10 MASS. EXPERIMENT STATION BULLETIN 344 



Daughters in lines A and B showed an upward trend in egg size as the experi- 

 ment continued. In line C there was no improvement in the last four genera- 

 tions. The daughters of line C did not increase, because their dams were for 

 the most part of the medium phenotype. In line B the generations of daughters 

 hatched in 1934 and 1935 exhibited in a pronounced way the breeding ability 

 of sires and dams that belong to the large-egg type. Line B affords a good 

 illustration also of the breeding value of dams in the medium-egg-size group. 



All of the daughters produced in the three lines were grouped in a frequency 

 distribution and tested for normalcy of sample. The X 2 test for each of the 

 three lines indicated them to be satisfactory samples for statistical study. 

 The mean hatching-season egg weight was as follows: 



Line A, 56.84 ± .182 grams (24.1 ounces to the dozen) 

 Line B, 58.78 ± .205 grams (24.9 ounces to the dozen) 

 Line C, 58.92 + .211 grams (25 ounces to the dozen) 



The difference in mean egg weight of lines A and B was 1.94 ± .274 grams, 

 which is a significant difference. The difference in means of lines B and C was 

 .14 ± .294 grams, which is insignificant. These data agree with the observa- 

 tion on winter egg weight in section A. The fact is evident in this experiment 

 that the method of selective breeding used did produce a significant difference 

 in hatching-season egg weight between lines A and B, but not between lines B 

 and C. 



G. Studies on Annual Egg Weight 



Annual egg weights used here represent the mean of twelve monthly averages, 

 beginning with October of the pullet year and ending the following September. 

 Every egg was weighed to the nearest gram when taken from the trapnest. 

 The data are handled separately for the three lines. 



Mean Monthly Egg Weight by Lines 



Table 1 presents the mean monthly egg weights for the three lines, including 

 the last five generations. Complete data on the generations hatched in 1928, 

 1929, and 1930 are not available. 



Table 1. — Mean Monthly Egg Weight by Lines, 1931-1935 



Line A is represented by 122 birds, line B by 120 birds, and line C by 106 

 birds with complete annual egg-weight records. The table shows that maxi- 

 mum egg weight occurred in March in all three lines. It should be noted that 

 the September egg weight of line A was as high as the March weight. These 

 data point to the maximum egg weight of the pullet year occurring during the 

 sixth laying month, preceded by a rather consistent rise from the first pullet 

 egg and followed by a decline in April and May. During June, egg size began 

 to recover and during September it approached the March level. 



Mean yearly egg weights were calculated by taking the average of the sum 

 of the individual yearly weights, and were as follows: 



