Effects of a Bacillus licheniformis Fermentation Extract and Monensin on the Rumen and Hindgut Microbiota Composition of Lactating Dairy Cows

This research reports ruminal and fecal microbiota composition of lactating dairy cows enrolled in a study aimed at investigating the effects of a fermentation extract derived from <i>Bacillus licheniformis</i> (BLFE), monensin (Rumensin^®; R), and their interactions on feed efficiency (FE, FE = milk yield/DMI). In a completely randomized design, 48 Holstein cows at 108 ± 35 days in milk were matched for parity and assigned to monensin (0 or 17.6 g/kg of DM) and BLFE (0 or 166 mg/kg of DM) in a 2 × 2 factorial arrangement. Treatments were fed daily for 63 d, including a 21 d adaptation period followed by a 42 d measurement period (P2). On d 38 and d 39 of P2, rumen-fluid (RF) and fecal samples were collected. DNA from RF and feces was sequenced using 16S rRNA gene-amplicon sequencing on an Illumina MiSeq platform. Fecal and RF volatile fatty acid (VFA) concentrations were analyzed, and propionate/acetate (P: A) was determined. The BLFE increased milk yield (3.3 kg/d) and FE (1.20 to 1.28), when fed alone rather than with monensin, while monensin increased energy-corrected milk yield (2.5 kg/d, <i>p</i> < 0.05), regardless of the BLFE in the diet. The BLFE tended to increase ruminal <i>Firmicutes</i>/<i>Bacteroidetes</i> (F: B) when fed alone, while alpha and beta diversities remained unmodified. The BLFE increased the abundances of <i>Bifidobacterium</i> (<i>p</i> = 0.02) and <i>Erysipelotrichaceae_</i>UCG-002 (<i>p</i> = 0.01) in RF, whereas monensin increased and decreased the abundances of <i>Oscillospirales_</i>ge (<i>p</i> = 0.02) and an unclassified <i>Clostridia</i> genus (<i>p</i> = 0.03), respectively. The monensin-suppressed <i>Clostridia</i> were negatively associated with ruminal P: A (r = -0.66; <i>p</i> < 0.01) and feed efficiency (r = -0.30; <i>p</i> = 0.04). The BLFE and monensin interactively affected several fecal genera (<i>p</i> < 0.05), but they had negligible or weak correlations with fecal P: A and FE. Overall, the results showed the ability of dietary supplementations of monensin and BLFE to increase milk production performance and FE by modulating ruminal rather than lower-gut microbiota composition, this is predominantly attributed to the ratio between the <i>Firmicutes</i> and <i>Bacteroidetes</i> abundances in lactating dairy cows.