Feeding Iberian pigs with acorns and grass in either free-range or confinement affects the carcass characteristics and fatty acids and tocopherols accumulation in Longissimus dorsi muscle and backfat

The experiment was undertaken to provide information on the influence of grass intake in a high fat diet based on acorns, in either free-range or confinement, on the carcass yield and characteristics, and on the accumulation of fatty acids and tocopherols. Groups raised free-range or with acorns and grass in confinement had the highest total backfat. Grass addition to the feed did not significantly modify the carcass weight and cut yield. However, outdoor raising produced lower carcass weights and yield, Longissimus dorsi muscle and ham weights than those fed the formulated diet or acorns and grass in confinement. Neither grass intake nor outdoor rearing did modify significantly the proportion of saturated fatty acids of the backfat. However, a lower proportion of saturated fatty acids was found in the intramuscular neutral lipids from pigs fed outdoors. Pigs reared free-range had significantly (P = 0.0001) higher proportions of C18:1n − 9 in the inner layer and in the intramuscular neutral lipids than the other groups. The grass intake significantly (P = 0.0001) increased the proportion of C18:3n − 3 in the inner and outer fat layers and intramuscular neutral lipids, while the outdoor rearing system not only affected on the proportion of linolenic acid but also C22:5 and C22:6 of the inner backfat layer and intramuscular polar lipids. These results suggest that the outdoor rearing allows a higher accumulation of n − 3 fatty acids maybe due to an increased activity of the desaturase and elongase enzymes. On the other hand, the accumulation of tocopherols was not significantly modified neither by the grass intake nor the outdoor rearing, while differences were detected by the type of feeding (diet vs. acorns/acorns and grass). It is concluded, that the outdoor rearing system affects the nutritional value of meat, mainly by improving the fatty acid composition.