HYBRIDIZATION IN ANIMAL BREEDING 513 



must necessarily depend to a considerable extent upon the care used in the 

 selection of the female breeding stock. A standard of excellence should 

 be established for them as well as for the sires, and any which fall below 

 that standard when subjected to a fair trial should be promptly eliminated 

 from the breeding herd. The standard should be so high that only the 

 very best females in the herd will be retained, it should consequently 

 be raised gradually as the excellence of the herd increases. The breeder 

 should guard jealously against disposing of his best female stock. 



When all this has been done the question naturally arises, through 

 how many successive generations is it necessary or advisable to use 

 pure-bred sires? To this question only a general answer can be given. 

 Improvement in grading is at first rapid and in successive generations 

 becomes less and less rapid as the grade stock approaches more and more 

 closely to the standard of excellence of pure-bred stock. Practically, it 

 appears to be true that four or five generations of grading, particularly 

 if rigid selection of both sires and dams be practised, is sufficient to bring 

 the standard of utilitarian excellence up to that of the pure-bred animal. 

 After that it is a very grave question whether further employment of 

 pure-bred sires is either necessary or desirable, provided it is possible to 

 select a sire from a large number of high-grade animals. To effect 

 improvement in utilitarian excellence in such herds requires sires of very 

 superior excellence, and, if pure-bred, they would usually be too expensive 

 for use in grade herds. On the other hand, it is possible among a large 

 number of grade animals to select a sire from a superior line of grade 

 stock, which would perhaps not be surpassed in utilitarian excellence by 

 any pure-bred animal. Such grade animals do not have an inflated value 

 on account of their breeding. They come within the price standards of 

 sires which may be used in improving grade stock. It is also an open ques- 

 tion whether more actual improvement may not be effected in high-grade 

 stock of superior excellence by selection within it, rather than by further 

 top-crossing to pure-bred sires. There is some probability that such stock 

 may be more variable and consequently possess greater potentialities 

 for improvement than the pure-bred stock itself. It is a matter of regret, 

 however, that grading has not progressed far enough in very many cases 

 to make it necessary to consider this problem. As a general rule, there- 

 fore, it is best, if possible, to continue breeding to the best pure-bred sires 

 which are available. 



In the early days of breed improvement provision was made for admit- 

 tance to record of animals which were the result of top-crossing several 

 times to pure-bred sires, and the question often arises whether this should 

 be resumed, inasmuch as present day livestock associations with only 

 unimportant exceptions make no provision for entry of any animal that 

 is not the offspring of recorded animals. Fad and fashion play a large 



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