LENGTH OF BIOLOGICAL LAYING YEAR 7 



1. Relation of Length of Biological Year to First- and Second-Year Hatchability. 



The mean hatchability of the three persistency classes during the first and second 

 laying years is shown in ral)le L The data do not show any relation between 

 duration of biological year and percentage of fertile eggs hatched during the period 

 from March 25 to May 15 of each year. Hatchability therefore seems to be in- 

 dependent of those factors concerned with the duration of the laying year. The 

 data do indicate, however, that in general the same individuals have a higher 

 hatching reconl as yearlings than as pullets. 



2. Relation of Length ofBiologial Year to Body Weight at First Egg. 



Body weight at first egg is a measurement that may be taken at the beginning 

 of the bird's productive period. The value of such a record as a criterion of later 

 fecundity traits needs to be determined. Body weight of each of the 426 birds was 

 recorded on the day she laid her first pullet egg, and the mean for each of the three 

 persistency classes is shown in Table 1. These data indicate that greater duration 

 of the biological laying year is associated with a smaller body weight at first egg. 

 This smaller bod}' weight at first egg has been shown by Hays (1933) to be an ex- 

 plicit function of age at first egg. 



3. Relotioji of Lengtii of Biological ]'e(ir to Body Weight at the Close of the Pallet 

 ] ear. 



Only a part of the 426 birds considered in sections 2 and 3 were weighed at the 

 close of their laying year, the number being 96. These meager data are presented 

 (Table 1) to furnish a small amount of information on the relation between body 

 weight at the close of the 365-day laying year and duration of biological year. 

 These weight records were taken on a date averaging 365 days after the first 

 pullet egg for the birds housed together. 



The data suggest that birds with heavy weight at the close of their 365-day 

 production year are more likely to continue to lay than are smaller individuals. 

 In other words, birds that lay at the expense of body weight are likely to lay 

 fewer eggs as Hays (1932) pointed out, and they are also likely to have a shorter 

 producti\'e >'ear. 



4. Relation of Length of Biological ]'eay to Second- Year Egg Production. 



In the Rhode Island Red flock of the Massachusetts Agricultural Experiment 

 Station, the mean second-year production amounts to about 70 per cent of the first- 

 year production. Second-year records on this fiock are begun immediatehat the 

 conclusion of the 365-day record. By this system of records the second-year 

 record of a bird with a biological year of 365 days or more is penalized, in that all 

 of the non-producti\'e period usually accompanying molt falls in the second la\'ing 

 year. On the other hand, individuals with a short biological year show a part 

 of the molt period at the close of the 365-day first-year record and a part in the 

 beginning of the second-year record. The fact should also be noted that late 

 molting reduces the length of the molt period as Hays and Sanborn (1930) and 

 Marble (1930) have pointed out. 



The second-year egg records of the 426 birds studied are shown in Table 1. 

 The differences in mean annual egg records are not great for the three grouj^s. 

 In general, the data indicate that great length of the first biological year is likely to 

 be followed by a higher second-year egg record than might be anticipated if the 

 duration of the first biological year falls below 365 days. 



