Alteration in Gene Expression in the Jejunum Mucosa of Angus Steers with Divergent ADG

The objective of this study was to determine the association of differentially expressed genes in the jejunum of steers with average DMI and high or low ADG. Feed intake and growth were measured in a cohort of 144 commercial Angus steers consuming a finishing ration containing (on a DM basis) 67.8% dry-rolled corn, 20% wet distillers grains with solubles, 8% alfalfa hay, and 4.2% vitamin/mineral supplement. From the cohort, a subset of steers with DMI within ± 0.32 SD of the mean for DMI and the greatest (high ADG) and least (low ADG) steers were chosen for slaughter and jejunum mucosa collection (n = 8 for each group). Dry matter intake (10.1 ± 0.05 kg/d) was not different (P = 0.41) but ADG was greater in the high gain group (1.72 and 2.17 ± 0.02 kg/d for the low and high ADG groups, respectively; P < 0.01). At slaughter, jejunal mucosa was collected and scraped and mRNA was isolated for sequencing. Differentially expressed genes (DEG) were identified using Tophat2/Cuffdiff software. Gene ontology and pathway analyses were performed using the iPathwayGuide software. A total of 13,747 genes were found to be expressed in the jejunum, of which 64 genes were differentially expressed between the 2 groups (corrected P < 0.05). Ten of the genes were up-regulated in the low ADG group and 54 were up-regulated in the high ADG group. Gene ontology analysis resulted in 24 biological process terms found to be over-represented (P < 0.05). Biological process terms included digestion, drug and xenobiotic metabolism, and carbohydrate metabolism. Additionally, 89 molecular function terms were found (P < 0.05) and included metallopeptidase activity, transporter activity, steroid hydrolase activity, glutathione transferase activity, and chemokine receptor binding. Metabolic pathways (n = 28) impacted (P < 0.05) by the DEG included drug and xenobiotic metabolism by cytochrome P450, carbohydrate digestion and absorption, vitamin digestion and absorption, galactose metabolism, linoleic acid metabolism, and mucin type O-glycan biosynthesis. Results from this experiment indicate that cattle with average DMI and greater ADG likely have a greater capacity to handle foreign substances. It is also possible that these cattle with a greater ADG have a greater number of transporters for vital nutrients such as glucose and phosphate. USDA is an equal opportunity provider and employer.