Research was conducted to evaluate nutritional effects on carcass traits, meat quality and fatty acid composition of beef, and the role of antioxidants in improving color and lipid stability. In experiment 1, thirty Hereford steers were finished either on grass (GRASS, n=10) or concentrates (CONC, n=20). Half of the CONC steers were supplemented with vitamin E (VITE), and postmortem vitamin C (VITC) was added to ground beef. GRASS carcasses had lower weight, conformation, fat depth and ribeye area as well as darker longissimus color and yellower fat than CONC. Initial Warner-Bratzler shear force was similar among treatments, but GRASS had lower values after 7 d postmortem. VITE supplementation of CONC increased lipid stability of ground beef and steaks, but was unable to improve color stability; whereas VITC increased color stability without altering lipid oxidation in ground beef. GRASS enhanced the unsaturated fatty acid (FA) profile of intramuscular fat in beef including conjugated linoleic acid (CLA) and omega-3 (n-3) FAs. In experiment 2, postmortem vitamin C (VITC) was added to ground beef from grass-fed (GRASS) or grain-fed (GRAIN) sources. Near infrared reflectance (NIR) spectroscopy was used to predict FA composition of ground beef and to discriminate samples from GRASS vs. GRAIN. VITC was effective in retarding pigment oxidation in ground beef from both GRAIN and GRASS; however, VITC reduced lipid oxidation in GRAIN samples only, despite higher concentrations of polyunsaturated FAs in GRASS. NIR can be used to predict accurately the content of total saturated and unsaturated, and stearic, oleic, and linolenic FAs in ground beef; and to discriminate meat samples from GRASS vs. GRAIN. In experiment 3, fourteen Hereford steers were finished on tall fescue infected with either wild-type (TOXIC; n = 6) or novel, non-toxic (MAXQ; n = 8) endophyte. Although MAXQ supports higher cattle performance than TOXIC, these results suggest that endophyte type has minimal effects on carcass traits, and meat quality of grass-fed beef. Toxicosis may influence FA metabolism and fat necrosis. Finishing cattle on tall fescue pastures showed potential to enhance the FA profile of intramuscular fat in beef including CLA and n-3 FA.