26 



Farmers* bulletin 834. 



that susceptible hogs may be kept within a few feet of cholera hogs 

 without becoming infected if care is taken to prevent the infection 

 being carried from the sick to the healthy animals. On the other 

 hand it has been noticed in practice that at times herds on farms 

 immediately adjoining outbreaks of cholera may escape the dis- 

 ease, while farms several miles away become infected. It is probable 

 that the ways in which cholera spreads are not yet fully understood, 

 but it is known that there are certain channels through which it fre- 

 quently is carried from farm to farm. These have been discussed in 

 the section headed " Modes of Infection." 



Notwithstanding the fact that at times herds on farms adjoining 

 an outbreak of cholera may escape the disease, it seems to be good 

 practice for farmers to protect their herds by inoculation when 

 cholera exists in the immediate neighborhood. This is particularly 

 true where the infected herd is not kept under strict quarantine 

 and where the quarters of the sick pigs are not continually cleaned 

 and disinfected. The serum-alone treatment may prove sufficient for 

 protecting healthy herds under such circumstanceSj particularly if 

 the disease on the neighboring infected farm is stamped out in a 

 short time and the premises are cleaned and disinfected properly. 

 As a general proposition, however, it would appear to be better to 

 use the simultaneous inoculation for protecting healthy herds, pro- 

 vided this treatment can be given by a competent veterinarian or by 

 a layman who is well trained and thoroughly familiar with the work. 

 After immunizing healthy herds in this way they should be handled 

 in very much the same way as an infected herd after treatment; 

 that is, the feed should be light, not much grain should be fed, and 

 the hogs should be kept in a clean, disinfected yard where they can 

 be watched carefully from day to day. In case the disease appears 

 in a herd after treatment, it should be re-treated promptly with 

 serum alone. 



Diseased herds. — In the field experiments conducted by the Bureau 

 of Animal Industry in 17 different counties during 1913, 1914, and 

 1915, it was the practice in some of the counties to use the serum- 

 alone treatment exclusively. In the remainder of the counties all of 

 the apparently healthy hogs in diseased herds received the simul- 

 taneous inoculation, while the sick hogs, including all those showing 

 temperatures above 104° F., received the serum alone. So far as the 

 results of treatment are concerned, the losses from cholera were 

 practically the same in the two sets of counties. However, in those 

 counties where serum alone was used on all hogs, whether sick or not, 

 in diseased herds, there was more or less recurrence of disease among 

 the treated hogs. In other words, the healthy hogs in the diseased 

 herds were protected for some weeks but later lost this immunity, 

 and the infection being still on the farm they then contracted cholera. 



