The speed congenic strains developed herein confirm previously identified genome-wide QTL affecting growth, obesity and carcass composition. Our novel congenic development approach on MMU2 provided confirmation of QTL-hg interactions, which will significantly aid in future fine mapping experiments. The identification of the molecular mediators of QTL-hg epistasis as well as the QTG for the remaining congenics will provide essential information on the molecular genetic architecture of growth and obesity.