442 



Pork Production 



with a pure-bred sire produces pigs which are one-half 

 pure. When the gilts of this litter are mated with a pure- 

 bred sire, the result is a litter three-fourths pure in breed- 

 ing. The third top cross produces pigs seven-eighths 

 pure-bred, or very high grades and the next cross fifteen- 

 sixteenths pure. For feeding and market purposes, the 

 high-grade pig is practically the equal of the pure-bred. 



FIG. 



19. Showing rate of improvement in up-grading and degree of 

 improvement effected in each generation. 



For breeding purposes, however, the high grade, although 

 good in individuality, is unreliable and disappointing. 



As illustrated by the diagram, improvement in the up- 

 grading process is at first rapid and then more slow with 

 each succeeding generation. The degree of improvement 

 effected by the first cross with the pure-bred sire is twice 

 as great as that in the second generation ; and in the third 

 generation the degree of improvement is only one-half 

 that in the second. Improvement in succeeding genera- 

 tions becomes more and more imperceptible as the high- 



