PSXIII-26 Effects of a Bacillus-based probiotics, ionophores, and non-ionophore additives on in vitro gas production kinetics of forage-based diets.

Abstract Feed additives, including probiotics, ionophores, and non-ionophores, can modulate the rumen microbiome, animal performance and immune response. However, most research with these additives has been conducted with high concentrate diets, and few focused on forage-based systems. This study evaluated the effects of a Bacillus-based Direct-Fed Microbial (DFM; Bacillus licheniformis 809 and Bacillus subtilis 810), compared with conventional additives (monensin, narasin, and flavomycin) on rumen fermentation kinetics using an in vitro gas production (IVGP) technique. The experimental design was a 2 × 6 factorial arrangement with two substrates - Urochloa brizantha cv. Marandu (CP = 9.64%) alone or combined with an energy-protein supplement (EPS), and six feed additive treatments: Control (Con - no additive inclusion); two DFM levels (DFM1x:1.9 mg and DFM5x: 9.5 mg), Monensin (Mon: 20 ppm), Narasin (Nar: 13 ppm), and Flavomycin (Flavo: 3 ppm). Substrates were incubated in triplicates over four consecutive 96-h fermentation periods. The IVGP was recorded at 3, 6, 12, 24, 36, 48, 72, and 96 h, and fermentation kinetics (mL/g DM) were estimated using PROC NLIN in SAS. No significant substrate × additives interactions (P > 0.05) were detected; however, independent effects were significant (P < 0.05). The IVGP at 12, 24, 48, and 96 h was greater for forage plus EPS than forage alone (P < 0.001), without altering rates of digestion of both pools (K1 and K2, respectively). The DFM (DFM1x and DFM5x) and Flavo increased IVGP at 12 and 24 h, whereas Mon and Nar decreased it (P < 0.001). At 48 and 96 h, Mon reduced IVGP relative to Con and other additives, which did not differ each other (P < 0.001). At 24 h, DFM inclusion increased IVGP linearly (P < 0.05), however, it did not affect the IVGP in the first pool (V1) compared with the Con and Flavo, while Mon reduced V1. Similar results were observed for the second pool (V2), except Nar that increased V2. Specific K1 and K2 were unchanged with DFM inclusion, but decreased with Mon, whereas Nar increased K1 and decreased K2. Lag time was longer for ionophores (Mon and Nar) and shorter for Flavo than for Con, DFM1x, and DFM5x (P < 0.05). Bacillus-based probiotics increased IVGP in early fermentation, whereas ionophores reduced in vitro digestion rate and cumulative IVGP. These findings suggest that DFM may be a viable alternative to ionophores without impairing ruminal fermentation.