The oxidative stability of meat depends upon a combination of pro-and antioxidants and the degree of unsaturation of its lipid classes. When animals graze grass the concentrations of α-tocopherol and β-carotene in meat and fat increase and decrease when they are fed concentrates. Supplementation with α-tocopherol acetate increased αtocopherol concentration in the meat of concentrate-fed animals, less so for grass-grazed animals (Descalzo et al., 2005; Realini et al., 2004). Less is known about the relationship between diet, antioxidant enzymes systems such as Superoxide dismutase (SOD) and Catalase (CAT), and the oxidative stability of meat. This study aimed to determine the influence of a forage versus a concentrate diet fed to beef cattle, and an additional treatment with a PUFA-rich lucerne-based plant extract (PX), on the antioxidant profile of their meat, and its relationship with lipid oxidation and colour shelf life. The addition of PX raised the unsaturated nature of the beef muscle lipids and thus increased the oxidative stress (Kim et al., 2009).