Hazel L N, Dickerson G E, Freeman A E
Agricultural Research Service, University of Nebraska, Lincoln 68583-0908.
J Dairy Sci. 1994 Oct;77(10):3236-51. doi: 10.3168/jds.S0022-0302(94)77265-9.
When improvement is desired for several traits that may differ in variability, heritability, economic importance, and in the correlation among their phenotypes and genotypes, simultaneous multiple-trait index selection was more effective than independent culling levels or sequential selection. Such comparisons required definition of aggregate breeding value determined jointly by breeding values and economic importance of the component traits. The economic weight should approximate the partial regression of cost per unit of enterprise output value on breeding value for each trait. These can vary with production and marketing system, with performance of traits, and with breed role (i.e., paternal, maternal, or general) in crossbreeding systems. Genetic gains desired to maintain competitive ranking also may define the relative importance of traits. Because information available to estimate breeding values varies among the ages and categories of individuals under selection and because means are unknown, regressed (BLUP) predictions of trait breeding values are useful. They allow appropriate economic weights to be applied as the last step for predicting aggregate breeding values for individuals of different age classes, and they simplify choosing the proportions of selected breeders from each age class that maximize rate of change in aggregate breeding values. Inappropriate economic weights or errors in the parameters used to predict trait breeding values overestimate realized response in true aggregate breeding value.
当希望对几个在变异性、遗传力、经济重要性以及它们的表型和基因型之间的相关性方面可能存在差异的性状进行改良时，同时多性状指数选择比独立淘汰水平或顺序选择更有效。这种比较需要定义由组成性状的育种值和经济重要性共同决定的综合育种值。经济权重应近似于企业单位产值成本对每个性状育种值的偏回归。这些权重会因生产和销售系统、性状表现以及杂交系统中的品种角色（即父本、母本或通用）而有所不同。为保持竞争排名而期望获得的遗传进展也可能决定性状的相对重要性。由于用于估计育种值的可用信息在被选择个体的年龄和类别之间存在差异，并且均值未知，因此性状育种值的回归（最佳线性无偏预测，BLUP）预测很有用。它们允许在预测不同年龄类个体的综合育种值的最后一步应用适当的经济权重，并且简化了从每个年龄类中选择种畜的比例，以使综合育种值的变化率最大化。不适当的经济权重或用于预测性状育种值的参数中的误差会高估真实综合育种值中的实际反应。
