| A genome scan for quantitative trait loci (QTLs) influencing milk production, health and conformation traits was completed in Holstein-Friesian cattle using a granddaughter design. Eight half-sibling families consisting of 1,068 bulls were genotyped for 174 microsatellite markers. The markers provide coverage of 2,500 cM or approximately 85% of the cattle genome. Quantitative trait loci with genomewide significance were identified for effects on milk fat percentage (BTA3), milk fat yield and percentage (BTA14) and overall type composite (BTA5). Additional marker/QTL effects with suggestive significance were found for front teat placement, dairy composite and body depth on BTA1, milk protein percentage on BTA2 and BTA3, udder composite and front teat placement on BTA5, teat length on BTA6, dairy composite on BTA7, fore udder attachment on BTA10, feet and leg score on BTA11, milk protein yield on BTA21, and dairy form on BTA27. A multimarker regression analysis mapped the QTL for fat percentage to chromosome position 46 cM on BTA3 between the markers BL41 and TGLA263. On the basis of a radiation hybrid map, the QTL(s) map to the chromosomal interval bounded by the genes TSHB and EDG1. Positional and comparative positional candidate genes for the fat percentage QTL are CSF1, AMY2, GNAI3, VAV3 and STXBP3 . QTLs identified in this study may lead to improved genetic gains in dairy cattle through marker-assisted selection, therapeutics, or transgenics. |
