WINTER CYCLE AND VVINIEU 1>ALISE 1 77 



A definite and sipnifieant correlalion exists i)ctween early laying and tlie 

 presence of winter i)ause. Ihis tact snjrgests tiie importance of breeding for 

 a specific age at first egg, and liatcliing on some special dale to meet condi- 

 tions of environment. 



(b) Inherited I'haracterislks Concerned With Fecundili/ In 

 Relation to Winti'r Pause. 



In tiie category of inherited fecundity traits tiiat may be considered in their 

 relation to winter pause, tb.e following may be grouped: age at first egg, 

 weight at first egg, winter rate or intensity, length of winter cycle, size of 

 winter clutch, annual rate or intensity and annual persistency. A study of 

 the relative degree of correlation l)etween these inherited characteristics and 

 duration of winter pause as well as its presence or absence furnishes con- 

 structive information in breeding for high egg yield. Such analyses bring 

 out important relationships as well as pointing out possible cases of genetic 

 linkage. 



]1. Correlation Between Aye at First Egg and Length of Winter Pause. 



Age at first egg marks sexual maturity in the pullet. Age at first egg is 

 inherited in Mendelian fashion according to Hays (loc. cit.). The importance 

 of early laying to high winter and annual egg yield has been stressed in our 

 publications as well as in those of other workers. The significance of know- 

 ing if there is a correlation between age at first egg and duration of winter 

 pause is therefore very evident, since both are inherited traits and both are 

 concerned in winter and annual egg yield. A study was therefore made on 

 the 2134 pause birds already considered in sections 7 and 9. Age at first 

 egg class intervals of ten days are used and the same class interval used for 

 length of winter pause. The following constants were calculated: 



Number of birds 2134 



Mean age at first egg 203.26 



Age at first egg standard deviation .... ±26.28 



Mean length of winter pause ..... 32.26 



AVinter pause standard deviation .... ±21.92 



Coefficient of correlation — .2329 ± .0138 



Regression of age at first egg on winter pause . . — .279 



Regression of winter pause on age at first egg . . — .194 



The above coefficient of correlation is almost identical with that between 

 hatching date and winter pause duration given in section 7. The range in 

 hatching date covers 49 days, while the range in age at first egg covers 180 

 days. The fact therefore becomes evident that a slight change in hatching 

 date would cause a greater change in winter pause duration than would the 

 same change in age at first egg, as brought out by their respective regres- 

 sion coefficients. Herein lies the reason for emphasizing hatching date as of 

 greater significance in relation to winter pause than age at first egg when 

 they exhibit identical coefficients of correlation to winter pause durntion. 



