10 MASS. EXPERIMENT STATION BULLETIN 423 



Some significant changes in means may be observed. Hatching date has been 

 changed to two weeks earlier in the recent flocks and this is a handicap as far as 

 annual egg production is concerned. Age at first egg has been reduced 40 days 

 and this favors increased egg production. Body weight at first egg has been 

 decreased about .28 pound largely because of earlier sexual maturity. Intensity 

 has been greatly improved in winter, as clutch size shows. Spring intensity has 

 been somewhat increased, but summer and fall intensity show little improvement. 

 Pause duration has increased slightly in birds exhibiting winter pause. There has 

 been considerable reduction in the length of spring pauses but only a slight 

 reduction in length of summer pause. The number of broody periods has greatly 

 declined in the few birds that exhibit broodiness. Annual persistency shows a 

 remarkable increase of almost 91 days. Time from first egg to standard egg 

 weight has declined almost two months. Egg weight in March and egg weight 

 for the entire first year have increased by about 4 grams for each egg, about 14 

 percent. This is equivalent to an increase of about 1.7 ounces to the dozen. 

 Body weight at the end of the first laying year has declined about .35 pound. 



Regression coefficients in the third column of the table record the rate of change 

 in egg production associated with unit changes in each character. 



The figures in the last column of the table were obtained by multiplication of 

 columns two and three. For example, hatching date has been changed to two 

 weeks earlier than it was in 1916. Since early hatching tends to reduce annual 

 egg production, we should expect that change to reduce the mean annual egg 

 record slightly. The table shows, an expected reduction of 1.91 eggs. Other 

 changes in means that would be expected to be accompanied by a decrease in 

 annual egg production were winter pause duration, number of broody periods, 

 time to standard egg weight, and March egg weight. Winter pause duration 

 probably had little effect because there was a tendency for the percentage of 

 birds with winter pause to decrease. The percentage of birds exhibiting broodi- 

 ness was so small that any change in the number of broody periods would have 

 little effect on the flock as a whole. 



A number of changes in means have had a very significant effect in increasing 

 the annual egg record. Among these are age at first egg, winter clutch size, 

 annual persistency, and probably annual egg weight. There was very little 

 change in such characters as summer and fall clutch size, spring and summer 

 pause duration, and body weight at the end of the laying year. 



An examination of the size of the regression coefficients indicates that intensity 

 as measured by clutch size at different seasons of the year is extremely important. 

 Since summer and fall clutch size did not change significantly between 1916 and 

 the recent period, it seems very probable that these two should be given special 

 attention if egg production is to be increased. Spring pause and summer pause 

 are not very important, yet they too should be considered in selective breeding. 

 Egg size in the population studied has attained a satisfactory level with the 

 average time required to reach a 24-ounce level about 50 days, and the mean 

 annual egg weight was 58.51 grams or 24.8 ounces to the dozen. Very likely body 

 weight at the close of the first la\ing year should not be further reduced. 



When the combined estimated effects of these sixteen characters is summed up 

 at the bottom of the fourth column, an approximation of what the mean egg 

 record of the 1937 to 1942 flocks should be is arrived at. The mean annual egg 

 record of the 1916 flock was 134 eggs (Hays and Sanborn, 1939). The mean 

 annual record of the 1470 birds hatched from 1937 to 1942 was about 214 eggs. 

 Adding the expected increase of 102 eggs to the original 134 gives a value of 236. 

 Thus the actual average production lacks 22 eggs of expectation. It is interesting 

 to note that the flock hatched in 1942 averaged to lay 233 eggs. 



