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.
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