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 gradestock. 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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