A genome scan for QTL influencing milk production and health traits in dairy cattle

A genome scan was conducted in the North American Holstein-Friesian populat ion for quantitative trait loci (QTL) affecting production and health trait s using the granddaughter design. Resource families consisted of 1,068 sons of eight elite sires. Genome coverage was estimated to be 2,551 cM (85%) f or 174 genotyped markers. Each marker was tested for effects on milk yield, fat yield, protein yield, fat percentage, protein percentage, somatic cell score, and productive herd life using analysis of variance. Joint analysis of all families identified marker effects on 11 chromosomes that exceeded the genomewide, suggestive, or nominal significance threshold for QTL effec ts. Large marker effects on fat percentage were found on chromosomes 3 and 14, and multimarker regression analysis was used to refine the position of these QTL. Half-sibling families from Israeli Holstein dairy herds were use d in a daughter design to confirm the presence of the QTL for fat percentag e on chromosome 14. The QTL identified in this study may be useful for mark er-assisted selection and for selection of a refined set of candidate genes affecting these traits.