Combined effects of dietary arginine, leucine and protein levels on fatty acid composition and gene expression in the muscle and subcutaneous adipose tissue of crossbred pigs

The cumulative effects of dietary arginine, leucine and protein levels on fat content, fatty acid composition and mRNA levels of genes controlling lipid metabolism in pig longissimus lumborum muscle and subcutaneous adipose tissue (SAT) were investigated. The experiment was performed on fifty-four intact male pigs (DurocxPietrainxLarge WhitexLandrace crossbred), with a live weight ranging from 59 to 92kg. The pigs were randomly assigned to one of six experimental treatments (n 9). The treatments followed a 2x3 factorial arrangement, with two levels of arginine supplementation (0 v. 1%) and three levels of a basal diet (normal protein diet, NPD; reduced protein diet, RPD; reduced protein diet to achieve 2% of leucine, RPDL). The results showed that dietary arginine supplementation did not affect the intramuscular fat (IMF) content and back fat thickness, but increased the total fat in SAT. This effect was associated with an increase in fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD) mRNA levels in SAT, which suggests that arginine might be involved in the differential regulation of some key lipogenic genes in pig muscle and SAT. The increase in IMF content under the RPD, with or without leucine supplementation, was accompanied by increased FASN and SCD mRNA levels. Arginine supplementation did not influence the percentage of main fatty acids, while the RPD had a significant effect on fatty acid composition in both tissues. Leucine supplementation of RPD did not change IMF, total fat of SAT and back fat thickness, but increased 16:0 and 18:1cis-9 and decreased 18:2n-6 in muscle.