8 MASS. EXPERIMENT STATION BULLETIN 344 



Correlation Between Winter Egg Weight and Annual Egg Weight, by Lines 



Regression of annual egg weight on winter egg weight was strictly linear. 

 The coefficients of correlation were as follows: 



Line A, + .8495 ± .0162 



Line B, + .8823 ± .0125 



Line C, + .8775 ± .0133 

 These constants indicate that more than 75 percent of the variation in annual 

 egg weight is associated with variation up to January 1. Birds that are to 

 average 56.7-gram eggs (24 ounces to the dozen) for the year should lay 54- 

 gram eggs (23 ounces to the dozen) up to January 1. 



B. Studies on Hatching-Season Egg Weight 



Hatching-season egg weight was determined during February and March of 

 the pullet year. At this time the birds had been laying for about five months 

 and were between ten and eleven months old. According to previous data 

 (Hays, 1910), maximum egg weight for the pullet year occurs in February. 

 A study of egg weight during this period should furnish valuable information 

 to the breeder. 



Correlation Between Hatching-Season Egg Weight and Annual Egg Weight, by 

 Lines 



Regression of annual egg weight on hatching-season egg weight was linear. 

 The coefficients of correlation were as follows: 



Line A, + .9111 ± .0104 



Line B, + .9261 ± .0088 



Line C, + .8004 ± .0225 

 These constants show that more than 77 percent of the variation in annual 

 egg weight is associated with variation in the hatching season. The regression 

 constants further show that on the average the hatching-season egg weight of 

 the pullet year must be about 58.2 grams (24.7 ounces to the dozen) if such 

 birds are to average 56.7 grams (24 ounces to the dozen) for the full pullet 

 laying year. 



Hatching-Season Egg Weight of Parents and Daughters 



There can be no specific method for measuring egg size in males, but a record 

 of the egg size of their full sisters does throw some light on their possible geno- 

 type. Complete records are available on the dams used. Chart 2 illustrates 

 graphically the hatching-season egg weight of sisters of sires, of dams, and of 

 daughters in the three lines throughout the experiment. All egg weights were 

 made during the pullet laying year. 



The mean egg weight of the sisters of the sires used throughout the experi- 

 ment shows a rather consistent increase as the experiment progressed. There 

 is high probability that the sires during the last three years may have belonged 

 to the large-egg phenotype. Evidently these brothers were not homozygous 

 for genes B and C, because they did not breed true in any of the three lines. 



The dams in line B apparently represent a fortunate selection as far as egg 

 size is concerned. In contrast, the dams of line C were scarcely as good at the 

 end of the experiment as at the beginning. Here is further evidence of the 

 difficulties in developing the large-egg phenotype. If the large-egg phenotype 

 did not depend on the cumulative action of genes B and C, there would have 

 been less difficulty. 



