Fine Mapping of Quantitative Trait Loci on Bovine Chromosome 6 Affecting Calving Difficulty

Calving difficulty is an economically and ethically important trait for dairy cattle breeding. The aim of the present paper was to refine the position of a previously detected quantitative trait locus (QTL) affecting calving difficulty (direct effect) in Norwegian Red dairy cows. A granddaughter design consisting of 18 elite sire families and a total of 713 sons was genotyped for 154 markers spanning the QTL region, and the trait data were analyzed by using a combined linkage and linkage disequilibrium approach. A highly significant QTL was detected in a 150- kb interval between the markers LAP3_281 and BTA-114677. Additionally, there were some indications of a second QTL between the markers BTA-75776 and BTA-75780 located less than 500 kb apart. Several candidate genes may be identified close to these QTL. Of these, a cluster of genes expected to affect bone and cartilage formation may be of particular interest for follow-up studies.