Divergent selection for body weight and yolk precursor in Coturnix coturnix japonica. 7. Influence of genetic changes in body weight and yolk precursor on egg production.

Japanese quail lines were started from a randombred control by selecting for high (HW) or low (LW) 4-week body weight and high (HP) or low (LP) total plasma phosphorus (P), a measure of yolk precursor. In the 9th generation, 2 sublines were initiated from Line HW based on high (HW-HP) or low (HW-LP) level of P in females while males were continually selected for HW. A subline (LP-HW) was started from Line LP in the 9th generation by selecting the males for HW while continuing to select the females for LP. All lines were maintained with 36 parental pairs. Realized heritability (h2) values for 4-week body weight were .38 +/- .02 in Line HW and .32 +/- -.02 in Line LW for 15 generations. Respective h2 were .32 +/- .01 and .34 +/- .01 for P in Lines HP and LP. Although P increased in Line LW, there was no change in Line HW. Body weight of Lines HP and LP declined slightly, but significantly. Egg production decreased significantly in Lines HW, LW, HP, HW-HP, and LP-HW, but did not change in Lines LP and HW-LP. Decrease in egg production of Line HW-HP was greater than that of Lines HW or HP. These results suggest that if both body weight and P are selected for simultaneously, then egg production will decrease more than if selection pressure is applied on either trait alone, even though the two traits do not appear to be genetically closely correlated.