BREEDING FOR EGG PRODUCTION 7 



Each pullet was weighed on the day she laid her first egg. The table shows 

 that this mean weight has not fluctuated widely throughout the experiment and 

 that the birds hatched in 1932 were slightly heavier than any other flock except 

 the 1916 flock. This latter flock owes its greater weight to a greater age as Hays 

 (1933a) has pointed out. The data in general indicate that breeding for high 

 fecundity has no significant effect on body weight at first egg. 



The nature of winter pause is fully discussed in a later section of this report. 

 The table shows that the percentage of birds showing a winter pause of four or 

 more days has fluctuated from a minimum of 35.05 in 1921 to a maximum of 

 80.77 in 1925. During the last five years there is some progress apparent in 

 eliminating the trait, but on the whole this character has not responded well to 

 breeding methods used. 



Intensity-, measured by winter clutch size, shows a highly significant improve- 

 ment. This is especially noticeable during the last six years, during which winter 

 clutch size has been used as the sole measure of intensity in the selection of 

 breeders. The mean clutch size in recent years shows that the majority of the 

 birds carry both genes I and I' for large clutch size. 



Broodiness is measured by the percentage of birds broody the first year, by 

 the mean number of broody periods for broody individuals, and by the mean 

 length of broody periods. The data show clearly that broodiness may be greatly 

 reduced by selection of non-broody breeding stock. In the flock of 1916 slightly 

 over 86 per cent of the females became broody in the first laying year, while in 

 the 1932 flock 11.7 per cent exhibited the trait. Quantitatively broodiness as 

 measured by the number of broody periods per broody individual has decreased 

 from an initial mean of 3.5 periods to a mean of 2.1 periods. The mean length 

 of broody periods, measured by the non-productive time interval, remained 

 unchanged throughout the experimental period and ranged very close to 15 

 da\'s. 



Annual persistency within a 365-day laying year has increased significantly 

 during the experimental period. The mean initial persistency was about 248 

 days, and the mean persistency at the close of the experiment about 340 days. 

 The most notable progress since 1920 has been made during the last five years. 

 This increase is due in large measure to the more rigid selection of breeders for 

 greater duration of laying and to the use of more aged breeders with greater 

 length of biological laying year. This latter basis of selection is very effective 

 according to Hays and Sanborn (1933). 



Mean annual egg production stood at about 134 eggs in 1916. It increased 

 rather rapidly to 200 eggs in 1920. The production then remained at the 200-egg 

 level for five years. Beginning with 1925, the trend has been upward to the 

 highest mean of 234 in 1931. Production has not advanced a little each year 

 but has increased by rather abrupt advances at intervals accompanying the 

 establishment of a desirable character in a large percentage of the flock. Atten- 

 tion is called to the fact that these egg records represent the mean of all normal 

 birds in each family that lived to complete a 365-day record, and that no culling 

 was done during the laying year. 



Mortality in the laying houses has varied widely throughout the period re- 

 ported. The records do not show that mortality has increased as the breeding 

 work progressed and as the egg production level was raised. Records during the 



