8 MASS. EXPERIMENT STATION BULLETIN 301 



7. Degree of Broodiness Measured by Number of Broody Periods 



One of the most satisfactory measures of degree or intensity of broodiness is 

 the number of distinct broody periods during the laying year. In the studies 

 reported here, degree of broodiness was recorded on all individuals during the 

 pullet laying year, which begins with the first egg laid and ends 365 days later. 



Table 7 gives the mean number of broody periods each year for the two lines 

 throughout the experiment and the mean for the entire experimental periofi. This 

 table includes only individuals that became broody and not the entire population. 



The data in table 7 show very clearly that the degree of broodiness was higher 

 in the broody line. Without exception, year after year, the mean number of broody 

 periods per broody bird was smaller in the non-broody line. There w-as also a 

 slight tendency for degree of broodiness to decrease in succeeding generations in 

 the non-broody line. The broody' line, however, does not exhibit a significant 

 change in degree of broodiness. 



The coefficients of variation for the two lines do not indicate a decrease in 

 variability throughout the experiment. This fact suggests that degree of broodiness 

 is affected by environmental influences, although at the present time there is no 

 definite information as to just what these environmental factors may be. 



The mean number of broody periods for the two lines in the nine year period 

 was 2.63 +.16 and 3.99+. IL The difference amounts to L36+.19 and is clearly 

 significant. The data in table 7 as a whole show that the degree of broodiness in 

 the non-broody line was distinctly less than in the broody line. 



Table 7. — Broody Periods for Broody Birds 



8. Degree of Broodiness in Daughters from Various Classes of .Mothers 



The intensity of broodiness in all daughters from mothers with varying degrees 

 of broodiness is considered to throw light on the inheritance of degree of broodiness 

 The broody line alone was used in these studies and the dams showed from one to 

 eleven broody periods during their first laying year. Table 8 presents the detailed 

 data. 



The mean number of broody periods in ail daughters from dams ranging in 

 degree of broodiness from one to eleven broody periods showed a rather consistent 

 increase as would be expected in an inherited character. The mean number of 

 broody periods in daughters from the eleven different classes of dams when fitted 

 to a straight line showefl the difference in number of broody periods between all 

 daughters of hens broody once and those broody eleven times to be L20 periods. 

 Tested by the X^ test for goodness of fit the straight line was found to fit the data. 



