PSII-27 - Inflammation- and immunity-associated gene expression in the liver and whole blood of crossbred beef cattle with divergent residual feed intake phenotype

Abstract: We investigated the inflammation- and immunity-associated gene expression in the liver and whole blood of crossbred beef cattle with divergent residual feed intake phenotype to identify relevant immune-related biological processes underpinning feed efficiency in beef cattle. Low-RFI beef steers (n = 8; RFI = - 1.93 kg/d) and high-RFI beef steers (n = 8; RFI = + 2.01kg/d) were selected from a group of 56 growing crossbred beef steers (average BW = 261 ± 18.5 kg) fed a high-forage total mixed ration after a 49-d performance testing period. At the end of the 49-d testing period, liver biopsies and blood samples were collected for total RNA extraction and cDNA synthesis. The mRNA expression of 84 genes each related to innate and adaptive immunity was analyzed using pathway-focused PCR-based arrays. The mRNA expressions of genes with fold change ≥ (-) 2.0 and FDR ≤ 0.05 in the blood and liver were determined to be differentially expressed. Out of the 84 immune genes analyzed, the expression of 8 genes in the blood and 20 genes in the liver were upregulated in low-RFI, compared to high-RFI steers. Gene ontology analysis of all the differentially expressed genes in the blood and liver revealed that pathways related to pattern recognition receptor activity, detection of lipopolysaccharide, detection of external biotic stimulus, positive regulation of phagocytosis, positive regulation of vitamin metabolic process, vascular endothelial growth factor production, positive regulation of epithelial tube formation and T-helper cell differentiation were enriched (FDR < 0.05) in Low-RFI beef steers. These results suggest that low-RFI steers have a robust immune repertoire that is capable of prompt response to inflammatory stimuli. This prompt response to inflammation in the Low-RFI group may be characterized by higher protein turnover and increased epithelial cell differentiation, whereby an enhanced quantity of invariant natural killer T-cells and viability of natural killer cells could induce a quicker and more effective response to inflammatory stimuli and consequently contribute to more efficient partitioning of nutrients for growth in these animals.