The aim of this work was to study the effects of grass utilization in the diets on performance of finishing Bísaro pigs. A total of 22 pigs (16 castrated males and 6 females) was housed outdoors and fed ad libitum (37-85 kg live weight) on a growing diet and then transferred to an indoor system (with free access to an outdoor area) for 49
days, according to 3 different treatments: 100% concentrate (C), 75% concentrate + ad libitum grass (CE75), 50% concentrate + ad libitum grass (CE50). The grass was supplied and its intake registered on a daily basis. Every 14 days, the pigs were weighted and their backfat (P2 in vivo) measured. After slaughter (average weight of 107 kg LW),
yield and 1/2 left carcass characteristics were controlled. During the outdoor growing phase, the ADG was 513 g/day. During the indoor finishing phase, the increase was proportional to the reduction of concentrate in the diet. The ADG(g) and the fat deposition (P2 cm) were significantly different (P