# Evaluation of direct-fed microbials as an alternative to ionophores and non-ionophore additives on in vitro ruminal fermentation, gas production kinetics, and digestibility in beef cattle’s forage-based diets

## TL;DR

This study explores whether Bacillus-based microbes can replace chemical additives in cattle feed to improve digestion and fermentation without negative side effects.

## Contribution

The study introduces Bacillus-based direct-fed microbials as a potential alternative to ionophores in cattle feed, showing comparable or better fermentation outcomes.

## Key findings

- DFM increased gas production in early incubation phases compared to control and some ionophores.
- Ionophores like Monensin and Narasin reduced digestion rates and nutrient digestibility.
- DFM did not impair ruminal fermentation and may be a viable alternative to antibiotics.

## Abstract

Two studies were conducted to evaluate the effects of a Bacillus-based direct-fed microbial (DFM) compared to ionophores and non-ionophore additives on in vitro ruminal fermentation parameters, gas production kinetics, as well as dry matter and fiber digestibility using two forage-based diets (medium- and low-quality tropical forages). For Exp. 1, Urochloa brizantha cv. Marandu (CP = 9.64%) was used as the medium-quality substrate (MF), alone or in combination with an energy-protein supplement (EPS), hereafter referred to as MF and MF-S, respectively. These substrates were incubated in triplicate, and six treatments were evaluated: Control (Con—no additive); two DFM levels: DFM1x (1.9 mg), and DFM5x (9.5 mg); Monensin (Mon; 20 ppm); Narasin (Nar; 13 ppm); and Flavomycin (Flavo; 4 ppm). In Exp. 2, U. brizantha cv. Marandu (CP = 3.0%) was used as the low-quality substrate (LF), alone or in combination with EPS, and defined as LF and LF-S, respectively. The additive treatments were the same as described in Exp. 1. In both experiments, an in vitro gas production (GP) system was used in four consecutive 96-h fermentation runs. The average values obtained from three bottles within each incubation were considered as the experimental unit. The data from each experiment were analyzed using a 2 × 6 factorial design. In Exp. 1, there were no significant interactions between substrates and feed additives (P > 0.05) for GP, kinetic parameters, and digestibility. DFM1x and DFM5x and Flavo increased (P < 0.05) GP in the initial hours of incubation, while Mon and Nar reduced it compared to Con (P < 0.01). The rate of digestion for the first pool (K1) was higher for Nar vs. DFM1x, DFM5x, Mon, and Flavo, but did not differ from Con (P < 0.01). Relative to other treatments, Mon reduced K1 (P < 0.01), and Mon and Nar reduced the rate of digestion for the second pool (K2) (P < 0.01). Overall, compared with other treatments, Mon and Nar reduced nutrient digestibility (P < 0.01) and acetate: propionate ratio (P < 0.01). In Exp. 2, substrate × additive interactions were observed for GP (P < 0.05). DFM1x increased (P < 0.01) GP compared with Con when substrate was LF, but did not differ (P > 0.05) from Con when LF-S was used. Mon and Nar reduced (P < 0.05) GP, rate digestion, and increased (P < 0.05) lag time compared to Con, DFM1x, DFM5x, and Flavo. Digestibility was not affected (P > 0.05) by DFM, but ionophores decreased it (P < 0.01) compared to Con. Total VFA did not differ (P = 0.11) among treatments, but Mon and Nar reduced (P = 0.02) acetate compared with Con and DFM1x and increased (P < 0.01) propionate compared with other treatments. These findings suggest, given increasing scrutiny of use of antibiotics and potential antimicrobial resistance uprise, DFM may be a viable alternative to ionophores without impairing ruminal fermentation.

Naturally occurring Bacillus bacteria may boost rumen fermentation in cattle fed forage diets, offering a promising natural alternative to conventional chemical feed additives supplementation.