Long-Term Selection for Four-Week Body Weight in Japanese Quail Following Modification of the Selection Environment

The effect of changing the selection environment to maximize long-term genetic improvement in growth was investigated in a selection study for high 4-wk body weight in Japanese quail. This investigation involved three selected lines: Line P, selected under a 28% protein diet; Line T, selected under a 20% protein diet containing .2% thiouracil (TU), and Line S, a subline taken from the T line in Generation 27 and thereafter selected under a 28% protein diet containing TU. From Generations 27 to 70, 4-wk body weights increased 31%, 40%, and 51% in the T, P, and S lines, respectively. Selection differentials and intensities were significantly lower in the S line than in the P and T lines. Realized heritabilities calculated by dividing the cumulative response by the cumulative selection differential across the 43 generations were .05, .10, and .14 in the T, P, and S lines, respectively. These data indicate that changing selection environments may result in the release of additional additive genetic variation and thereby have a favorable effect on long-term genetic gains in body weight.