Dr. Hansen has conducted basic and applied research to formulate new concepts regarding the nature of the interaction between the maternal system and developing embryo that have resulted in technologies to improve fertility of the female. Dr. Hansen developed a solution to the problem of infertility induced by heat stress through the use of embryo transfer. Research on the role of colony stimulating factor 2 (CSF2) as a maternal molecule that regulates embryonic development (termed embryokines) has revealed how molecules produced by the reproductive tract can regulate embryonic development to increase embryo competence to establish pregnancy and alter postnatal phenotype of the resultant o spring. His genetic research has identified new genes that confer thermotolerance to dairy cattle and has contributed to industry wide-efforts to improve the reliability of estimates of breeding value for reproductive traits.