174 MAINE AGRICULTURAL EXPERIMENT STATION. IQII. 



PART V. 



Gkne;ral Summary. 

 It is the purpose of this bulletin to present in summarized 

 form the essential results of the experiments in breeding poultry 

 for egg production which have been carried on at the Maine 

 Station during a period of 13 years. These results may be 

 briefly stated here as follows : 



1. An experiment in which the highest laying hens were 

 used as breeders showed that mass selection for high egg pro- 

 duction on the basis of the trap nest record of the individual 

 alone did not, as a matter of fact, result in a steady continuous 

 improvement in average flock production, even though it was 

 continued for a period of ten years. 



2. A further experiment along the same line showed that 

 the daughters of "200-egg" hens with from six to nine years 

 selected ancestry (on the basis of trap nest records) behind 

 them were no better layers, on the average, than birds bred from 

 the general flock. 



3. There is no evidence that either (a) the method of hous- 

 ing, or (b) of feeding, or (c) the fact that the chicks were 

 throughout the period of the exj)eriment hatched in incubators 

 and reared in brooders, or (d) the fact that some degree of in- 

 breeding was i^racticed during the mass selection experiment 

 had anything whatever to do with the outcome of that experi- 

 ment. It is specifically shown in this bulletin that during the 

 period of selection the adult mortality decreased. It is further 

 shown that at the present time, in spite of the fact that there 

 has been no change in the method of hatching and rearing by 

 artificial means, the records of hatching and of chick mortality 

 are such as to give no indication whatever that the strain of 

 Barred Plymouth Rocks which has been used in all the work in 

 breeding for egg production has become in any way deteriorated 

 through the action of environmental or other factors. It is fur- 

 ther specifically shown, by an experiment in out-crossing involv- 

 ing a large number of individuals, that the infusion of new blood 

 into this stock failed to produce any change in the egg produc- 

 tion of the progeny. Such a result makes it impossible to sup- 

 pose that the degree of inbreeding practiced during the mass 

 selection experiment can have had anything whatever to do with 

 the results of that experiment. 



