Genetic and clonal responses in closed dairy cattle nucleus schemes

Abstract

ABSTRACTThe additive genetic response per generation and the genetic superiority of female genotype(s) selected for commercial cloning (clonal response) were maximized for a closed adult nucleus scheme, with 256 or 1024 test places, by varying the mating design (number of clones, full-sibs and half-sibs). Responses were corrected for effects of finite sample size and correlated index values on the selection intensity, and variance reduction due to selection. Additive genetic responses, which varied from 0·153 to 0·514 phenotypic standard deviations per generation, were 0·68 to 0·89 of corresponding uncorrected predictions. Reductions were largest when the intensity and accuracy of male selection were high. Clonal responses varied from 0·460 to 2·506 phenotypic standard deviations, increasing with the intra-clone correlation, the intensity of clonal selection and the test capacity. Reductions in clonal responses, which varied from proportionally 0·04 to 0·27, were smallest when dominance variance was high. Increasing the test capacity resulted in a proportionally 0·21 to 1·55 increase in genetic responses, while proportional increases in clonal responses varied from 0·09 to 0·36. With selection of only one male per full-sib family, designs which maximized genetic and clonal responses were different in all cases. Differences were largest when the heritability and the intra-clone correlation were low and the intensity of clonal selection was high. Without the restriction on male selection, optimal mating designs were different, unless dominance variance and intensity of clonal selection were both low.