The Effect of Divergence in Feed Efficiency on the Intestinal Microbiota and the Intestinal Immune Response in Both Unchallenged and Lipopolysaccharide Challenged Ileal and Colonic Explants.

Stafford Vigors,Alan K Kelly,Cormac J O’Shea,Torres Sweeney,John V O’Doherty,José A Bengoechea

doi:10.1371/journal.pone.0148145

Abstract

Feed efficiency is an important trait in pig production, with evidence to suggest that the efficiencies of a variety of biological systems contribute to variation in this trait. Little work has been conducted on the contribution of the intestinal innate immune response to divergence in feed efficiency. Hence, the objective of this study was to examine select bacterial populations and gene expression profiles of a range of targets relating to gut health and immunity in the intestine of pigs phenotypically divergent in feed efficiency in: a) the basal state; and (b) following an ex-vivo lipopolysaccharide (LPS) challenge of ileal and colonic tissue. Male pigs (initial BW 22.4 kg (SD = 2.03)) were fed a standard finishing diet for the final 43 days prior to slaughter to evaluate feed intake and growth for the purpose of calculating residual feed intake (RFI). On day 115, 16 animals (average weight 85 kg, SEM 2.8 kg), designated high RFI (HRFI) and low RFI (LRFI) were slaughtered. The LRFI pigs had increased lactobacillus spp. in the caecum compared to HRFI pigs (P < 0.05). RFI groups did not differ in the expression of the measured genes involved in the innate immune system in the basal ileal or colonic tissues (P > 0.10). Interestingly, there was an interaction between RFI and LPS for the cytokines IL-8, IL-1, IL-6, TNF-α, Interferon-γ (IFN-γ) and SOCS3, with the LRFI group having consistently lower gene expression in the colon following the LPS challenge, compared to the HRFI group. The lower gene expression of SOCS and cytokines following an ex vivo LPS challenge supports the theory that a possible energy saving mechanism exists in the intestinal innate immune response to an immune challenge in more feed efficient pigs.

Highlights

Residual feed intake (RFI) is a useful trait in understanding the biological mechanisms that influence feed efficiency [1,2,3]
The LRFI pigs had lower average daily feed intake (ADFI) than pigs ranked as MRFI or HRFI (P < 0.001)
The LRFI pigs had a lower feed conversion ratio (FCR) than pigs ranked as MRFI or HRFI (P < 0.001)

Summary

Introduction

Residual feed intake (RFI) is a useful trait in understanding the biological mechanisms that influence feed efficiency [1,2,3]. Maintaining a competent immune system and mounting effective immune responses is metabolically costly to the host, necessitating trade offs with other nutrient-demanding processes such as growth, reproduction and thermoregulation [4]. Previous research has demonstrated that feed efficient pigs have enhanced antimicrobial enzyme activity, lower serum IL-8, myeloperoxidase and endotoxin levels [2]. The relationship between feed efficiency and the intestinal innate immune response is not fully understood. The innate immune response is the initial non-specific acute phase response to an infection compared to the long term B- and T- cell mediated adaptive or acquired immune response. The innate immune response is considered more metabolically costly than the adaptive immune response and it has been hypothesised that activation of the innate immune system could have measurable effects on feed efficiency [5]. The proportion of lysine directed to the immune system has been shown to increase from 2 to 9%, a fact which illustrates the nutritional cost of the immune response to infection [6]

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