HEREDITARY AND ENVIRONMENTAL FACTORS 

 AFFECTING VARIABILITY IN EGG PRODUCTION 



By F. A. Hays, Research Professor of Poultry Husbandry 



INTRODUCTION 



It is a well-known fact that both hereditary and environmental influences 

 affect the number of eggs laid by a hen. Evidence is not conclusive on many 

 points, however, and experimental data have not been reported to furnish 

 information concerning the quantitative variation of specific fecundity traits 

 from generation to generation. There is at present an outstanding need of a 

 clear-cut distinction between the effects on fecundity of heritage and environ- 

 ment. Such a problem offers many difficulties, the most outstanding of which 

 is the lack of any measure of fecundity in males. 



This report concerns itself with results obtained in carrying three lines of 

 birds through four generations. Consideration is given to variability in five 

 inherited fecundity characters; sexual maturity, intensity, winter pause dura- 

 tion, total days broody, and persistency. 



The variability in winter and annual egg records is also reported. Such 

 environmental influences as hatching date, increase or decrease in body weight, 

 and daily house temperature are considered in relation to egg production and 

 the relative importance of each is discussed. 



PLAN OF EXPERIMENT 



1928 Matings 



In the spring of 1928 three pens of yearUng hens were selected for this experi- 

 ment. Pen A consisted of six hens from three unrelated families mated to an 

 unrelated yearling male. The breeding females and the male were chosen with 

 special reference to uniformity within the family for age at first egg, length of 

 winter pause, intensity, days broody and persistency. 



Pen B contained two unrelated yearling hens. These two hens came from 

 famihes that were especially uniform in annual egg records. The male used in 

 this pen was a half brother to one hen and not related to the other. His sisters 

 were very uniform in annual egg records. 



Pen C included four yearling hens from three families that had very high 

 annual egg records. Three of the hens were half-sisters and the fourth was un- 

 related. These half sisters were mated to their half brother and the unrelated 

 hen was not related to this male. 



1929 Matings 



Selection of breeding stock in 1929 to produce generation three in Pen A 

 was on the basis already indicated, of family uniformity in the second genera- 

 tion of this line. Since pullet breeders were used, it was only possible to consider 

 in selection, age at sexual maturity, intensity and winter pause. The male was 



