Abstract
Heritabilities and genetic correlations in some economically important characters were estimated and an attempt was made to construct an index which could be used under our farm conditions in Japan.
Heritabilities of rates of egg production were estimated to be 0.31, 0.17 and 0.15 for winter rate (P1), spring rate (P2) and total rate (P3) respectively, They were also estimated to be 0.48, 0.43, 0.46 and 0.49 for sexual maturity (S), body weight at sexual maturity (W1), body weight at approximately 300 days of age (W2) and egg weight at sexual maturity (EW), respectively.
Genetic correlations between P1 and P2, P1 and P3, and P2 and P3, were 0.187, 0.638 aed 0.701 respectively for production characters. They were estimated to be -0.210, 0.003 and 0.173 for SP1, SW2 and P1W2, respectively.
An index which could be applied under our farming conditions was proposed as follows:
I=1.40X2-X1+25.873X3
Where the subscripts 1 to 3 refer to sexual maturity, winter rate and body weight at 300 days. The economic weights assigned to the above three characters were -2, 5 and -1 respectively. The index is correlated 0.705 with the aggregate genotypic value of the birds.
Expected genetic changes in the means of the population selected on different criteria of selection were compared. It is evident that the efficiency of selection based on the index would be greater than selecting for any one of the characters involved in this study.
