INHERITANCE OF INTENSITY 11 



A comparison of data in Tables 4 and 1 shows that mean clutch size and net 

 rate of laying aflford similar measures of intensity. Data in both tables furnish 

 some evidence of inheritance from mothers to daughters. Although the magni- 

 tude of the coefficients of correlation is small, the values are significant and further 

 confirm the importance of selective breeding for high intensity. 



Correlation Between Mothers and Daughters in Annual Egg Production 



Hays (1946) studied this same population with respect to the correlation be- 

 tween mothers and daughters in annual egg production. The work of other 

 investigators was reviewed and the review need not be repeated here. It seems 

 desirable to conclude this study with a brief review of these findings. In the 

 seven-year period mothers produced 1705 daughters with complete annual 

 records. The constants calculated are presented below. 



» 



Number of dams 222 



Number of daughters 1705 



Dams' mean annual egg record 256.73 



Standard deviation of dams' annual records. +27.67 



Daughters' mean annual egg record. 215.97 



Standard deviation of daughters' annual records +42.80 



Coefficient of correlation +.1590 



Correlation ratio .2161 



The greater variability of daughters than of mothers is well illustrated by their 

 respective standard deviations. Regression was non-linear by Blakeman's 

 test. Using 753 degrees of freedom., r should equal at least .098 at the 1 percent 

 level. It may be stated, therefore, that there is a significant correlation between 

 mothers and daughters for annual egg production. The value of this constant 

 is small, so that selection of breeding females on gross annual egg records is far 

 from an exact method. 



When the mean production of all daughters of each family was tabulated 

 against the records of the respective dams, the correlation coefficient was .3064 

 and regression was linear. This confirms that the transmitting ability of a dam 

 is measured by the means of her daughters. 



In general terms, the gross annual egg record of a hen is a rather poor criterion 

 of her breeding ability for egg production. 



SUMMARY 



A population of 2407 daughters hatched over a seven-year period from 237 

 dams has been studied to secure further information on intensity of laying. At- 

 tention was given to the value of clutch size in dams during the four seasons for 

 predicting intensity of their daughters in the same and other seasons. Intraclass 

 correlations for both sires and dams were calculated. Gross and net laying rate 

 records were determined for the four seasons, and gross egg production was also 

 used. The following deductions seem justified: 



1. The simple correlation coefficient between mothers and daughters is not 

 a satisfactory measure of heredity. This method does, however, disclose a sig- 

 nificant association between mothers and daughters for the winter and the spring 

 clutch size. 



2. Dams' spring clutch size appears to be more important than her clutch 

 size at other seasons of the year. 



