Effects of a Bacillus-based direct-fed microbial on in vitro nutrient digestibility of forage and high-starch concentrate substrates

Two experiments evaluated the effects of a Bacillus-based direct-fed microbial (DFM) on in vitro dry matter (DM) and neutral detergent fiber (NDF; experiment 1) and starch (experiment 2) digestibility of a variety of ruminant feedstuffs. In experiment 1, 10 forage sources were evaluated: ryegrass, alfalfa hay, leucaena, corn silage, spinifex, buffel grass, flinders grass, Mitchell grass, Rhodes grass hay, and Queensland bluegrass. Experimental treatments were control (forages with no probiotic inoculation; CON) and forage sources inoculated with a mixture containing Bacillus licheniformis and Bacillus subtilis (3.2 × 10(9) CFU per g; DFM). In vitro DM and NDF digestibility were evaluated at 24- and 48-h post-treatment inoculation. Treatment × hour interactions were noted for IVDMD (in vitro dry matter digestibility) and IVNDFD (in vitro neutral detergent fibre digestibility) (P ≤ 0.05). More specifically, DFM inoculation increased (P ≤ 0.03) IVDMD at 24 h in four forages and increased 48-h IVDMD (P ≤ 0.02) in alfalfa hay, ryegrass, leucaena, and Mitchell grass hay, but opposite results were observed for Queensland bluegrass (P < 0.01). A 24- and 48-h IVNDFD increased following DFM inoculation (P ≤ 0.02) in five forage sources, but reduced for Queensland bluegrass (P < 0.01). When the forages were classified according to their quality, main treatment effects were detected for IVDMD (P ≤ 0.02) and IVNDFD (P < 0.01). In experiment 2, five common cereal grains were evaluated—high-density barley (82 g/100 mL), low-density barley (69 g/100 mL), corn, sorghum, and wheat—under the same treatments as in experiment 1. In vitro starch digestibility (IVSD) was evaluated at 6- and 12-h following treatment inoculation. Treatment × hour interactions were observed for starch digestibility in three out of five concentrate sources (P ≤ 0.001). Inoculation of DFM yielded greater 24-h starch digestibility for high-, low-density barley, and wheat (P ≤ 0.02), but also greater at 48 h in wheat (P < 0.0001). Moreover, mean starch digestibility improved for corn and sorghum inoculated with DFM (P < 0.01). Using a Bacillus-based DFM (B. licheniformis and B. subtilis) improved the mean in vitro DM and NDF digestibility of different forage sources of varying qualities (based on crude protein content). Similarly, IVSD was also greater following DFM inoculation, highlighting the potential of this probiotic to improve nutrient digestibility and utilization in the beef and dairy cattle herd.