248 PRACTICE OF POULTRY BREEDING 
The chief advantage of inbreeding is the possibility which it 
offers of fixing or making permanent the blood of some valuable 
individual. In-bred progeny are exceptionally potent. Another 
advantage is that it avoids the introduction of new blood which 
might produce objectionable characteristics. Inbreeding is the 
greatest force known to intensify existing blood lines, and this 
factor makes it one of the best as well as the worst system to use; 
for it intensifies all characteristics of the individual, whether bad 
or good. Therefore the breeder who resorts to this method of 
mating must exercise special care in eliminating objectionable 
factors which would be intensified equally with the good ones. 
It is often supposed that inbreeding tends to reduce vigor and 
vitality; but, when this is the case, it is undoubtedly due to the 
fact that these characteristics exist already and are intensified in 
the progeny. If poultry breeders were more careful in selecting 
for vigor and vitality, this apparent objection to inbreeding would 
be overcome and less heard of. 
Line Breeding.—Line breeding may be defined as the breeding 
of individuals which are selected from, or restricted to, a single 
line of descent. For example, it is the process of breeding within 
one family or within a limited number of families all of which 
have a common ancestry and represent similar types (Fig. 126). 
Line breeding offers good opportunity for improvement, since 
it excludes everything outside of the chosen line of descent and 
combines in the progeny the characteristics especially desired. 
The result is the rapid purification of the pedigree and the fixing 
of atype. There is slight danger of outside or alien traits appear- 
ing. This is a very conservative system of breeding, and is the 
one practised by many of the best poultry breeders. It has resulted 
in building up some of our best strains of standard-bred poultry. 
The leading advantages of line breeding are two: (1) The probable 
certainty with which results may be predicted, thus allowing the 
breeder to work with his eyes open; (2) the progeny of line-bred 
birds are backed up by a strong hereditary influence which results 
in hastening improvements in the one desired direction, owing to 
the lack of alien or mixed blood. 
In practising line breeding there is one point of caution,— 
namely, the necessity of making the matings both from the pedi- 
gree records and by individual selection in the pens. Some breeders 
are apt to neglect the latter factor of individual condition, and 
make their matings from paper only; in consequence, a few genera- 
