DETECTION OF LOCI AFFECTING MILK-PRODUCTION AND HEALTH TRAITS IN AN ELITE US HOLSTEIN POPULATION USING MICROSATELLITE MARKERS

Quantitative trait loci (QTL) affecting health and milk production tra its were studied in seven large half-sib US Holstein families by using the granddaughter design. Genotyping for 16 markers was completed and marker allele differences within and pooled-across families were anal ysed. Potential QTL were identified for somatic cell score (SCS), fat yield, fat percentage, protein yield and protein percentage. Three mar kers (BM203, BM4505 and BM2078) were associated with significant effec ts for different traits and, after further analysis, may be useful in marker-assisted selection in specific families. Comparisons between th ese data and previously identified QTL support the location of a QTL f or milk yield and protein yield on chromosome 21.