whether it is really 

 necessary for the herd to be maintained immune. 

 Is hog cholera prevalent in the vicinity? Has it 

 appeared periodically on the farm in question? 

 Is the herd subsisting partially or wholly on gar- 

 bage f Is the breeder buying in hogs at frequent 

 intervals? Does he take sows to neighboring 

 farms to be bred, or are sows brought to his farm 

 for the same purpose? Has he an established 

 market for immune breeding stock, or does he 

 wish to establish one? Has the herd access to a 

 stream that may be contaminated with hog chol- 

 era virus ? If all these questions can be answered 



