The invention relates to improved methods to integrate heterologous DNA into the genome of non-human animals. The transgenic constructs contain a site recognized by a site specific recombinase which can be used to catalyze the insertion of the transgene into the animal's genome. The transgenic constructs and site specific recombinase are introduced into oocytes using sperm. Fertilized oocytes are maintained under conditions that allow recombinase-mediated integration of the transgene into the genome of the non-human animal and development to term. Transgenic animals with transgenes integrated by a recombinase express transgenes at higher levels compared to transgenic animals with randomly integrated transgenes.