Quantifying the selection response using a residual feed intake DNA marker for two Australian breeding objectives

A pseudo-BLUP index was used to evaluate the selection response from using a quantitative trait locus (QTL) for residual feed intake (RFI). The index included phenotypic information on the individual, sire, dam, half-sibs and progeny. To compare with marker-assisted selection (MAS), a single locus was assumed to be genotyped that explained a proportion of the variance for RFI and this was included in the selection index. Two breeding objectives were examined with a different relative economic value for RFI, one targeting the Australian domestic market and one targeting a high value Japanese export market. The selection response and optimal age structure altered with the inclusion of genotype information, Response was increased because the pre-selection accuracy, before RFI measurement, was improved. Genotyping increased the earlier selection of sires and decreased the optimum generation interval of sires; consequently, this increased the annual selection response. With a QTL that explained 0.33 phenotypic standard deviations of variance, response was shown to increase by up to II % when both sexes were genotyped and 7.6% when only males were genotyped. When sire selection was delayed until after 2 years of age, the increase in response from genotyping was 8.1% and 5.1%, respectively. If the QTL explained a relatively large part of the breeding objective, the locus was rapidly fixed resulting in rapid early gains.