MAPPING QUANTITATIVE TRAIT LOCI CONTROLLING MILK-PRODUCTION IN DAIRY-CATTLE BY EXPLOITING PROGENY TESTING

We have exploited ''progeny testing'' to map quantitative trait loci ( QTL) underlying the genetic variation of milk production in a selected dairy cattle population. A total of 1,518 sires, with progeny tests b ased on the milking performances of >150,000 daughters jointly, was ge notyped for 159 autosomal microsatellites bracketing 1645 centimorgan or approximately two thirds of the bovine genome. Using a maximum like lihood multilocus linkage analysis accounting for variance heterogenei ty of the phenotypes, we identified five chromosomes giving very stron g evidence (LOD score greater than or equal to 3) for the presence of a QTL controlling milk production: chromosomes 1, 6, 9, 10 and 20. The se findings demonstrate that loci with considerable effects on milk pr oduction are still segregating in highly selected populations and pave the way toward marker-assisted selection in dairy cattle breeding.