THE SIGNIFICANCE OF 



LENGTH OF BIOLOGICAL LAYING YEAR 



IN PRODUCTION BREEDING 



By F. A. Hays, Research Professor, and Ruby Sanborn, Research Assistant, 

 in Poultry Husbandry 



Introduction 



High persistency as incHcateti by late molting at the end of the pullet laying year 

 has long been recognized as very desirable from the standpoint of high annual egg 

 production. A review of the literature on this point scarcely seems necessary. 

 Suffice it to note that Hays and Sanborn (1927 c) report a net correlation of 

 + .7501 +.0063 between annual persistency and annual egg prorluction in Rhorle 

 Island Reds at the Massachusetts Agricultural Experiment Station. 



This report is concerned with the duration of the biological laying year; that is, 

 the period from first pullet egg to a 30-day cessation of production after March 1. 

 In those birds which did not stop laying for as long as 30 days after they had 

 passed the 365-day production date, the onset of a pause of 8 or more days was 

 considered as the termination of the biological year. In the 12 generations studied 

 there were 1 1 individuals that showed no cessation of production as great as 8 days 

 at the close of the pullet year, and these were omitterl. 



The studies reported below were undertaken to discover whether birds that con- 

 tinue to lay without interruption for 13, 14, or 15 months are actually superior for 

 breeding purposes to birds laying for 9 to 12 months before molting. The report 

 is divided into three parts: (1) Correlation studies showing the relation of length 

 of biological year to characters affecting fecundity and to egg production; (2) The 

 relation between the length of the biological year and other desirable characteris- 

 tics; and (3) The relation between the duration of the biological year in mothers 

 and annual persistency and production of their daughters. 



Birds Used for the Study 



All birds used were Rhode Island Reds from the Station flock that has been 

 developed since 1913, and include females hatched in the non-broody line, the high- 

 production line, the hatchability experiment, the experiment on variability in 

 production, the experiment on egg .size and egg character, and the studies on the 

 relation of intensity to feather color. Twelve generations, hatched in 1917 and 

 from 1920 to 1930 inclusive, were used in Parts 1 and 2. The twelve generations 

 of daughters reported in Part 3 were hatched in 1918 and from 1921 to 1931 in- 

 clusive. Two generations were omitted in both cases because the birds were dis- 

 carded without complete records on account of disease epidemics. Only birds 

 retained for two full laying years are included in Parts 1 and 2. 



Part 1. Correlation Studies 



The relation of the length of biological laying year to some important inherited 

 characters known to affect egg laying is considered, as well as the relation of length 

 of the biological year to the egg record made during the biological year and the 

 annual egg record. The coefficient of correlation was used to measure the associa- 

 tion by tabulating each bird with respect to the two characters being considered. 

 Kach correlation was tested for linearity by Blakeman's (1905) test. In those 



