Detection of quantitative trait loci affecting milk production traits on 10 chromosomes in Holstein cattle

Sons (n = 71 to 75) of each of six Holstein sires were genotyped at 69 micr osatellite loci covering a total of 676 cM on chromosomes 3, 5, 9, 10, 13, 15, 17, 20, 23, and 26. Estimates of quantitative trait loci (QTL) effect a nd location were made using a least squares interval mapping approach based on daughter yield deviations of sons for 305 d milk, fat, and protein yiel d and fat and protein percentage. Thresholds for statistical significance o f QTL effects were determined from interval mapping of 10,000 random permut ations of the data across the bull sire families and within each sire famil y separately, Analyses combining data across sires indicated the presence o f QTL affecting milk, fat, and protein yield on chromosomes 20 and 26 and a QTL affecting fat and protein percentage on chromosome 3. Analyses within each sire family separately indicated the presence of segregating QTL in at least one family on 7 of the 10 chromosomes. Statistically significant est imates of QTL effects on breeding value ranged from 438 to 658 kg of milk, from 17.4 to 24.9 kg of fat, 13.0 to 17.0 kg of protein, 0.04 to 0.17% fat, and 0.07 to 0.10% protein.