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

## TL;DR

This study shows that a new feed additive from Bacillus licheniformis improves dairy cow feed efficiency by changing the rumen microbiota, while monensin has similar effects but with different microbial responses.

## Contribution

The study introduces a new feed additive from Bacillus licheniformis and reveals its distinct effects on rumen microbiota and feed efficiency compared to monensin.

## Key findings

- Bacillus licheniformis fermentation extract (BLFE) alone increased milk yield and feed efficiency without affecting hindgut microbiota.
- Monensin increased energy-corrected milk yield and modulated rumen microbiota differently in primiparous and multiparous cows.
- BLFE and monensin had interactive effects on fecal genera but minimal impact on fecal propionate/acetate and feed efficiency.

## Abstract

Monensin is a feed additive widely used to modify the rumen microbiota composition and thereby improve feed efficiency; meanwhile, new feed additives with similar effects are becoming available. Researchers speculate that feed additives designed to alter the ruminal microbiota can pass intact to the lower gut and influence the microbiota there as well. In this study, monensin and a new feed additive derived from the bacterium Bacillus licheniformis were added to the feed, alone and in combination, to determine if their effects on ruminal and hindgut microbiota, as well as feed efficiency, would be additive in dairy cows. The results, however, highlighted that using the Bacillus licheniformis fermentation extract alone—rather than in combination with monensin—might effectively improve feed efficiency by modulating the rumen microbiota composition rather than that of the lower gut. Monensin differentially modulated ruminal microbiota composition in primiparous and multiparous cows. Monensin increased milk fat content in multiparous cows but did not affect it in primiparous cows, in line with the rumen microbiota composition.

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 Bacillus licheniformis (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, p < 0.05), regardless of the BLFE in the diet. The BLFE tended to increase ruminal Firmicutes/Bacteroidetes (F: B) when fed alone, while alpha and beta diversities remained unmodified. The BLFE increased the abundances of Bifidobacterium (p = 0.02) and Erysipelotrichaceae_UCG-002 (p = 0.01) in RF, whereas monensin increased and decreased the abundances of Oscillospirales_ge (p = 0.02) and an unclassified Clostridia genus (p = 0.03), respectively. The monensin-suppressed Clostridia were negatively associated with ruminal P: A (r = −0.66; p < 0.01) and feed efficiency (r = −0.30; p = 0.04). The BLFE and monensin interactively affected several fecal genera (p < 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 Firmicutes and Bacteroidetes abundances in lactating dairy cows.