PSXIII-22 Impact of feed additives on in vitro dry matter and fiber digestibility of forage-based diets.

Abstract The inclusion of additives in energy-protein supplements (EPS) can be an important tool for improving rumen fermentation of forage-based diets. While some additives enhance fiber digestibility by stimulating cellulolytic bacteria in the rumen, others may have deleterious effects. We hypothesized that the inclusion of a Bacillus-based direct-fed microbial (DFM) would increase in vitro dry matter and fiber digestibility of forage-based diets, whereas both ionophores and non-ionophores additives would have the opposite effect decreasing in vitro digestibility. This study was conducted to evaluate the effects of a Bacillus-based DFM blend containing Bacillus licheniformis 809 and Bacillus subtilis 810 in comparison with ionophores and non-ionophore additives on in vitro dry matter and fiber digestibility in forage-based diets. The experimental treatments evaluated using a 2 × 6 factorial arrangement design with two substrates - Urochloa brizantha cv. Marandu (CP = 9.64%) alone or combined with a PES, 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). The additives were diluted in water (DFM and Flavo) or ethanol (Mon and Nar). Three rumen-cannulated ½ Nellore - Angus steers were used as donor of fresh rumen fluid. The incubations were performed in four consecutive 96-h fermentation runs to evaluate in vitro dry matter digestibility (IVDMD), neutral detergent fiber (IVNDFD), and acid detergent fiber (IVADFD) at 24, 48, and 96 h. The contents were filtered using Ankom® F57 bags, then oven-dried at 105°C for 24 h. Data were analyzed using PROC GLIMMIX of SAS (version 9.4). There were no significant interactions between substrate and feed additives (P > 0.05) for any of the evaluated variables. The IVDMD and IVNDFD were higher for forage plus EPS compared with forage alone at all evaluation times. Overall, DFM (DFM1x and DFM5x), and Flavo did not modify IVDMD, IVNDFD and IVADFD compared with Control, whereas Mon and Nar decreased these parameters. Increasing the DFM dose did not improve fiber digestibility. In conclusion, the inclusion of DFM did not enhance in vitro dry matter or fiber digestibility, whereas ionophores had deleterious effects on the in vitro digestibility.