403 Whole blood immune gene expression in Angus bulls with divergent residual feed intake expected progeny differences.

Abstract Our objective was to examine the differences in the whole-blood mRNA expression profiles of immune-related genes in Angus bulls with either negative or positive residual feed intake expected progeny differences (RFI-EPDs). Twenty Angus bulls with the most negative (n = 10; RFI-EPD= -0.29) and most positive (n = 10; RFI-EPD= 0.26) RFI-EPD values were selected from a group of 106 Angus bulls (Average body weight (BW) = 376 ± 36 kg; 370 ± 1.3 d of age) after a 78-day feed efficiency testing period. At the end of this testing period, blood samples were collected for RNA extraction followed by the mRNA expression analysis of 84 genes involved in innate and adaptive immunity using pathway-focused PCR-based arrays. Differentially expressed genes were determined using false discovery rate (FDR) ≤ 0.10. Results from the analysis revealed a total of 5 differentially expressed genes (DEGs; FDR ≤ 0.10) in bulls with divergent RFI-EPD values. We found IL23A to be upregulated, while IL18, TRAF6, TLR2, and MX1 were downregulated in negative RFI-EPD bulls, compared to the positive group. Gene ontology analysis of the DEGs indicated the enrichment of different biological pathways linked to innate immune response, NF-κB signaling, cytokine and T-cell regulation, lipopolysaccharide mediated signaling pathway, and cellular response to bacteria. These findings revealed that negative RFI-EPD bulls exhibit mRNA expression of genes directly related to immune cell function and biological pathways involved in the activation of antimicrobial mechanisms, pathogen recognition mechanisms, and inflammatory response.