WINTER CYCLK AND WINTER PAUSE 



171 



tion between age at first egg and k-ngtli of the winter laying cycle. Class 

 intervals of ten days have been used for age, and the respective ages of the 

 individuals tabulated against their winter cycle length. The constants de- 

 termiiuHl ave as follows: 



Number of birds .... 

 Mean age at first egg . 

 Age at first egg standard deviation 

 Mean length of winter cycle 

 Winter cycle standard deviation . 

 Coefficient of correlation 

 Regression of age on winter cycle 

 Regression of winter cycle on age 



Age at first egg varies within moderate limits. Since genetically-early 

 and genetically-late birds are concerned, and because environment probably 

 modifies age and sexual maturity, tiie standard deviation of age is not ex- 

 cessive. 



A significant negative correlation is shown, as might be anticipated from 

 the constants obtained in section 2. Age of sexual maturity may be classi- 

 fied as a characteristic influencing the length of winter cycle as determined 

 by the onset of winter pause. Here is an example of a heritable trait being 

 negatively correlated with duration of winter c\cle. 



(c) Reldllon of Winter Cycle to E(fy Production. 



A knowledge of the relation of winter cycle length to winter fecundity 

 and annual fecundity is of value for prediction purposes. If any short-time 

 measure of fecundity that is reasonably accurate in predicting winter and 

 annual production is discovered, it will be of much economic import. Proper 

 culling enables the poultryman to raise mean flock production by disposing 

 of mediocre layers. If a relatively short season of trapnesting gives a clue 

 to probalde jirodiiction for tiie year, such information will greatly assist 

 poultrymen. This section considers the correlation between length of winter 

 cycle and winter prtxluction and length of winter cycle and annual produc- 

 tion. Since the winter cycle length for each bird is tabulated against her 

 egg record, a true measure of degree of correlation is arrived at. 



ft 

 4- Correlation Between Length of Winter Cycle and Winter Ei/g Record. 



Both length of winter cycle and winter egg record are placed in class 

 intervals of ten for the 2078 indivi(hial pullets studied. The following con- 

 stants were determined: 



Number of birds 



Mean length of winter cycle 



Winter cycle standard deviation 



Mean winter production 



Winter production standard deviation 



Coefficient of correlation 



Regression of winter cycle on production 



Regression of production on winter cycle 



2078 



52.26 

 ±34.23 



56.99 

 ±23.40 



+.6538 ±.0085 

 -f.956 



+.4-47 



