48 
BULLETIN 905, U. S. DEPARTMENT OF AGRICULTURE. 
prepotency is apt to be greater. The pure breeds were founded in 
recognition of the importance of the heredity back of the immediate 
parents, and pedigree, though often misused, is a valuable aid to 
selection, apart from its importance in following a general policy of 
mating. The soundest basis of all for selection of breeding stock 
is the record of past performance as a breeder, provided the record is 
sufficiently extensive to give a fair test. 
The selection of the male, on whatever basis, should not depend 
wholly on the approximation to the ideal which the breeder has in 
mind, but also on the character of the females with which he is to 
be bred. The general rule is that the prospective sire and dam 
Fig. 14.— A striking illustration of the Use of a purebred sire. Two-year-old crossbred Hereford-Jersey 
steer, weighing 1,650 pounds, and his dam, a Jersey cow, weighing 800 pounds. The picture also illus- 
trates the prepotency of the Hereford white face. 
should be chosen so that the average of their characteristics approxi- 
mates as closely as possible the ideal type. In other words, they 
should be alike in characteristics which are up to the standard, while 
defects in one should be balanced by exaggerated development in 
the other. This principle has special application to horse breeding 
in choosing the stallion to breed with a particular mare. In the case 
of cattle, sheep, swine, and poultry its application is necessarily 
more limited, as the same male can not be expected to correct the 
defects of all the females. In these cases the male had best approach 
the ideal type in all respects as closely as possible. If all the females 
are of the same inferior type, however, the use of a male of an exag- 
gerated improved type may lead to most rapid progress. At one 
time the hogs that won the show ring awards were of an exaggerated 
type in which extreme early maturity went with lightness of bone, 
