\'ARIABILITV IN EGG WEIGHT 13 



Number of birds 416 



Mean weight at first egg, pounds 5.81 



Standard deviation in weight at first egg ±.55 



Mean annual egg weight, grams 58.30 



Standard deviation in egg weight ±4.08 



Coefficient of correlation .1098 ± .0327 



The Rhode Island Reds used in these studies were large birds with a mean 

 weight of 5.81 pounds at about 190 days of age. Variability in body weight was 

 not excessive and did not exceed 10 percent. The population also showed large 

 egg size, with an average for the year of 58.4 grams (24.7 ounces to the dozen) 

 and a variability of about 7 percent. 



The coefficient of correlation between body weight and annual egg weight was 

 only .1098 + .0327 and barely significant. It seems evident, therefore, that body 

 weight taken at sexual maturity- is a very poor criterion for predicting egg size 

 during the first laying year. 



Correlation Between Body Weight at the End of the First Laying 

 Year and Annual Egg W^eight 



The weights of females at the end of the first laying year are dependent largely 

 upon the mature weight attained at about eleven months of age and the physical 

 condition of the birds. Satisfactory weight at this time is important economically 

 and it is, therefore, desirable to know whether it is correlated with the egg size 

 of the first laying year. The following constants were calculated: 



Number of birds 422 



Mean weight at end of first laying year, pounds 6.28 



Standard deviation In weight at end of laying year. . . ±.83 



Mean annual egg weight, grams 58.32 



Standard deviation in egg weight ±4.11 



Coefficient of correlation —.0578 ±.0327 



Correlation ratio .2312 



Referring back to the previous section, it will be noted that there was an in- 

 crease of .47 pound between the mean weight at first egg and the mean weight 

 at the end of the laying year. The variability in weight was significantly greater 

 at the end of the 3'ear than at the beginning — a condition due largely to variabil- 

 ity in the effect on the birds of a year of laying. 



Regression of annual egg weight on body weight at the end of the year was 

 non-linear, so that the correlation ratio is used to express the a.ssociation. This 

 constant is of a negative order and is significant, indicating that those birds which 

 lay the largest eggs for the year are more likely to be depleted in body weight at 

 the close of the laj-ing year. 



Effect of Age on Egg Weight and Variability in Egg Weight 



The work of many investigators as summarized bj' Jull (1940) indicates that 

 egg weight during the second laying year is from 4 to 8 percent above that of 

 the first laying year. This observation is also in agreement with early observa- 

 tions from this laboratory. The bulk of published data also indicates that there 

 is very little change in egg weight after the second laying year. 



