29 Impact of insoluble corn-based fiber on fecal microbiome and short chain fatty acid composition in growing pigs

Through the process of fermentation, microbes produce short chain fatty acids (SCFA). Pigs can obtain energy from fibrous feedstuffs through a symbiotic relationship with their gastrointestinal microbiome by absorbing SCFA. By improving our understanding of how the microbiome responds to changes in insoluble dietary fiber, the utilization of fibrous feed ingredients in swine diets may be improved. The objective of this study was to determine the influence of insoluble corn-based fibers (ICBF) over time on the microbial communities and secondary metabolites in the feces of growing pigs. Two replicates of 28 gilts (26.7 ± 2.5 kg BW; PIC800 x Camborough; N=56), were randomly assigned to one of 7 semi-synthetic diets. Dietary treatments included a control (CTL) diet with a formulated total dietary fiber (TDF) value of < 1% and 6 diets with an ICBF replacing 30% of the corn starch in CTL: dehulled degermed corn (DHDG; TDF = 0.89%), ground corn (COR; TDF = 3.80%), corn gluten meal (CGM; TDF = 4.36%), high protein dried distillers grains (HP; TDF = 7.00%), dried distillers grains (DDGS; TDF = 7.93%), and corn bran (BRN; TDF =12.29%). Pigs were individually housed and limit-fed 2.4 times maintenance. On days 10, 20, and 30 feces for 16S rRNA gene microbiota and SCFA analysis were collected. Differences in individual operational taxonomic units (OTU) were compared using Linear Discriminant Analysis Effect Size. Data for alpha diversity metrics and SCFA were analyzed as a mixed model with replicate as a fixed or random effect, respectively, and fixed effects of treatment, day, and treatment by day interactions. Of the top 100 OTU, 89 had significant treatment by day interactions (P< 0.05). Chao1 species richness estimate had significant treatment by day interactions (P<0.01). Day 10 Chao1 index ranged from 510 to 873 for all treatments. From D10 to D20, diets including ICBF resulted in a 3-to-6-fold increase. The Chao1 index was greatest for COR and CGM diets with a slight reduction in DHDG, DDGS, and BRN; there was no change between CTL D10 and CTL D20. ICBF diets were similar from D20 to D30, except for CGM, which had a slight reduction in the Chao1 index on D30 relative to D20. From D20 to D30, CTL had a 5-fold increase but was still reduced relative to all other diets. Percent proportions of acetate, propionate, butyrate, and isobutyrate have significant treatment by day interactions (P< 0.01). Proportions of acetate decreased over time in COR while CTL and DHDG increased. Proportions of propionate decreased over time in CTL, CGM, and BRN, while COR increased. Proportions of butyrate decreased in CTL and DHDG over time. Collectively, these data show how inclusions of ICBF can influence microbiota and SCFA composition.