Detection of putative loci affecting milk production and composition, health, and type traits in a United States Holstein population

Quantitative trait loci affecting milk yield and composition, health, and t ype traits were studied for seven large grandsire families of US Holstein u sing the granddaughter design. The families were genotyped at 20 microsatel lite markers on 15 chromosomes, and the effects of the marker alleles were analyzed for 28 traits (21 type traits, 5 milk yield and composition traits , somatic cell score, and productive herd life). Markers BM415 on chromosom e 6 and BM6425 on chromosome 14 were associated with effects on protein per centage in a single grandsire family. The latter marker had a lower probabi lity of being associated with changes in milk yield and fat percentage is t he same-family. Increases in productive herd life were associated with an a llele at marker BM719 on chromosome 16 in one grandsire family.