Testing for the presence of previously identified QTL for milk production traits in new populations

Five chromosomal regions previously associated with milk production traits were tested in 16 families of Black and White cattle from the UK. The trait s were also linearly transformed into genetically and phenotypically indepe ndent variables normalized by phenotypic variances ('canonical traits'). Si gnificant associations with the untransformed and canonical traits were fou nd for bovine chromosome 6. There was also evidence that chromosome 9 influ enced these traits. The linear transformation clarified the effects of chro mosomal regions; regions with effects on all three untransformed traits (mi lk, fat and protein yields) were generally condensed into an effect on a si ngle canonical trait. Comparison of our results with those reported previou sly for American Holstein cattle suggested that the QTL may not be the same .