NET CORRELATIONS OF CHARACTERS CONCERNED 

 IN FECUNDITY 



By F. A. Hays and Ruby Sanborn 



Annual egg })roduction has been found by several workers to depend upon 

 the characteristics early sexual maturity, non-pause, high intensity, non-broodi- 

 ness, and high persistency. All five of these traits have been shown to be 

 inherited in Mendelian fashion (Hays, 1924 and 1927). In order to obtain 

 niaxiinuin annual egg yield in the domestic hen, a combination of the above 

 five characteristics in the same individual is necessary, as well as very favor- 

 able environmental conditions. Familiarity with the mode of inheritance of 

 any one of the above five traits clearly indicates the difficulties in combining 

 all in the same individual and serves to explain the marked variability occur- 

 ring in the egg production of individual hens in the same flock. Even when 

 hens that carry all five of the desirable traits are used as brseders, there will 

 not be marked uniformity in production of the daughters of such matings 

 unless the breeding hens are genetically homozygous for the fecundity char- 

 acteristics and are mated to males of like genetic composition. Too much 

 stress cannot be laid upon the importance of selecting as breeders both males 

 and females that are homozygous for the characteristics sought. 



In previous reports (Technical Bulletins 7, 8, 9, and 11 of the Massachusetts 

 Agricultural Experiment Station), the relation of the five fecundity traits to 

 production has been fully considered by means of the simple coefficient of 

 correlation and the relative importance of each trait as a selection unit has 

 been studied. There yet remains to be considered in this concluding report 

 the net relation of each of the five traits to each other as well as to annual pro- 

 duction when all characteristics except the two under consideration are made 

 constant. These results are obtained by use of partial correlation coefficients 

 as calculated by standard formulae from the simple correlation coefficients. 

 For illustration: in calculating the partial correlation between age at first egg 

 and annual production; winter pause, intensity, broodiness, and persistency 

 are made constant. The use of partial correlation coefficients here accom- 

 plishes a two-fold purpose. First, it brings out any possible linkage between 

 traits — an invaluable item of information to the breeder. Second, it shows 

 clearly the relative importance of the five characteristics to fecundity so that 

 each may be properly stressed in the breeding program. 



The concluding section makes use of multiple correlation to discover the 

 exact degree in which annual production depends on the combined influence 

 of the five traits under consideration, and also whether other factors are con- 

 cerned in fecundity. 



Birds Used 



All of these studies are based on pullet-year records on Rhode Island Reds 

 bred by the Massachusetts Agricultural Experiment Station from 1916 to 1925. 

 The major portion of the birds was bred for fecundity, but each year there 

 has been included a limited number bred for broodiness and in inbreeding 

 studies. 



