Adding Appropriate Fiber in Diet Increases Diversity and Metabolic Capacity of Distal Gut Microbiota Without Altering Fiber Digestibility and Growth Rate of Finishing Pig

Abstract

The digestion ability of pigs to dietary fiber is derived from their intestinal microbiota, especially hindgut microbiota. However, tolerance of pigs to high dietary fiber and the changes of microbiota profile with fiber levels are still unclear. To investigate the changes of gut microbiota with dietary fiber and its relationship with fiber digestibility, we conducted comparative analyses of growth rate, apparent fiber digestibility, gut microbiota and volatile fatty acid (VFA) profiles in Chinese Suhuai pigs feeding diets with different defatted rice bran (DFRB) fiber levels. We found that dietary fiber level had no effect on the growth rate of Suhuai pigs. Although the apparent digestibility of Cellulose, insoluble dietary fiber (IDF) and total dietary fiber (TDF) decreased with dietary fiber level, we found that the apparent digestibility of Cellulose, IDF and TDF of Suhuai pigs was not changed when provided with diet containing 19.10% TDF (as feed basis). The pigs provided with diet containing 19.10% TDF had higher microbial richness, proportions of several fiber-degrading bacteria taxa at genus level and predicted microbial functions (such as carbohydrate metabolism, energy metabolism) in cecum compared to those fed with basal diet. In addition, the fiber-induced increasing of fiber-degrading bacteria promoted the VFAs metabolism, which potentially helped Suhuai pigs to maintain growth rate. However, as TDF reached to 24.11% (as feed basis), the apparent digestibility of fiber decreased and the positive effect on intestine microbiota in caecum were absent. Together, our data suggest that appropriate fiber level could increase the diversity and metabolic capacity of distal gut microbiota to improve the utilization efficiency of fiber resources without altering the growth rate of pigs.

Keywords: 16S rRNA gene sequencing; VFA; caecum; fiber intake; insoluble dietary fiber.

FIGURE 1

Comparison of linear growth rate between each of treatment groups and control. (A) Treatment I and control, (B) Treatment II and control. (C) Treatment III and control. (D) Treatment IV and control. According to the weight change of pigs in the treatment groups and the control, the linear regression was calculated, then the difference between the pair-wise linear regression was compared, respectively. Slope means linear growth rate.

FIGURE 2

Correlation analysis between apparent digestibility of feed and average TDF intake.

FIGURE 3

Diagram of microbial community’s comparison of between treatment groups and control group. Alpha diversity of caecal bacterial communities (A) and colonic bacterial community (B). Scatterplot from PCoA of caecal bacterial communities (C) based on unweighted UniFrac distance and colonic bacterial communities (D) based on Bray_Curtis distance. One-way ANOVA followed by LSD post-hoc test was conducted. *P < 0.05; ns, not significant.

FIGURE 4

The gut microbiota composition of Suhuai pigs at phyla and genera level. (A) Relative distribution of the 20 most dominant bacterial genera and the phyla to which they belong in caecal samples. (B) Relative distribution of the 20 most dominant bacterial genera and the phyla to which they belong in colonic samples. Different shades of color represent different taxa. The pie chart depicts different genera. The outer ring around the pie chart depicts different phyla. Numbers in brackets denote the range of relative abundance of the bacteria. (C) Relative abundance of five fiber-degrading bacteria were significantly higher in treatment II compared to those in the control group (P < 0.01).

FIGURE 5

Comparison of caecal microbial functions between treatment groups and control group. (A) Comparison of the top 10 microbial functions of COG between treatment II, IV with control, respectively. (B) Comparison of the top 10 microbial functions of KEGG between treatment II, IV with control, respectively. One-way ANOVA followed by LSD post-hoc test was conducted. ^#P < 0.01 between treatment II and control group.

FIGURE 6

Correlation network analysis between fiber intake and microbiota. Networks display Spearman rank correlations between the relative abundance of bacteria at genus level and fiber intake in caecum (A) and colon (B). The preceding letters “g” in the bracket represent genus bacteria. Solids represent the correlations with corrected values of 0.00 < P < 0.05, and dashed lines represent the correlations with corrected values of 0.05 ≤ P < 0.10. Red lines represent positive correlation and green lines represent negative correlation.

FIGURE 7

Correlation analysis between the concentrations of VFAs and average TDF intake. (A) Correlation analysis between the concentrations of VFAs in caecum and average TDF intake. (B) Correlation analysis between the concentrations of VFAs in colon and average TDF intake.

FIGURE 8

Correlation network analysis between the concentrations of VFAs and microbiota in caecum. Networks display Spearman rank correlations between the relative abundance of bacteria at genus level and the concentrations of acetate (A), propionate (B), isobutyrate (C), butyrate (D), isovalerate (E), valerate (F), and total VFA (G). Square nodes represent the correlations with corrected values of 0.00 < P < 0.05, and round nodes represent the correlations with corrected values of 0.05 ≤ P < 0.10. Red lines represent positive correlation and green lines represent negative correlation.