There are numerous high quality peer reviewed research articles that confirm the health benefits of grass fed animals vs. grain fed animals. Here is an all-encompassing study from California State University that we enjoy referencing:
C.A.Daley, K.Harrison, P. Doyle, A. Abbott . (2010.) A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef. Nutrition Journal, 9:10.