12 MASS. EXPERIMENT STATION BULLETIN 344 



Line A, 56.15 + .205 grams (23.8 ounces to the dozen) 

 Line B, 58.30 ± .247 grams (24.7 ounces to the dozen) 

 Line C, 57.03 ± .235 grams (24.2 ounces to the dozen) 



The data show in general that eggs laid during the montn of maximum weight 

 average about 4 percent heavier than the mean for the pullet year. The birds 

 in line A did not average standard egg weight until January: those in line B 

 averaged standard egg weight in November, and those in line C sometime in 

 December. Each line was checked for normalcy of sample by the X 2 test and 

 all gave a high probability of normalcy, the lowest probability being .6314. 

 The differences in the means may be checked against the probable error of 

 difference. Line B had a mean annual egg weight 2.15 ± .321 grams greater 

 than line A. This is a statistically significant difference. The difference be- 

 tween lines A and C was .88 + .312 gram, and is of doubtful significance. 

 Line B had an annual egg weight 1.27 ± .341 grams heavier than line C. Here 

 is a significant difference in the reverse order of expectation. These results 

 may be partially explained on the basis of female ancestry, as shown on Chart 3. 



Progress in Breeding for Egg Size 



Annual egg records of mothers and daughters are summarized in Chart 3, 

 which presents in graphic fashion the mean annual egg records of mothers used 

 to produce daughters in each year in the experiment. 



In line A there was a rather consistent increase in egg weight of daughters 

 as the experiment continued. Dams for breeding in 1934 and 1935 were selected 

 on the basis of time to standard egg weight rather than upon a particular egg 

 weight basis. These dams ranged from 61 to 90 days in time required. A 

 superior group of dams resulted in 1934 but the 1935 dams showed inferior 

 annual egg weight. Complete annual egg weight records are not available on 

 the first two generations of dams and only part of their daughters had egg weight 

 records throughout the year. 



There was a remarkably consistent increase in mean annual egg weight in 

 both mothers and daughters of line B through eight generations. The last two 

 generations of mothers reached standard egg weight in 31 to 60 days. In annual 

 egg weight these mothers fell below the previous generation of mothers that 

 were selected on the basis of 57-gram eggs in November. The last two gener- 

 ations of daughters paralleled these dams in annual egg weight. 



Line C dams showed an increasing annual egg weight for five generations. 

 When the basis for selecting dams in this line was changed in 1934 to those 

 reaching standard egg weight in to 30 days there was a decline. The daughters 

 in this line began to decline in 1933 when their dams were chosen on the basis 

 of 59-gram eggs in November. The general behavior of line C suggests the 

 epistatic nature of a gene for small egg size combined with chance selection 

 of males transmitting small egg size in this line. The data indicate further 

 that there is no advantage from the standpoint of annual egg weight in selecting 

 breeding females laying heavier than 24-ounce eggs in November if they are 

 to be used for breeding in March and April. 



