170 



TECHNICAL BULLETIN 8 



A significant negative coefficient of correlation informs that, in general, 

 early-hatched pullets have a longer winter laying cycle than late-hatched 

 pullets of the same flock. The magnitude of tlie constant does not establish 

 an intimate relationship, however, and for this reason the influence of other 

 forces is evident. An increase in length of laying cycle is important from 

 the breeding standpoint, because it signifies a greater mean winter record, 

 and winter production is intimately correlated with annual production (Hays, 

 Sanborn and James, 1924). 



2. Correlation Belxceen Date of First Egg and Length of Winter Cycle. 



Date of first egg is very important economically. Its significance biolog- 

 ically depends upon the influence of weather conditions on egg production. 

 Specific data concerning the influence of weather on fecundity are not avail- 

 able, however. There is a considerable body of evidence pointing toward a 

 seasonal periodicity of production which has led a number of workers to 

 consider winter, spring, summer and autumn cycles of laying. 



In this experiment 2078 pullets with definite winter cycles are available for 

 study. Fifteen-day class intervals are used in grouping data of first egg, 

 and the range in dates is August 24 to February 20. Below are the con- 

 stants calculated: 



Number of birds 2078 



Mean date of first egg (Oct. 29) ... . 5.93 



Date of first egg standard deviation .... ±2.09 



Mean length of winter cycle ..... 52.26 



Winter cycle standard deviation ±34.23 



Coefficient of correlation — .5307 ± .0106 



Regression of date of first egg on winter cycle . — .032 



Regression of winter cycle on date of first egg . — 8.689 



The date of first egg fluctuates widely in tiie population studied. The 

 mean date of first egg for the 2078 birds studied is October 29. In breed- 

 ing for fecundity this variability in time of beginning to lay may be reduced 

 genetically and also by providing a more uniform environment. 



A negative coefficient of correlation of substantial magnitude demonstrates 

 that early laying makes for a long winter cycle. The relation that winter 

 cycle length holds to egg production remains to be considered in sections 

 4 and 5 of this report. 



(b) Relation of Heritable Traits to Winter Cycle. 



Age at first egg is a definitely heritable trait (Hays, 1924). It has been 

 shown by a number of workers to be intimately correlated with both winter 

 and annual fecundity. This study shows how age at first egg is related to 

 length of the winter laying cycle. Sexual maturity is the only heritable 

 characteristic reported on in relation to winter cycle. 



3. Correlation Between Age at First Egg and Length of Winter Cycle. 

 The same group of 2078 pullets has been studied to ascertain the correla- 



