Marker-assisted preselection of young dairy sires prior to progeny-testing

This study investigates the value of a 'bottom-up' approach to marker-assisted selection in a conventional progeny-testing dairy-breeding programme. By marker genotyping the daughters in the progeny test for markers known to be closely linked to a quantitative trait locus (QTL), it can be decided whether their sire is heterozygous for the QTL. If the sire is heterozygous with allelic contrast greater than some threshold, c, then only those bull-sons which inherited the favourable QTL allele are retained for subsequent progeny testing. In this way, posterior information on a sire's genotype from his daughters is used to preselect his sons and thereby increase the selection differential in the new generation of bulls. Simulations were used to predict the genetic gains and costs of using the bottom-up approach in a national dairy breeding scheme in which 500 young bulls were progeny-tested each generation. It was found that rates of genetic gains could be increased by 8%, 14% and 23% compared with conventional progeny testing if selection was based on 1, 2 and 5 QTL, respectively, and that this would cost less than US$100,000 per locus. A 'top-down' approach selecting QTL alleles inherited from the grandsires was also evaluated and shown to be highly profitable, though less so than for the bottom-up scheme. (C) 1998 Elsevier Science B.V. All rights reserved.