fourty beef cows (330 kg) were allotted to a completely randomized design, in a 2x2 factorial scheme (two supplementation levesl [0.5 and 1.0% lw] and two energy sources [whole oat grain and ground corn grain]) to evaluate perfomance of animal grazing marandugrass (brachiaria brizantha hochst ex. a. rich stapf), during the dry season. supplements were formulated to contain 15% of crude protein (cp). average daily gain showed no difference among treatments (0.58 and 0.69 kg/d for oat, and 0.54 and 0.66 kg/d for corn, at levels of 0.5 and 1.0% lw, respectively). no difference was detected for carcass dressing among treatments, with average value of 46.12%. forage mass available was high, but quality was low, mainly as result of frost occurred in the period. average values for cp, neutral detergent fiber (ndf) and acid detergent fiber (adf) were 5.34, 74.95 and 47.66%, respectively. oat grain showed similar quality as corn for beef cow supplementation. considering high forage mass in the pasture, 0.5% lw supplementation showed higher economical efficiency.