Corn oil or corn grain supplementation to steers grazing endophyte-free tall fescue. II. Effects on subcutaneous fatty acid content and lipogenic gene expression.

Twenty-eight Angus steers (289 kg) were finished on a high-concentrate diet (85% concentrate: 15% roughage; CONC), or endophyte-free tall fescue pastures with corn grain supplement (0.52% of BW; PC), corn oil plus soybean hull supplement (0.10% of BW corn oil plus 0.45% of BW soybean hulls; PO), or no supplement (pasture only; PA). Subcutaneous adipose tissues were processed for total cellular RNA extraction and fatty acid composition by GLC. Relative expression of genes involved in lipogenesis [fatty acid synthase (FASN), acetyl-CoA carboxylase, lipoprotein lipase, stearoyl-CoA desaturase (SCD)] and activators of transcription [(peroxisome proliferator-activated receptor-gamma), C/EBPalpha, sterol regulatory binding protein-1, signal transducer and activator of transcription-5, and Spot-14] was determined by real-time quantitative PCR. Housekeeping gene (glyceraldehyde 3-phosphate dehydrogenase and beta-actin) expression was used in analysis to normalize expression data. Total fatty acid content was greatest (P < 0.001) for CONC and least (P < 0.001) for PA. Supplementation of grazing cattle increased (P < 0.001) total fatty acid content compared with PA, but concentrations were less (P < 0.001) than for CONC. Myristic and palmitic acid contents were greater (P < 0.001) for CONC than for PO and PC, which were greater (P < 0.001) than for PA. Stearic acid content was greater (P < 0.01) for PO than for CONC, PC, and PA. Finishing on CONC increased (P < 0.001) total MUFA content by 68% compared with PA. Corn grain supplementation increased (P < 0.001) MUFA content compared with PA; in contrast, MUFA content did not differ (P > 0.05) between PO and PA. Corn oil supplementation increased (P < 0.001) trans-11 vaccenic acid content in subcutaneous fat by 1.2-, 1.7- and 5.6-fold relative to PA, PC, and CONC, respectively. Concentrations of the cis-9, trans-11 CLA isomer were 54, 58, and 208% greater (P < 0.01) for PO than for PA, PC, and CONC, respectively. Corn grain supplementation to grazing steers did not alter (P > 0.05) the cis-9, trans-11 CLA isomer compared with PA. Oil supplementation increased (P < 0.001) linoleic acid (C18:2) content by 56, 98 and 262% compared with CONC, PC, and PA, respectively. Relative mRNA expression of SCD was upregulated (P < 0.001) by 46-, 18- and 7-fold, respectively, for CONC, PC, and PO compared with PA. Relative FASN mRNA expression was also upregulated (P = 0.004) by 9- and 5-fold, respectively, for CONC and PC compared with PA. Grain feeding, either on CONC or supplemented on pasture, upregulated FASN and SCD mRNA to increase MUFA and de novo fatty acids in subcutaneous adipose tissue. Upregulation of SCD with grain feeding and reduced tissue CLA concentrations suggest that the decreased CLA concentrations were the result of limited substrate (trans-11 vaccenic acid) availability.