Combinations of bacterial cultures, exogenous enzymes, and yeast-based feed additives and their impact on ruminal microbiome.

Our objective was to evaluate the effects of bacteria (), enzymes (amylase, hemicellulose, and xylanase), and yeast as additives on the ruminal microbiome. We hypothesized that inclusion of bacteria, enzymes, and yeast would impact butyric bacterial populations. Eight fermenters were arranged in a duplicated 4 × 4 Latin square with the following treatments: 1) control without additives (CTRL); 2) bacterial culture and enzyme blend (EB); 3) bacterial culture and enzyme blend with a live yeast and yeast culture blend (EBY); and 4) double dose of bacterial culture and enzyme blend and the yeast products blend (2X). We conducted four fermentation periods of 10 d each, with the last 3 d for collection of samples. Overall, 64 solid and liquid samples were analyzed by amplification of the V4 region of bacterial 16S rRNA. Data were analyzed with R and SAS. The following orthogonal contrasts were used: 1) ADD-the control compared to all treatments with additives (CTRL vs. EB, EBY, and 2X); 2) YEAST-treatment without yeast compared to those with yeast (EB vs. EBY and 2X); and 3) DOSE-the single dose of enzymes, bacteria, and yeast compared to the doubled dose (EBY vs. 2X). Family was more abundant when additives were added (ADD). Additives (ADD) also increased relative abundance of and in solid fraction, and of and two members of family in liquid fraction. Yeast (YEAST) decreased relative abundance of and increased abundance of and in solid fraction. Doubling the dose of enzymes and microbial additives (DOSE) decreased the abundance of in solid fraction and in the liquid. Molar proportion of butyrate was highly correlated with abundance of in solid ( = 0.68) and liquid fraction ( = 0.79), and with in liquid ( = 0.70). Our results demonstrate that YEAST decreases abundance of succinate synthesizing bacteria, while DOSE decreases abundance of bacteria that metabolize succinate into propionate. Combined bacteria, enzymes, and yeast increase the relative abundance of specific genera primarily within the family, which may explain the increase in butyrate molar proportion observed with ADD.