Bioprocessed Soy Protein Influences the Fecal Microbiota of Healthy Adult Dogs

Plant-based proteins such as soy protein have a more consistent nutrient profile than animal proteins, but contain anti-nutritional factors such as trypsin inhibitors and oligosaccharides that can negatively affect digestion, increase flatulence, and decrease fecal quality. Bioprocessed soy protein (BSP) is a high-quality protein with lower anti-nutritional factor concentrations that has been shown to alleviate some of the negative effects of soy. A previous study revealed that BSP increased fecal short-chain fatty acid (SCFA) concentrations and decreased fecal putrefactive compounds, suggesting active and beneficial fermentative action in the colon. However, little is known about the effects of BSP on the composition of canine fecal microbiota. The objective of this study was to evaluate the effects of increasing dietary BSP concentration on fecal microbiota of healthy adult dogs. 48 healthy adult Beagle dogs (20 females and 28 males; 3.4 yr mean age; 10.0 kg mean BW) were randomly allotted to one of 6 dietary treatments containing 0 (control), 4, 8, 12, 24, or 48% BSP. The experiment consisted of a 7 d adaptation phase followed by a 14 d treatment period (first 10 d were an adaptation period; last 4 d were used for fecal collections). Extraction of DNA from fresh fecal samples was followed by amplification of the V4 region of the 16S rRNA gene using barcoded primers. High quality sequence data were analyzed using QIIME 1.9.1. and Statistical Analyses of Metagenomic Profiles (STAMP) software 2.1.3. Correlations between microbial taxa and fecal metabolites were assessed using Pearson correlation coefficients. Principal coordinates analysis (PCoA) of weighted UniFrac distances revealed that samples with high dietary inclusion of BSP (24 and 48%) clustered separately from samples with lower dietary inclusion. Alpha diversity measures revealed lower (p<0.05) species richness in dogs fed the control diet compared to those fed 24% BSP. Higher inclusion of BSP (24 and 48%) led to greater (p<0.05) relative abundance of Veillonellaceae. A lower (p<0.05) relative abundance of Clostridium was observed in dogs fed 48% BSP compared to those fed 0, 4, and 8%. A positive correlation (p<0.001) was identified between Clostridium and fecal branched-chain fatty acid concentrations. Relative abundance of Megamonas, a known SCFA producer, was greater (p<0.05) in dogs fed 48% BSP. In conclusion, BSP was shown to significantly shift the fecal microbial communities of healthy adult dogs. Further research is needed to understand the diet-microbe-metabolite relationships identified in this study and apply it to canine health.