Breeding and Genetics: Molecular Genetics, QTL Detection and Marker Assisted Selection

Putative quantitative trait loci (QTL) affecting conformation traits in Holsteins have been detected using genotypic data generated by two research groups. Each research group conducted an independent genome scan in a select group of Holstein grandsire families. Six families were used by both groups and genotyped for 367 microsatellite markers in order to identify QTL affecting milk production and health traits. The same merged dataset has now been reanalyzed to identify putative QTL affecting conformation traits. Seventeen linear traits and four composite index traits were included in the analysis. The phenotypes were obtained from the Holstein Association USA (http://www.holsteinusa.com) and included standardized transmitting abilities for body type, feet and legs, and udder traits. Data were analyzed using QTL Express (http://qtl.cap.ed.ac.uk), a web-based regression interval mapping method. Preliminary analysis had identified 34 putative QTL affecting the conformation traits within the grandsire families. These QTL were significant at the chromosome-wise level (Fstatistic > 15) and were located on 15 bovine autosomes. Additional analysis is underway to determine which of these QTL, if any, are significant at the genome-wise level.