MASS. EXPERIMENT STATION BULLETIN 411 



Number of birds 423 



Mean annual variability in egg \\ eight, grams 2.81 



Standard deviation of annual variability +1.00 



Mean age at first egg, days 188.45 



Standard deviation of age at first egg ±21.50 



Coefficient of correlation - .3084 + .0297 



Correlation ratio .4940 



The data show a mean variability in egg weight between the months of 2.81 

 grams, which is much lower than that recorded within any one month as shown 

 in table 1. This fact indicates that the variation within the lot of eggs laid during 

 any one month is greater than the variation between the twelve monthly egg 

 weight means. The standard deviation of the annual variability was 1.0 gram 

 and may be considered very large. Age at first egg is a rather stable genetic 

 character as shown by the mean of 188.45 days, with a standard deviation of 

 only 21.5 da\'s. 



The simple correlation between age at first egg and annual variability in egg 

 weight was —.3084 + .0297. However, the regression of variability on age was 

 found to be non-linear so that the correlation ratio, .4940, expresses the associa- 

 tion. This is a rather intimate relationship and indicates that the younger the 

 pullet is when she lays her first egg, the greater the variability in egg weight 

 between the twelve months of the first laying year. This higher variability in 

 the earlier maturing pullets is probably due in part to the fact that such birds 

 are likely to start their year with small egg size (Hays, 1930). These data further 

 support the idea that extreme early maturity is not desirable from the standpoint 

 of the character of eggs produced. 



Correlation Between March Variability in Egg Weight and Age at First Egg 



As alread\- pointed out, egg weight in this flock reached its maximum for the 

 first year during March, and variability in egg weight was at a low level at this 

 particular time. It is therefore important to know whether there is any correla- 

 tion between the variability in egg size that occurs in March and age at first egg. 

 In this study the individual variability in egg size was measured by the standard 

 deviation within the month and is not the same constant that was recorded in 

 table 1. 



Regression was linear and the following constants were calculated: 



Number of birds 754 



Mean March variability in egg weight, grams 2.05 



Standard deviation of March variability +.75 



Mean age at first egg, days 192.25 



Standard deviation of age at first egg +23.37 



Coefficient of correlation 0080 + .0246 



The population was larger in this study than in the previous section because 

 many individuals had a March egg weight record but lacked other months in the 

 first laying year. 



The coefficient of correlation between March variability and age at first egg 

 is essentially zero, showing that there was no association between age at sexual 

 maturity and variability in egg weight within the month of March. 



