Association of growth hormone loci with milk yield traits in Holstein bulls

A pedigree analysis was used to investigate the association of bovine growt h hormone loci with milk production traits of Holstein cattle. Holstein bul ls were typed for three bovine growth hormone loci located in exon V, intro n C, and the 3' region of the gene. Phenotypic data were daughter yield dev iations for milk, fat, and protein yields and for fat and protein percentag es. Analysis of linkage across families was applied to the data using one o r two bovine growth hormone loci as markers linked to a putative biallelic quantitative trait locus. Estimated parameters were allele frequency, genot ypic means, within-genotype standard deviation of a putative quantitative t rait locus, and recombination fraction between the markers and the quantita tive trait locus. Parameters were estimated by maximum likelihood technique s. The estimated frequency of the quantitative trait locus allele that decr eased the value of the phenotype ranged from 0.1 for milk yield to 0.6 for protein yield. The estimated effect of an allele substitution at the quanti tative trait locus, given in phenotypic standard deviation units, ranged fr om 0.75 for fat percentage to 1.6 for milk yield. The standard deviation wi thin genotype ranged from 0.67 for fat yield to 0.87 for milk yield. The es timated recombination fraction was close to zero for protein percentage, in dicating physical linkage between a quantitative trait locus affecting the trait and the bovine growth hormone loci.