A quantitative trait locus for live weight maps to bovine Chromosome 23

A multiple-marker mapping approach was used to search for quantitative trai t loci (QTLs) affecting production, health, and fertility traits in Finnish Ayrshire dairy cattle. As part of a whole-genome scan, altogether 469 bull s were genotyped for six microsatellite loci in 12 families on Chromosome ( Chr) 23. Both multiple-marker interval mapping with regression and maximum- likelihood methods were applied with a granddaughter design. Eighteen trait s, belonging to 11 trait groups, were included in the analysis. One QTL exc eeded experiment level and one QTL genome level significance thresholds. Ac ross-families analysis provided strong evidence (P-experiment = 0.0314) for a QTL affecting live weight. The QTL for live weight maps between markers BM1258 and BoLA DRBP1. A QTL significant at genome level (P-genome = 0.0087 ) was mapped for veterinary treatment, and the putative QTL probably affect s susceptibility to milk fever or ketosis. In addition, three traits exceed ed the chromosome 5% significance threshold: protein percentage of milk, ca lf mortality (sire), and milking speed. In within-family analyses, protein percentage was associated with markers in one family (LOD score = 4.5).