Influence of postruminal casein infusion and exogenous glucagon-like peptide 2 administration on the jejunal mucosal transcriptome in cattle
The objective of the current study was to evaluate the effects of postruminal casein infusion and exogenous glucagon-like peptide 2 (GLP-2) administration on transcriptomic pathways and functions of the jejunal mucosa in cattle using next-generation RNA sequencing. Twenty-four Holstein steers [250 ± 23 kg body weight (BW)] received a continuous abomasal infusion of 3.94 g raw corn starch/kg of BW combined with either 0 or 1.30 g casein/kg of BW for 7 d. Steers received subcutaneous injections in two equal portions daily of excipient (0.5% bovine serum albumin) or 100 µg GLP-2/kg of BW per day. At the end of the 7-d treatment period, steers were slaughtered for collection of the jejunal mucosa.  Total RNA was extracted from jejunal mucosal tissue, strand-specific cDNA libraries were prepared, and RNA sequencing was conducted to generate 150-bp paired-end reads at a depth of 20 M reads in each direction. Differentially expressed genes (DEG), KEGG pathway enrichment, and gene ontology enrichment between treatments were determined based on the FDR-corrected P-value. Postruminal casein infusion downregulated (padj < 0.05) 7 genes of the jejunal mucosa and did not result in any enriched KEGG pathways or gene ontologies. Exogenous GLP-2 administration upregulated (padj < 0.05) 667 DEGs, 26 KEGG pathways, 198 biological processes, 56 cellular components, and 60 molecular functions. Exogenous GLP-2 downregulated (padj < 0.05) 1101 DEGs, 14 KEGG pathways, 270 biological processes, 105 cellular components, and 46 molecular functions. Enrichment analyses revealed that exogenous GLP-2 administration affected several pathways involving mucosal growth, nutrient digestion, absorption, and metabolism, and intestinal barrier function. Results of the current study identified pathways affected by exogenous GLP-2 administration that could have implications for improved animal growth and feed efficiency in cattle. This research generated novel targets for future research to elucidate mechanisms of GLP-2-mediated responses in the jejunal mucosa. Overall design: Steers were transferred to metabolism stalls (1.2 m x 2.4 m) for the 7-d treatment period. Due to limited stall space and infusion apparatus, steers were stratified by BW into 6 replicate blocks. Steers were then randomly assigned to one of four treatments within each replicate block. The experimental design was a randomized complete block design with a 2 ? 2 factorial arrangement of treatments. All steers were abomasally infused with 3.94 ? 0.245 g raw corn starch ? kg BW-1 ? d-1. Along with raw corn starch, steers were abomasally infused with either water or 10% (wt:wt) sodium caseinate solution to provide 0 or 1.30 ? 0.299 g sodium caseinate ? kg BW-1 ? d-1. Additionally, steers received subcutaneous injection treatments in two equal portions daily. Subcutaneous injection treatments were either vehicle (5 g/L bovine serum albumin (BSA) diluted in 9 g/L NaCl) or 100 µg GLP-2 in vehicle ? kg BW-1 ? d-1. This resulted in four treatments: 1) abomasal water + vehicle injection (control), 2) abomasal water + GLP-2 injection (GLP-2), 3) abomasal 10% sodium caseinate solution + vehicle injection (casein), and 4) abomasal 10% sodium caseinate solution + GLP-2 injection (casein + GLP-2). All steers received abomasal infusion and subcutaneous injection treatments for 7 d.