14 MASS. EXPERIMENT STATION BULLETIN 359 



Comparing mean fertility with the percentage of unsuccessful matings gives 

 some interesting information. The percentage of unsuccessful matings indicates 

 the relative number of incompatible matings due either to the failure of the birds 

 to mate or to the incompatibility of sperm and ova. Mean fertility is governed 

 largely by the number of such unsuccessful matings. Son-mother matings were 

 very successful as measured by limited data. Half-brother-sister matings were 

 also generally successful, but sire-daughter matings gave 14 percent of failures. 

 In the outbred males, W and S were entirely successful. The T stock gave com- 

 plete compatibility for the first ten years. The matings from 1933 to 1936, made 

 three weeks earlier in the season, gave the same percentage of failures as did all 

 brother-sister matings. Outside stock P gave fewer failures than the check group, 

 but was inferior to all other outside stock and to most inbred matings. 



8. Correlation Between Mothers and Daughters in Fertility 



Considering the character of the data available, the best measure of the pos- 

 sible inherited nature of fertility is the coefficient of correlation for fertility of 

 mothers and daughters. Omitting inbreds and outbreds, data were available on 

 466 mothers producing 1,452 daughters with fertility records. In the tabulation 

 each mother was paired against each of her daughters. Daughters with zero 

 fertility were included in the tabulation. The constants derived were as follows: 



Number of mothers 466 



Number of daughters 1452 



Mean fertility of mothers, percent 89.31 



Mothers' fertility standard deviation ±12.91 



Mean fertility of daughters, percent 71 . 83 



Daughters' fertility standard deviation +33 . 20 



Coefficient of correlation 0209 + .0177 



Mean fertility of mothers was significantly higher than that of their daughters, 

 partly because 157 daughters had zero fertility. When these 157 daughters are 

 omitted, the mean fertility of the daughters was 80.54 percent, still significantly 

 below that of the mothers. Standard deviation in fertility was much greater in 

 daughters, whether the zero class was included or not. This standard deviation 

 is exaggerated in the daughters because there were more than three times as many 

 daughters as mothers. 



The coefficient of correlation in fertility between mothers and daughters is 

 so near zero as to be insignificant. Regression was found to be linear. The in- 

 significant value of the coefficient of correlation indicates that factors other than 

 inheritance control fertility and that selective breeding to improve'fertility would, 

 therefore, be ineffective. 



Summary 



A study was made of 2,101 Rhode Island Red females and 305 males used in 

 pedigree matings from 1922 to 1936 to secure information on various factors 

 that might affect fertility and to discover whether fertility is an inherited trait. 

 From the data available, several conclusions may be drawn: 



1. Outside temperature during the period that hatching eggs are laid had a 

 specific effect on fertility. When the average temperature was below 32°, average 

 fertility ranged between 54 and 77 percent. When the temperature rose to above 



