6 MASS. EXPP:R1MF.\T station RTLLETIX 208 



7. Relation Between Length of Biological Year and A nnualEgg Record. 



Annual egg record as used throughout this report covers the period from first 

 pullet egg to 364 days thereafter for each individual. It is highly desirable to 

 know whether the bird possessing the ability to lay continuously for more than a 

 year is more likely to be a heavier layer in the first 365 days of production. By 

 tabulating the length of the biological year and the annual egg record of each 

 individual, the following constants were obtained: 



Number of birds 911 



Mean biological year — days 363.62 



Biological year standard deviation ~r43.16 



Mean annual production — eggs 229.92 



Annual production standard deviation +32.72 



Coefiticient of correlation +.4715 + .0174 



Correlation ratio .5520+0155 



The regression of production on duration of biological year is found to be non- 

 linear by Blakeman's test: con.sequently the correlation ratio measures the associa- 

 tion between these two variables. The actual value of length of biological year 

 as a selection unit may be determined by squaring the correlation ratio which 

 gi\-es .3047. Stated simply, this means that 30 per cent of the variation in annual 

 production is due to variation in duration of biological year. 



In general, the data presented in Part 1 of this report indicate that the ability 

 to lay for a long period of time is desirable from the standpoint of egg production. 



Part 2. — Relation of Length of Biological Year to Some Important First - 

 and Second -Year Characteristics 



In this part consideration is given to several desirable characteristics not speci- 

 fically related to first-year egg production but very important in breeding for high 

 fecundity. Further evidence is presented to show whether or not a long biological 

 year may be considered of sufficient significance to take an important place in the 

 breeding program. The length of biological year is considered in relation to first- 

 and second-year hatchability, to body weight at first egg, to body weight at the 

 close of the pullet year, and to second-year egg production. 



In the generations used in this report there were 426 birds with complete two- 

 year records. This group was divided into three classes with respect to duration 

 of biological year; those with persistency of less than 315 days; those with per- 

 sistency ranging from 315 to ?<b^ days; and those with persistency exceeding 365 

 days. 



T.\BLE 1 — Relation of Length of Biological Laying Year to H.\tch- 

 ABiLiTY, Body Weight, and Second-Year Egg Production 



Length of Number Hatchability Body weight Second- 

 biological of per cent pounds year 



year birds egg 



First Second M At end of produc- 



year year first pullet tion 



egg year 



Under315days 26 67.60 72.50 5..S3 5.95(2)* 156.50 



From 315 to 365 days 159 78.30 78.21 5.44 5.89(25) 147.84 



Over 365 days 241 71.72 77.35 5.30 6.09(69) 160.91 



*Only a part of the 426 birds were weighed at the close of their laying year. The figures in paren- 

 thesis show the number of such birds in each class. 



