BREEDING POULTRY FOR EGG PRODUCTION. 12/ 



of the work in 1907. Artificial incubation had to be continued. 

 It would seem that there are two lines of approach to the ques- 

 tion as to whether the failure of the selection experiment to 

 result in increased yields was due to deterioration following 

 artificial incubation. On the one hand may be considered the 

 actual facts regarding other evidence of deterioration besides egg 

 production. While egg production is one index of vitality and 

 constitutional vigor it is by no means the only one. Mortality 

 and morbidity are other indices ; so also is the hatching quality 

 of eggs. Did the flock show evidence of a real constitutional 

 degeneration, as indicated not alone by egg production, but by 

 these other factors as well? 



In considering this whole question it should be recognized 

 that there is a difference between real constitutional degenera- 

 tion and merely a state of temporary low condition due to an un- 

 favorable immediate environment. The one is permanent and 

 the other is only transitory. The one is truly constitutional, the 

 other superficial. This brings us to the consideration of the sec- 

 ond line of evidence which it is possible to get on the problem 

 under discussion. If the real cause of the persistently low egg 

 production during the selection experiment was artificial hatch- 

 ing and rearing merely changing the method of breeding without 

 changing the method of incubation or rearing would certainly be 

 expected to produce no effect. If a purely environmental mat- 

 ter such as artificial hatching and breeding is an efficient check 

 to improvement by one method of breeding, it ought if un- 

 changed to act with equal effectiveness against any other system 

 of breeding. If it does not so act one is forced to the conclu- 

 sion that it was not really an effective factor in determining 

 the results of the first method. 



Let us now turn to the data. In regard to the first line of 

 evidence, namely facts presented l3y other indices of general 

 vigor and vitality besides egg production, adult mortality may 

 be first considered. Table A gives the number of adult females 

 put in the laying house, the number of these which died and 

 the percentage mortality for each of the years covered by the 

 mass selection experiment. The "number of adult females" 

 means the number of pullets put into the laying house each year 

 at the average age of about 6 to 7 months. They are the same 



