Differential effects of reduced protein diets on fatty acid composition and gene expression in muscle and subcutaneous adipose tissue of Alentejana purebred and Large White × Landrace × Pietrain crossbred pigs.

The present study assessed the effect of pig genotype (fatty v. lean) and dietary protein and lysine (Lys) levels (normal v. reduced) on intramuscular fat (IMF) content, subcutaneous adipose tissue (SAT) deposition, fatty acid composition and mRNA levels of genes controlling lipid metabolism. The experiment was conducted on sixty intact male pigs (thirty Alentejana purebred and thirty Large White × Landrace × Pietrain crossbred), from 60 to 93 kg of live weight. Animals were divided into three groups fed with the following diets: control diet equilibrated for Lys (17·5 % crude protein (CP) and 0·7 % Lys), reduced protein diet (RPD) equilibrated for Lys (13·2 % CP and 0·6 % Lys) and RPD not equilibrated for Lys (13·1 % CP and 0·4 % Lys). It was shown that the RPD increased fat deposition in the longissimus lumborum muscle in the lean but not in the fatty pig genotype. It is strongly suggested that the effect of RPD on the longissimus lumborum muscle of crossbred pigs is mediated via Lys restriction. The increase in IMF content under the RPD was accompanied by increased stearoyl-CoA desaturase (SCD) and PPARG mRNA levels. RPD did not alter backfat thickness, but increased the total fatty acid content in both lean and fatty pig genotype. The higher amount of SAT in fatty pigs, when compared with the lean ones, was associated with the higher expression levels of ACACA, CEBPA, FASN and SCD genes. Taken together, the data indicate that the mechanisms regulating fat deposition in pigs are genotype and tissue specific, and are associated with the expression regulation of the key lipogenic genes.