246 PRACTICE OF POULTRY BREEDING 
BREEDING SYSTEMS. 
Crossbreeding or Hybridizing.—Crossbreeding may be defined 
as the breeding together of birds of different breeds, varieties, 
or families, with the hope of securing progeny exhibiting in one 
individual the desirable characteristics of both parents. This form 
of breeding is only applicable in the formation of new breeds. 
The effect of its use is so thoroughly to mix blood lines and pedi- 
grees that all records of the performances of the ancestry are lost 
or of no value. Crossing is one of the most certain means of pro- 
ducing variability. 
Where birds possessed of similar characteristics are mated 
together, the progeny of the first cross usually show a fair degree 
of uniformity with regard to the desired trait. Further breeding 
of this crossbred progeny, or hybrid, will result in a great variety 
of types and variations in the characteristics. 
When birds of opposite or unlike characters are mated together, 
the results are varied and disappointing, even in the first generation. 
A good rule is to avoid crossing wherever possible, and to 
resort to it only as the last extreme toward a definite aim. 
Grading up is a term applied to a method quite generally used 
to improve the quality and characters of a mongrel flock. This 
is usually accomplished by the use of pure-bred males in a mixed 
flock. The resulting progeny are called grades, since they are the 
offspring of a pure-bred animal and one of mixed or common breed- 
ing. In poultry raising the cost of birds which arepure bred and true 
to type is relatively so small, in comparison with their superiority 
over mixed stock, that, as arule, it is more satisfactory and econom- 
ical to begin with pure-bred birds, and if need be to start with but 
asmall number. Where grading up is practised, the mating may 
be made either way, but the male is generally taken for the pure- 
bred parent, since he represents half the flock as far as progeny are 
concerned. By this method it is possible to raise a practically 
pure flock from mongrels in a certain number of generations. 
The great disadvantage of grading up is the fact that it is not 
likely to be closely followed continuously after a certain degree 
of perfection is reached, and, just as soon as the breeder uses a 
grade male bird, improvement ceases and retrogression begins. 
Inbreeding.—The terms inbreeding and in-and-in breeding 
are used to designate the breeding together of animals which are 
of the same pedigree. Inbreeding commonly means the mating 
