30 



farmers' BULLETIN 834. 



fore, if cholera should appear on the premises such pigs should be 

 treated in the same way as the remainder of the herd. 



The opinion that pigs weighing less than GO to 75 pounds can not 

 be immunized successfully by the simultaneous method has become 

 more or less current in some sections of the country. The best avail- 

 able information indicates that this is not true. If ample serum is 

 administered with the virus these small shoats can be treated by the 

 simultaneous inoculation with safety, and certainly the great ma- 

 jority of them will derive a lasting immunity from the treatment. 



In testing hog-cholera serum to determine its potency it is common 

 to use pigs of this weight, and the test is made by giving them a 

 simultaneous inoculation of serum and virus. If the serum is good 

 these pigs remain in good health, and they are commonly given, when 

 they have attained a weight of 150 pounds or more, large doses of 

 virus to render them hyperimmune, for the production of serum. At 

 this time, as a rule, they are found to be firmly immune as a result 

 of the original simultaneous inoculation. 



RESTOCKING AFTER AN OUTBREAK OF HOG CHOLERA. 



In some instances the infection of hog cholera disappears within 

 a few weeks, while in other cases it remains for months. The in- 

 fection is more likely to be eliminated quickly in summer than in 

 winter. This is probably due to putrefaction and fermentation of 

 infected material, as experiments have shown that the virus of hog 

 cholera is usually destroyed by those processes. In the cold months 

 of winter, putrefaction and fermentation do not take place, and in- 

 fection persists for a longer time. No statement can yet be made of 

 the exact time required for the elimination of infection on farms. 



Sick hogs are a constant menace to nonimmune hogs, therefore 

 susceptible hogs should not be placed on a farm so long as any sick 

 hogs remain' on the premises. Nonimmune hogs should not be 

 brought on the farm where infection has existed until the premises 

 have been cleaned up by destroying old troughs, rubbish, litter, and 

 other material which may be contaminated. As a general rule the 

 introduction of susceptible hogs on previously infected farms can 

 not be regarded as safe at any season within less than 3 months 

 after the last sick hogs have been removed. Therefore it seems ad- 

 visable to immunize all new stock, including new litters, introduced 

 on the farm within 90 days after all hogs have recovered. 



TONIC COMPOUND. 



There are many so-called "tonics" advertised to do wonders for 

 hogs, and some of them may have merits as condition powders. 

 None, however, is of any value as a cure or preventive for hog 



