FACTORS AFFECTING EGG PRODUCTION 5 



7. Relation of Fall Clutch Size to Annual Production 



Fall clutch size was calculated for the months of September and October 

 at the close of the first laying year. This constant should not be confused with 

 the number of eggs laid during August and September as a measure of persistency 

 suggested by Knox, Jull and Quinn (1935). Fall clutch size was tabulated against 

 annual production to obtain the following constants: 



Number of birds 1297 



Mean fall clutch size — eggs 2.21 



Fall clutch size standard deviation ±1.24 



Mean annual production — eggs 218.83 



Annual production standard deviation ±41.13 



Coefficient of correlation +-3063 ±.0170 



Correlation ratio .4122 



The mean fall clutch size 2.21 indicates that the birds were laying at a slow 

 rate toward the end of the year. It is believed, however, that rate of production 

 near the end of the year is important. Regression was non-linear and the cor- 

 relation ratio .4122 expresses the association. While rate of laying at the close 

 of the year is less important than winter, spring, or summer rate, it does show a 

 very significant correlation with annual egg production. 



In general, the data on clutch size indicate that intensity of laying is intimately 

 correlated with annual production. The importance of high intensity increases 

 as the laying year advances to summer, so that rate of laying is more important 

 in summer than at any other time of year. 



Pause 



8. Relation of Winter Pause Duration to Annual Production 



Winter pause as used in these studies represents a cessation in egg production 

 of eight or more successive days between November first and March first of the 

 pullet laying year. The causes of winter pause are known to be both genetic and 

 environmental. In this experiment attempts have been made to keep environ- 

 mental conditions as constant as possible but unsatisfactory la3ang houses limited 

 the possibilities. The duration of pause was tabulated against the annual produc- 

 tion, using only birds exhibiting pause, and gave the following constants: 



Number of birds with winter pause 721 



Mean winter pause — -days 36.47 



Winter pause standard deviation ±19.90 



Mean annual production — eggs 196.73 



Annual production standard deviation ±40.06 



Coefficient of correlation —.2565 ±.0235 



In the total population, 721 birds, or 49 percent, exhibited winter pause. 

 The duration of the pause was extremely variable, with a mean of about 36 days. 

 Mean egg production was relatively low for the pause birds — about 33 eggs 

 below that of the non-pause group. Regression was linear, and a significant 

 negative correlation appears between pause duration and annual production. 



9. Relation of Spring Pause Duration to Annual Production 



Pauses of eight or more days during March, April, and May may be classified 

 as spring pauses. They have been little studied, probably because most hens lay 

 particularly well at this time. In this population 356 hens exhibited a spring 

 pause. These have been tabulated to discover the correlation between spring 

 pause duration and annual production. The following values appeared: 



