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Individual phenotypic selection for high 4 week body weight was conducted for 40 generations in two lines of Japanese quail under two protein environments. Line P was selected on an adequate 28% protein diet, and line T was selected on a 20% protein diet containing 0.2% thiouracil (TU). In generation 20, a subline R was established by subjecting progeny from the T line to a 20% protein diet; in generation 27, a subline S was developed by subjecting progeny from the T line to a 28% protein diet containing 0.2% TU. Progeny from a nonselected control line (C) were reared with selected lines and sublines in all generations.Quail in the P line continued to respond to selection for 40 generations; body weights increased from 90 to approximately 200 g. Mean body weights of T line quail peaked in generation 22 and did not appear to show any definite gains thereafter. Body weight responses of sublines R and S were greater than those in the T line and indicate that changing the selection environment following long-term selection may be an effective technique to maximize total selection responses for 4-week body weight in quail. Realized heritability estimates for 4-week body weight were larger in the P line than in the T line in all comparisons. Realized estimates were high (30-45%) for the ten generations 1-10; moderate (15-20%) for generations 11-30, and small (5-10%) for generations 31-40. |
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