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The effect of divergent selection for residual feed intake on cytokine gene expression in pigs following an ex vivo liposaccharide challenge
Pathogenic microbes influence pig performance by stimulating an inflammatory immune response and disrupting metabolism. To date, little research has been undertaken to examine the effect of divergent selection for residual feed intake (RFI) on the immune system. The objective of this study was to examine the effect of divergent selection for RFI on colonic inflammatory cytokine gene expression following an ex vivo Lipopolysaccharide (LPS) challenge. Male pigs (n=75; initial BW 22.42kg (SD = 2.03)) were fed a standard finishing diet (12.5 g/kg lysine and 14.5 MJ/kg Digestible Energy) for 43 days to evaluate feed intake and growth for the purpose of calculating RFI. Phenotypic RFI was calculated as the residuals from a regression model regressing DMI on ADG and midtest BW0.75 (MWT). On day 43, 16 animals (average weight 85kg, Std2.84kg), designated 8 high RFI (HRFI) and 8 low RFI (LRFI) were slaughtered. Colonic tissue was collected and stimulated for three hours ex vivo with LPS. QPCR was performed to analyse the expression of IL-1, IL-6 IL-8, IL-10, Il-17, TNF-α and IFN-γ. As expected LRFI pigs had lower (P<0.001) ADFI (2.44kg vs. 1.87kg sem 0.04) and improved feed conversion ratio (1.96 vs. 2.48, sem 0.01) than HRFI pigs with no difference in ADG or MWT. Stimulation of the colonic tissue with LPS increased expression of IL-8 (P<0.05), TNF-α (P<0.0001), IL-10 (P<0.05), IL-1 (P<0.001), IFN-γ (P<0.05) and IL-6 (P<0.001) in both HRFI and LRFI pigs. There was an interaction between RFI and LPS challenge for the expression of IL-8 (P<0.05) and IL-1 (P<0.01) and IFN-γ (P<0.05). Following the LPS challenge there was an increase in the expression of IL-1 (P<0.01) and IL-8 (P<0.05) and IFN-γ (P<0.05) in the HRFI pigs, with no change in the LRFI pigs. There was no difference between RFI groups for IL-10 and IL-17. The upregulation of pro-inflammatory cytokines has an adverse effect on the gut mucosa and the reduced expression of the pro-inflammatory cytokines in this study could partly explain the increased efficiency in LRFI pigs.
Keywords:
Residual Feed Intake: Cytokine: Pigs