LAUSR

We examined the effects of two direct-fed microbials (DFM) containing multiple microbial species and their fermentation products on ruminal fermentation, bacterial community and metabolome of beef steers. Nine rumen-cannulated Holstein steers were assigned to 3 treatments arranged in a 3 × 3 Latin square design with three 21-d periods. Dietary treatments were (1) CON (basal diet without additive), (2) PROB (basal diet plus 19 g/d of Commence), and (3) SYNB (basal diet plus 28 g/d of RX3). Commence is a blend of active S. cerevisiae, Enterococcus lactis, Bacillus subtilis, Enterococcus faecium, and L. casei, and their fermentation products. RX3 is a blend of active S. cerevisiae and the fermentation products of S. cerevisiae, Enterococcus lactis, Bacillus licheniformis, and Bacillus subtilis. Daily dry matter intake was calculated. On d 21 of each period, ruminal contents were sampled at 3, 6, 12, and 18 h after feeding for analysis of VFA, bacterial community via 16S rRNA sequencing, and metabolome via chemical isotope labeling liquid chromatography mass spectrometry. There was no effect on DMI. Compared to CON, supplementation of either PROB or SYNB increased or tended to increase (P ≤ 0.10) total VFA, propionate, and valerate concentrations. Compared to CON, PROB reduced (P ≤ 0.05) the relative abundance of Prevotella 1 and Prevotellaceae UCG-001, but increased those of Rikenellaceae RC9, Succinivibrionaceae UCG-001, Succiniclasticum, Ruminococcaceae UCG-014, and Ruminococcaceae UCG-002, whereas SYNB decreased (P ≤ 0.05) the relative abundance of Prevotella 1 and Prevotellaceae UCG-001, and increased those of Prevotella 7, Succinivibrio, Succiniclasticum, and Ruminococcaceae UCG-014. Metabolome analysis revealed that 8 ruminal metabolites, including some amino acids, were increased (P ≤ 0.05) by PROB, whereas no differences were found for SYNB. This study demonstrated that supplemental PROB or SYNB altered the ruminal bacterial community and metabolome differently to achieve a similar ruminal fermentation pattern.