CHAPTER XXXII 

 HYBRIDIZATION IN ANIMAL BREEDING 



Within the past century the tendency in practical breeding operations 

 has been toward the upbuilding of different breeds by a process of rigid 

 selection. Naturally this method of breeding has looked upon any 

 suggestion for the introduction of foreign blood with intolerance, an 

 intolerance which is shown particularly in the rigid requirements of 

 registration laid down by all breeders' associations. But the work in 

 plant breeding in particular has demonstrated that occasionally hybrids 

 have a commercial value in themselves aside from their usefulness as a 

 source for the establishment of new varieties. Accordingly within the 

 past decade there has been a growing tendency to investigate more 

 closely the question of hybridization in animals, both in its scientific and 

 practical aspects. 



Grading. In practical animal breeding grading refers to the method of 

 improving a herd of animals of indifferent blood by the use of pure-bred 

 sires. In the United States this practice has been very common on western 

 ranches where the common scrub stock of the range has been graded up 

 largely by the use of Hereford bulls, and bulls of other beef breeds. The 

 practice is very common in horse breeding throughout the entire nation, 

 for a large proportion of the stallions which stand for public service are 

 pure-bred animals. In horse-breeding, however, it is regretably too often 

 true that the pure-bred sires used in successive generations are not of the 

 same breed, consequently the term grading is to be applied to this sort 

 of breeding with some reservations. Grading is a practice universally 

 commended. Aside from providing a market for a large number of 

 pure-bred sires which would otherwise be sent to the shambles, a desid- 

 eratum which may account for some of the warm advocacy it has 

 received from breeders of pure-bred livestock, it does actually lead to 

 notable improvement when practised intelligently, for pure-bred livestock 

 which has been selected for many generations for particular utilitarian 

 purposes is on the whole very much superior to scrub stock. Moreover, 

 since the proportion of pure-bred animals is very low, it is a positive fact 

 that any considerable improvement must depend upon some method of 

 raising the general level of the great number of inferior animals. 



Perhaps in no line of livestock production are results so readily com- 

 parable as in dairy cattle. Here performance is becoming more and 



508 



