FACTORS AFFECTING ANNUAL EGG PRODUCTION 

 By F. A. Hays and Ruby Sanborn 



INTRODUCTION 



Goodale (1918) first pointed out that annual egg production was dependent 

 upon a considerable number of characters and stated that selective breeding 

 should be based on this principle rather than upon gross annual egg records. 

 Hays (1924) showed that a number of these characters were defiruitely inherited. 



During the last 25 years the methods of poultry breeding have been greatly 

 modified and improved so that the modern breeder selects and establishes specific 

 characters that are known to affect annual egg production. The extensive 

 literature concerned with modern poultry breeding is not reviewed here since 

 this has been well done in the latest books on poultry breeding. Reference is 

 made only to work having a particular bearing on the subject considered. 



Character of Birds Used 



The birds included in this study were all Rhode Island Reds that had been 

 bred for many years for characters affecting egg production. The data were 

 obtained from the first-year records of six generations of females hatched from 

 1937 to 1942 and included a total of 1470 birds. Only individuals with apparently 

 normal annual trapnest records were included. This is the same population 

 that was reported on in Bulletin 416 (Hays, 1944). 



Object of Investigation 



The study had one primary objective, which was to discover as many characters 

 as possible that might aflfect annual egg production. The value of such informa- 

 tion to the breeder lies in his ability to use such characters as units of selection 

 in making up breeding pens. 



The coefficient of correlation is probably the best measure of association where 

 large samples are used. In this study the simple correlation was determined be- 

 tween sixteen independent variables, with the annual egg record as the dependent 

 variable in all cases. The Blakeman test for linearity of regression was also 

 applied. 



RESULTS OF INVESTIGATION 



Hatching Date 



1. Relation of Hatching Date to Annual Production 



Hatching dates ranged from March 6 to April 30 in the six-year period. During 

 the first two years there were eight weekly hatches; in the next three years, seven 

 weekly hatches; and in 1942, six weekly hatches. Annual egg records in all cases 

 cover a period of 365 days beginning on the date the first pullet egg was laid. 

 The simple correlation was detennlned between the hatching date and annual 

 egg production, giving the following constants: 



Number of birds 1470 



Mean hatching date April 1 



Hatching date standard deviation — weeks. ... ±1.87 



Mean annual production — eggs 213.57 



Annual production standard deviation +43.38 



Coefficient of correlation -|-.0412 ±.0176 



