Dietary conjugated linoleic acids affect tissue lipid composition but not de novo lipogenesis in finishing pigs

Overview & Synopsis

Dietary conjugated linoleic acids (CLA) have been reported to profoundly affect lipid metabolism and to act as repartitioning agents. Currently, little is known about their effect on the fatty acid profile of tissue lipids in pigs. In the present study we determined the lipid composition of the backfat inner (BFI) and outer layer (BFO), omental fat (OF) and intramuscular fat (IMF) of the longissimus dorsi muscle in 24 Swiss Large White pigs fed diets supplemented either with 2% CLA-enriched oil (containing 58.9 g CLA isomers$\cdot$100 g$^{-1}$ of total fatty acids), linoleic acid-enriched oil (SO), or lard (LA). Animals were individually penned at 70 kg live weight and fed 2.8 kg$\cdot$d$^{-1}$ of the respective diet to slaughter at 105 kg. Growth performance, carcass characteristics and muscle measurements were not significantly affected by the dietary fats, although average daily weight gain and feed conversion ratio tended to be numerically improved 5-7% in the CLA-fed pigs compared to pigs of the other two treatments. Independent of the tissue, pigs fed the CLA diet exhibited higher levels of saturated fatty acids ($P < 0.05$) and lower levels of monounsaturated fatty acids ($P < 0.05$). By contrast, there was no difference in the distribution pattern of the saturated fatty acids between the LA and SO groups, but pigs fed the SO diet had lower monounsaturated and higher polyunsaturated fatty acid levels compared to those fed the LA diet. The CLA content of the BFO, BFI and OF was similar and did not indicate a preferential incorporation in one of the tissues. Compared to the adipose tissue, approximately 67% lower total CLA concentrations were found in the IMF. The in vitro activity of lipogenic enzymes was not altered by the dietary fat suggesting that lipogenesis was not affected by CLA. The distinct shift towards higher deposition of saturated fatty acids and lower deposition of monounsaturated fatty acids indicated a potential down-regulation of $\Delta$9-desaturase activity by dietary CLA.