Selection for High and Low Yolk-albumen Ratio in Chickens:II. The Direct Responses to Selection on the Yolk-albumen Ratio for Seven Generations
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概要
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The experimental genetic improvement by artificial selection on egg quality traits as one of the breeding objectives for chickens has received little attention. Divergent selections for the high and low yolk-albumen ratios in chickens were carried out through seven generations to test the effects on various egg-component traits. The effect of selection on the yolk-albumen ratio was shown in this report.A random-bred base population of White Leghorns was classified into four groups according to egg weight (L, ML, MS and S). In each group, two lines were selected for the high and low yolk-albumen ratio. Four selected high lines were designated as LL, MLL, MSL and SL, and four selected low lines were designated LS, MLS, MSS and SS. A control line was also in this study.The results obtained were as follows:1) Through the process of generation studied, an increase in the yolk albumen ratio in selected high lines (2.84% to 7.50% against zero-generation), and a decrease in selected low lines (1.70% to 6.92%) were observed in the trends of direct response from the evaluated population means.2) The realized gains in selected high lines when adjusted to the control line were significantly higher than low lines. When the realized gains per generation in the selected high lines were estimated by the use of linear regression analyses, they were 2.145% (SL), 1.846% (MSL), 1.181% (MLL) and 1.767% (LL), and were statistically significant. In the selected low lines they were 0.087%, -0.455%, -0.170% and 0.213% in SS, MSS, MLS and LS, respectively.3) The responses to selection per generation as shown by the difference in gains between the selected high and low lines were 2.057%, 2.301%, 1.351% and 1.126% in SL-SS, MSL-MSS, MLL-MLS and LL-LS, respectively, and were highly significant.4) The average estimated heritability of the yolk-albumen ratio within generation, computed by full-sib correlations was 0.15 to 0.53 and by daughter-dam regressions was 0.55 to 1.22.5) The realized heritability of the yolk-albumen ratio, calculated from the regressions of realized gains on the cumulative selection differentials, was 0.29 to 0.50 in the selected high lines, and was 0.01 to 0.08 in the low lines. Based on the differences of responses between the selected high and low lines, the realized heritability was 0.28, 0.28, 0.18 and 0.16 in SL-SS, MSL-MSS, MLL-MLS and LL-LS, respectively.6) In every case, the direct responses to high and low selection for the yolk-albumen ratio were markedly asymmetrical, due to the slight responses in selected low lines. However, significant differences in the expected and realized selection differentials were not observed among the selected high and low lines. Also, the effects of inbreeding and male genotypes were not recognized in the asymmetrical direct responses.
- 日本家禽学会の論文
日本家禽学会 | 論文
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