FACTORS AFFECTING EGG PRODUCTION 9 



Considerable variability was noted in the body weight of the birds and the 

 mean was below the 6.5 pounds stipulated by the American Standard of Per- 

 fection. Regressi*n was non-linear so that the correlation ratio .2183 expresses 

 the association. This is of a negative order and indicates that heavy body weight 

 at the close of the year is likely to be associated with lower antecedent egg pro- 

 duction. 



Simple Regression Coefficients 



Because of the large number of characters included in 'this study, it was not 

 considered expedient to spend the vast amount of labor necessary to calculate 

 the partial and multiple coefficients of correlation. As a partial substitute, 

 the simple regression coefficients are presented for each of the sixteen variables. 

 The regression coefficients in this summary measure the rate of change in annual 

 egg production with respect to a unit change in each individual character. It 

 is recognized that there is considerable overlapping between these characters 

 and that the partial regression coefficients would differ from the simple regression 

 coefficients. It is believed, however, that the values presented furnish reasonably 

 safe guides for breeding operations. 



The mean values for the sixteen different characters as far as known in 1916 

 furnish a starting point. Any differences between these initial means and the 

 means of the birds used in this study represent either progress or retrogression. 

 Table 1 presents the difference between the mean of 1916 and the mean of the 

 present population, the simple regression coefficient of annual egg production 

 on the particular character, and finally the expected increase or decrease in 

 annual egg production. 



Table 1.— Changes in Means, Regression Coefficients, and Expected 

 Changes in Egg Production. 



Character 



Change Regression Expected Increase 



in Coefficient or Decrease in 



Mean Egg Production 



Hatching date weeks -2. +.957 -1.91 



Age at first egg days -40. -.598 +23.91 



Weight at first egg pounds - .28 - 12.200 +3.42 



Winter clutch size eggs +.73 +17.155 +12.52 



Spring clutch size eggs +.46 +11.082 +5.10 



Summer clutch size eggs +.13 +16.993 +2.21 



Fall clutch size eggs +.05 +13.676 +.68 



Winter pause duration days +2.88 —.516 —1.49 



Spring pause duration days —9.15 —.642 +5.87 



Summer pause duration days —1.82 —.657 +1.20 



Number of broody periods —2.14 +.037 —.08 



Annual persistency days +90.80 +.600 +54.44 



Time to standard egg weight. . . .days —57.23 +.186 —10.65 



March egg weight grams +4.24 —1.826 —7.74 



Annual egg weight grams +4.01 +2.569 +10.30 



Weight at end of laying year. . . .pounds -.35 -12.229 +4.28 



Total increase +102.06 



The second column of the table records the change in means between that of 

 the flock hatched in 1916 and the population hatched from 1927 to 1942 and 

 used in this study. In the case of egg weight and time to standard egg weight, 

 the earliest records were taken on the 1927 flock and this mean had to be used as 

 a starting point. 



