Live weight gain (LWG) and meat fatty acid composition (FA) were evaluated in Hereford steers fed on pasture with or without oat grain. The study site was non-traditional pastures were used in the dryland Andes foothills, VIII Region, Chile (36° 49' S, 71° 55' W), including forages such as alfalfa (Medicago sativa), orchard grass (Dactylis glomerata) and roadside brome (Bromus stamineus). Ten calves with an average LW of 173 kg were fed with red clover (Trifolium pretense L. var. Quiñequeli) during winter. In spring, 50% of steers were fed only pasture (P), and the other half were fed the same pasture in rotational grazing supplemented with oat grain (PO), 2.5 kg steer-1 day-1. The LWG was 0.78 and 0.91 kg day-¹ for the P and PO treatments, respectively. The animals of both treatments reached an average of 380 kg LW at 16.5 months of age. FA composition of beef was different in tenderloin and round, with and without oat grain supplement and in roasted and raw meat. The cholesterol content did not present differences. The linoleic AG (C18:2 n-6) / linolenic AG (C18:3 n-3) ratio in meat was 2.0:1 and 2.45:1 for P and PO, respectively.