Divergent selection for body weight and yolk precursor in Coturnix coturnix japonica. 9. Evaluation of traits associated with onset of sexual maturity.

An experiment was conducted to compare traits associated with onset of sexual maturity in Japanese quail lines. Lines divergently selected for high and low 4-wk BW (HW and LW), and high and low total plasma phosphorus at beginning of lay (HP and LP) were compared with a randombred line (RBC1) that served as the base population for HW, LW, HP, and LP. The HW sublines (HW-HP and HW-LP) and LP subline (LP-HW) were also compared to their respective line of origin. Most of the differences observed for males selected for a single trait were found for weight-selected rather than for phosphorus-selected lines. The patterns of significance closely followed differences expected due to the extreme diversity in BW for the HW and LW when compared with RBC1. Females generally matured approximately 2 wk later than males for HW, HP, and LP. Line LW females matured approximately 4 wk later than LW males. Differences were observed for variables associated with onset of sexual maturity for HW, LW, and HP when compared with RBC1. Observed changes in carcass variables for sublines were generally associated with reductions in BW for HW-HP, and HW-LP versus HW and for increases in BW for LP-HW versus LP. The differences were likely due to the fact that two-trait selection (BW for males and total plasma phosphorus in females) has allowed weights to diverge when compared with lines selected for single traits.