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

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.

Exploring a Possible Link between the Intestinal Microbiota and Feed Efficiency in Pigs

“…However, this study is one of the first to exploit this technology to examine the intestinal microbiota among pigs of varying FE. The metric used for FE was RFI, and ranking pigs according to this measure was particularly useful, as it allowed the selection of pigs that consume less feed to achieve the same weight gain, in agreement with previous findings for pigs divergent in RFI (14,31). To minimize the variability in FE due to external factors, pigs were ranked by RFI within litter (to control for genetic influences), and all pigs were subjected to the same management, environmental, and nutritional conditions.…”

“…In addition, bacterial diversity within the intestinal tract was found to be higher in pigs with heavier body weights and improved growth rates (3,21). However, to our knowledge, only one study to date has investigated the association between FE in pigs and the intestinal microbiota (14). It demonstrated an increased abundance of Lactobacillus in the cecum of more feed-efficient pigs; however, only Firmicutes, Bacteroidetes, Bacteroides, Lactobacillus, and Enterobacteriaceae were measured (by quantitative PCR).…”

“…In recent years, the pig microbiome has become the focus of much attention (14)(15)(16)(17)(18). The porcine intestinal microbiota is dominated at the phylum level by Firmicutes, Bacteroidetes, and Proteobacteria (3,4,19,20).…”

“…It demonstrated an increased abundance of Lactobacillus in the cecum of more feed-efficient pigs; however, only Firmicutes, Bacteroidetes, Bacteroides, Lactobacillus, and Enterobacteriaceae were measured (by quantitative PCR). Pigs with better FE also tended to have higher concentrations of total VFAs in the cecum and butyric acid in the colon, which may be explained by differences in microbial composition and function (14,23).…”

Finishing pigs that are divergent in feed efficiency show small differences in intestinal functionality and structure

“…Some studies reported an enhanced ileal digestibility of energy and expression of SGLT1 and GLUT2 in the jejunum of growing pigs [3,14], whereas other did not find RFI-related differences for digestive efficiency [2,12]. Likewise, gene expression data indicated that the ileal mucosal tight-junction-protein expression and innate immune signaling pathways may play a minor role for variation in RFI of pigs in an unchallenged condition [4,5]. However, serum acute-phase-proteins and ileal inflammation markers indicated a stronger immune response in high compared to low RFI pigs [5].…”