Fecal microbiome and plasma metabolome responses to Bacillus -based direct-fed microbial supplementation in cow-calf pairs from late gestation through weaning

This study evaluated the effects of supplementation of a Bacillus-based direct-fed microbial (DFM) on the plasma metabolome and fecal microbiome of multiparous beef cow-calf pairs. On day 0 (94 ± 19 days prepartum), 296 Brangus crossbred beef cows were randomly assigned to treatments consisting of free-choice access to a trace mineral supplement alone (CON) or combined (BAC) with Bacillus subtilis 810 and B. licheniformis 809 (3 g/head/day; 6.6 × 109 CFU/head/day) from day 0 to 330 (weaning). Blood was collected from cows on days 0, 30, and 60, and from calves at birth, day 150, and day 330 for targeted metabolomics. Fecal samples were collected from cows on days 0, 60, 150, and 330, and from calves on days 150 and 330 for 16S rRNA gene sequencing. On day 30, BAC cows had greater (P ≤ 0.05) plasma concentrations of seven conjugated bile acids and two ceramides, but reduced (P ≤ 0.05) isoleucine, 3-indoleacetic acid, and indoxyl sulfate, with 12 pathways upregulated and 3 downregulated. On day 60, BAC cows had greater (P ≤ 0.05) total diacylglycerol and select diacylglycerol and triacylglycerol species, but reduced (P ≤ 0.05) eicosapentaenoic acid (EPA) and polyunsaturated phosphatidylcholines, with 11 pathways downregulated. Treatment effects were not detected (P ≥ 0.14) for fecal bacterial phyla, genera, or alpha diversity in cows, except for greater (P ≤ 0.04) Clostridium butyricum and C. alkalicellulosi relative abundances in BAC vs. CON cows at weaning. In calves, 103 metabolic pathways were impacted at birth (P ≤ 0.05), with the most upregulated being alanine, aspartate, and glutamate metabolism pathways; BAC calves also had greater (P ≤ 0.04) plasma alanine, aspartate, proline, and EPA concentrations at birth. At day 150, BAC calves exhibited greater total triacylglycerol concentrations (P = 0.01) across 48 individual species and upregulation of MIF-mediated immune regulation pathways. At weaning (day 330), BAC calves had greater (P ≤ 0.05) plasma anserine and select triacylglycerols, but reduced (P ≤ 0.05) ceramides and tended to have reduced (P ≤ 0.10) branched-chain amino acids, with 17 metabolic pathways downregulated. These findings indicate that gestation-to-weaning Bacillus-based DFM supplementation altered the plasma metabolome of beef cow-calf pairs, with limited effects on the fecal microbiome, and these changes coincided with the previously reported improvements in calf preweaning growth, post-weaning immune response, and carcass quality.