FACTORS AFFECTING EGG PRODUCTION 3 



With the limited range h\ hatching date, there was no significant correlation 

 between hatching date and annual production although regression was strictly 

 linear. 



Age and Weight at Sexual Maturity 



2. Relation of Age at First Egg to Annual Production 



Age at first egg has served for many years as a valuable unit in selecting for 

 increased egg production. Dryden (1916) was one of the first workers to stress 

 its value. Since the early 1920's early sexual maturity has been widely established 

 in laying flocks. Hays (1924) showed that early sexual maturity is an inherited 

 character and described its mode of inheritance. These observations have since 

 been confirmed by other investigators, including Waters (1934) and Warren 

 (1934). In breeding procedure one of the first steps is to fix genetic early sexual 

 maturity in the flock. 



The Rhode Island Reds used in this study bred true for early sexual maturity. 

 There is, however, considerable variability in the age at first egg. By means of 

 the coefficient of correlation it is possible to determine the relation of variability 

 in age to annual egg production in a flock that breeds true for genetic early sexual 

 maturity'. The following constants appeared: 



Number of birds 1470 



Mean age at first egg — days 189.82 



Age standard deviation ±16.43 



Mean annual production — eggs 213.57 



Annual production standard deviation ±43.38 



Coefficient of correlation —.1534 ±.0172 



Correlation ratio .2264 



In this population breeding true for early sexual maturity there was a sig- 

 nificant negative correlation between age at sexual maturity and annual pro- 

 duction. Regression was found to be non-linear so that the correlation ratio 

 .2264 expresses the association. This figure is in rather close agreement with the 

 simple correlation values, ranging from —.24 to —.44, reported by Kempster 

 (1925) for White Leghorns that did not breed true for early se.xual maturity. 

 These data show why selection for early sexual maturity has been effective in 

 increasing annual egg production. 



3. Relation of Weight at First Egg to Annual Production 



The onset of sexual maturity initiates a new period in the life cycle of the bird. 

 It has therefore been our regular practice to weigh each of the experimental 

 pullets when she laid her first egg. It is also desirable to know whether body 

 weight at this time is associated with subsequent annual production. The follow- 

 ing constants were calculated: 



Number of birds 1465 



Mean weight at first egg — pounds 5.79 



Weight standard deviation ± .54 



Mean annual production — eggs 213.56 



Annual production standard deviation ±43.33 



Coefficient of correlation —.1525 ±.0172 



A mean weight of 5.79 pounds at sexual maturity indicates that the pullets 

 used were large and that weight fluctuations were not very great at this time. 

 Regression was linear and the negative correlation coefifiicient was only .1525. 

 It is very probable that this correlation is brought about by age differences, as 

 pointed out by Hays (1933). 



