LONG-TERM SELECTION FOR BODY-WEIGHT IN JAPANESE-QUAIL UNDER DIFFERENTENVIRONMENTS

Long-term selection was conducted for high 4-wk BW in Japanese quail u nder different selection environments to investigate selection limits and to determine whether genetic parameters for growth are similar to those in chickens. Quail lines were selected under an adequate 28% CP diet (P line) and under a low 20% CP diet (T line). Mean realized heri tabilities ranged from 0.32 (T line) to 0.49 (P line) during the first 10 generations. Although genetic variation remained following 97 gene rations of selection, realized heritabilities obtained agreed with the oretical predictions of loss of additive genetic variability with cont inuous selection. Similarity of heritability estimates indicates that Japanese quail are an excellent model for genetic studies of growth in meat-type chickens. Positive relationships accompanying selection for high 4-wk BW were increases in adult BW, age at first egg, and egg we ight. Negative relationships were decreases in percentage fertility an d hatchability, and egg production. Increased growth rate in selected lines was accompanied by an increase in feed and water intake, and by improvement in feed efficiency. Feed efficiency differences appeared t o be important only immediately following hatch, whereas feed intake d ifferences were present from 0 to 4 wk. Evidence of major physiologica l changes accompanying selection for growth were not observed. However , changes were observed in increased ''resource allocations'' to suppl y organs, during late embryonic stages and the Ist wk posthatch. Carca ss composition was similar between unselected and selected lines excep t for higher fat and lower moisture levels in selected lines.