Porcine reproductive and respiratory syndrome (PRRS) virus imposes devastating effects on swine health and productivity. Vaccination of animals is one way to reduce losses from infectious diseases including PRRS. Current modified live and killed vaccines have some success, although differentiation between vaccinated and infected animals has been a problem. In addition, live attenuated vaccines have resulted in appearance of PRRS like symptoms in sow herds and altering semen quality of boars. As such, new approaches are being utilized to develop better PRRS vaccine. Using harmless porcine adenovirus 3, we have constructed recombinant porcine adenovirus 3 expressing vaccine antigen genes (synthesized in the laboratory for increased expression) of PRRS virus. Although use of synthetic (codon optimized) PRRS virus glycoprotein genes helped to increase the level of expression of these glycoproteins in mammalian cells, it was not sufficient to induce a protective immune response in pigs.