LENGTH OF BIOLOGICAL LAYING YEAR 5 



5. Relation Behveeii A initial Persistency a iid 365- Day Egg Record. 



The correlation between annual persistency within a 365-clay period from lirst 

 pullet egg and the 365-day egg record has been shown to be intimate in the genera- 

 tions of birds hatched at the Massachusetts Station from 1916 to 1Q24 (Hays and 

 Sanborn, 1926). This study is repeated using the 911 ijirds considered in this 

 report. In the earlier report the authors pointed out that the birds were divided 

 into two genetic classes: namely, those laying for a shorter period than 315 days and 

 those laying for 315 days or longer before the annual molt. In this earlier report 

 and in this section the duration of egg production beyond the 365-day limit is not 

 considered. The fact should be noted in connection with these correlation studies 

 that the birds used represent a selected group that was kept for two laying years 

 because of superior pullet-year records. The following constants were derived 

 from the correlation table: 



Number of birds 911 



Mean annual persistency — days 34-2.11 



Annual persistency standard deviation +33.98 



Mean annual production — eggs 229.92 



Annual production standard de\'iation +32.72 



Coefficient of correlation +.579S+.014.S 



Correlation ratio .6257 +.0136 



The relation between annual persistency and annual egg production proved not 

 to be linear by Blakeman's test. The correlation ratio shows in this population an 

 intimate association between persistency and production. Its squared value is 

 .3915 indicating that about 40 per cent of the variation in production is associated 

 with variation in persistency. As a unit in selection persistency is of great value. 



6. Relation Bet-ween Length of Biological Year and the Egg Record for the Biologi- 

 cal Year. 



It is desirable to know whether the egg record during the biological year is in- 

 timately associated with the duration of the biological year. In other words, is 

 there high probability that a long period of laying previous to molt is likely to be 

 associated with a high egg record? By tabulating each bird in a correlation for 

 length of biological year and egg production in the same period, the constants below 

 were obtained : 



Number of birds 911 



Mean biological year — days 363.62 



Biological year standard deviation +43.16 



Mean egg record for biological year 237.52 



Egg record standard deviation +38.57 



Coefficient of correlation +.6999 +.01 14 



Mean egg production during the biological year is 237.52 compared with 229.29 

 lor the 365-day year. The variability of production is also somewhat greater in 

 the biological year. The regression of egg production on duration of biological 

 year is found to be linear. The coefficient of correlation is highly significant and 

 by its squared value indicates that 48.99 per cent of the variation in egg record 

 for the biological year is due to variation in duration of the biological year. This 

 value is highly significant in biological flata and attai hes considerable importance 

 to the length of the biological year. 



