Divergent Selection for Decrease and Increase in Egg Weight and Age of Sexual Maturity in Japanese Quail

The first experiment was designed to determine the effect of divergent selection for increase (HEW) and decrease in egg weight (LEW) in Japanese quail during three generations. These lines were established previously during two generations of divergent selection for increase and decrease in egg weight. A random bred group was also used as control group (C) that was established during three generations of random selection. After third generation selection, direct responses to selection for egg weight were 0.39 and -0.48 g in HEW and LEW lines, respectively. Also realized heritability of HEW and LEW lines were 0.30 and 0.28, respectively. There was a positive correlation between egg weight and4-wk BW in both lines (P<0.001). In the second experiment, two lines were selected for decrease (LMA) and increase (HMA) age at sexual maturity during generation 4 to 7. After four generations of individual phenotypic selection, direct responses to selection for age at sexual maturity were low. These values were –1.21 and 2.39 days for LMA and HMA lines, respectively. Realized heritability estimates of age at sexual maturity were greater in HMA (0.16) than LMA line (0.10). There was a negative correlation between age at sexual maturity and 4-wk BW in both divergent lines. BW at 4 weeks was positively correlated with BW at sexual maturity in both lines with the exception of the HMA line in the fourth generation. Age at sexual maturity and BW at the same time were positively correlated(P< 0.001) in generations 4 and 6 in the LMA and generation 6 in the HMA line.