Does growth path influence beef lipid deposition and fatty acid composition?

Despite the recent advances in transcriptomics, gene expression studies addressing cattle´s skeletal muscle adaptations in response to compensatory growth are warranted, particularly regarding lipid metabolism due to its impact in meat sensory and nutritional traits. In the present study, in comparison to ad libitum feeding, a period of feed restriction was used in order to understand the changes in bull´s lipid metabolism and gene expression of the adipogenic and lipogenic pathways after re-alimentation. Thus, 40 young Alentejana bulls were either fed ad libitum (CG group) from 9 to 18 months of age or subjected to food restriction from 9 to 15 months of age, and fed ad libitum until 24 months of age (DG group). The intramuscular fat (IMF) and total fatty acids (FA) contents were similar between groups. The major FA (>2%) contents were similar (16:0, 16:1c9, 18:1c9 and 18:2n-6) between treatments with the exception of 18:0 content that was 15% lower in DG than in CG and 20:4n-6 that tended to be greater on DG bulls. Regarding minor FA (<2%), the DG group presented greater proportions (P<0.01) of 17:1c9, 18:1t9, 18:1t10 (, 18:1c11), 18:1c13, 18:3n-6, 22:0, 22:4n-6 and 22:6n-3 and lower (P<0.05) proportions of 20:0, 18:1t16+c14, and branched chain FA (iso-15:0, anteiso-15:0, iso-16:0 and anteiso-17:0) than the CG group. Delta-9 desaturase activity indices were consistently greater (P<0.05) in DG, when compared to the CG group. Regarding microarray analysis, differentially expressed genes between CG and DG bulls were grouped in 5 main biological functions: lipid and nucleic acid metabolisms, small molecule biochemistry, molecular transport and translational modification. Discontinuous growth down-regulated the expression of ACACB (FC (fold-change) = 1.32), FABP3 (FC = 1.45), HADHA (FC = 1.41) and SLC37A4 (FC = 1.40) genes, when compared to the CG system (FDR<0.05). In contrast, in the CG bulls, the expression of ELOVL5 (FC = 1.58) and FASN (FC = 1.71) was down-regulated when compared to DG bulls. These results were confirmed to be significant (P<0.05) in the case of ELOVL5, FASN and SLC37A4, and almost significant for FABP3 by qRT-PCR analysis. The SCD1 and SCD5 gene expressions were not found to be affected by growth path. These results contribute to the still scarce knowledge about the mechanisms involved in fatty acid metabolism during compensatory growth which have decisive role on meat quality produced in Mediterranean areas.