BREEDING POULTRY FOR EGG PRODUCTION. 1 75 



4. In the laying year 1907-08 a new plan of breeding was 

 adopted as a working hypothesis to be tested by experiment. 

 This plan is based on the employment of individual pedigree 

 records and has its theoretical foundation in the genotype con- 

 cept of Johannsen. This working hypothesis is fully explained 

 in Part III of the present bulletin. It involves the following 

 factors : 



(a) That the egg record of an individual hen gives no 

 ■definite indication whatever as to what the probable laying 

 of her daughter will be. Examination of hundreds of pedigree 

 records leaves no doubt as to the truth of this fact. Individual 

 Ibirds with high egg records are as likely as not to produce 

 daughters that make poor egg records and vice versa. From 

 the laying record of an individual hen it is quite impossible for 

 anyone to tell whether its progeny will be good layers or poor 

 la3^ers. 



(bj A flock of hens, no matter how "pure bred" it may be, 

 is really not a homogenous, unitary aggregation, but instead it 

 is made up of a varying number of lines or strains, each of 

 which tends to breed true to a certain or definite degree of egg 

 productiveness or fecundity. In other words such a flock is a 

 mixture of several component lines. The individuals in each 

 hne tend to produce ofifspring true to the type of the line rather 

 than to the type of the population as a whole, exce]3ting in cases 

 where by chance the population type and the type of one or 

 more lines happen to be the same. 



(c) When mass selection alters the population type it does 

 so by a process of isolating from the mixture certain strains 

 whose own types are different from the original general popu- 

 lation type and .which dift'er in the direction toward which 

 selection is made. The thing to be sought then in the practical 

 breeding of poultry for increased egg production is to discover 

 by means of pedigree analysis those individuals of the general 

 flock which possess high fecundity in inheritable form. These 

 individuals may then be isolated and propagated and im]n-ove- 

 ment thus brought about. 



5. It is shown that by the application of this new plan of 

 breeding it has been possible to isolate from the same stock of 

 birds, which was used in the mass selection experiment, pedi- 



