Most traits and disorders in animals, plants and humans have a multi-factorial rather than monogenic background. An improved understanding of the genetic regulation of these traits is important to facilitate development of more efficient strategies to manage a wide range of important health, welfare and ecological hazards. Examples of promising applications include personalized medicine, where diagnosis and treatment regimes of disease are guided by knowledge of an individuals genotype, and genomic selection to develop hardy and efficient breeds and varieties of animals and plants for a more sustainable agricultural production that require less input of antibiotics, pesticides and fertilizers in the production. Despite considerable efforts to understand the regulation of these traits, we still only have a superficial knowledge about the genetic mechanisms contributing to their expression. This research project use large scale genomic analysis in domestic animals to approach one of the grand challenges for the future: to decipher the genetic architecture of multi-factorial traits.