HANDLING HOG CHOLEEA IN THE FIELD 171 



that of using simultaneous treatment so that the 

 sow will be farrowing or nursing a newborn lit- 

 ter at a time when the resulting reaction is in 

 progress. 



The pigs likewise should be maintained on doses 

 of serum alone at four-week intervals until they 

 are at least nine weeks old, preferably twelve, and 

 then they should receive simultaneous treatment. 

 If they are fairly well isolated from the infected 

 animals the first dose of serum alone may be de- 

 layed until they are two or three weeks of age, 

 otherwise it should be given when they are only 

 a few days old. 1 



a The question whether young pigs acquire a permanent immu- 

 nity as a result of simultaneous treatment is yet unanswered. 

 Niles describes experiments indicating that they do, while Cahill 

 on the other hand found that over 50 per cent of several hundred 

 pigs given serum and virus between the ages of two and eight 

 weeks failed to acquire a permanent immunity as a result. Peter- 

 sen found that only fifteen out of one thousand ' ' baby pigs ' ' 

 given simultaneous treatment proved susceptible as old hogs. We 

 have collected very little experimental data on this point, the 

 results agreeing substantially with those of Niles. 



Our field observations, however, lead us to believe that a per- 

 manent immunity is not always established when serum and virus 

 are given to sucking pigs. In one instance we gave simultaneous 

 treatment to fifty pigs that were about eight weeks old. When 

 the animals had reached a weight of about 150 pounds, one of 

 them was brought to us for autopsy and showed undoubted lesions 

 of hog cholera. Three or four of the others developed symptoms 

 of the disease during the following week, so the entire herd was 

 revaccinated. Two of those that sickened died later but we did 

 not have an opportunity to perform autopsies. There is little 

 doubt that they died of hog cholera, but just how many more 

 would have died in the absence of a second injection is a matter 

 of conjecture. In another instance that came under our observa- 

 tion about eighty young pigs were given simultaneous treatment, 

 and when these animals reached a weight of about 180 pounds 

 each, approximately twenty of them died. We performed autop- 

 sies on several, and found unmistakable hog cholera lesions. 



