Through alterations in silage and rumen fermentation, lactic acid bacteria (LAB) silage inoculants may affect OM digestibility and methane (CH4) emissions. To identify LAB that may have beneficial effects on CH4 emissions and/or OM digestibility in vivo, a series of in vitro gas production trials were conducted to evaluate potential LAB inoculants at several inoculation levels, combinations, and using different substrates. In Experiment 1, the probiotic effects of 7 LAB on in vitro gas and CH4 production was examined, using dry grass silage as a substrate and a LAB inoculation level of 1×106cfu/ml. In Experiment 2, the dose-response probiotic effect of 3 LAB on in vitro total gas and CH4 production were examined using the same dry grass silage as in Experiment 1 as the substrate. In Experiment 3, 3 LAB inoculant mixtures were examined while varying the substrate. Substrates for Experiment 3 were inoculated with LAB prior to ensiling for 3 months and were ryegrass/clover silage (RCS), maize silage (MS) and ryegrass silage (RS, from bales or mini silos). Results from the 3 experiments revealed several patterns in the effects of LAB inoculants on in vitro fermentation. First, not all LAB had a probiotic affect during in vitro fermentation. Of the LAB strains examined in Experiment 1, none had any significant effect on gas production, CH4 production/curve parameters (with the exception of one time point, 72-h, P=0.05), VFA concentration and profile or OM digestibility. In Experiment 2, Lactobacillus plantarum (LP) as a probiotic resulted in significant increases in OM digestibility, and there was a trend for several dose related responses. In Experiment 3 it was demonstrated that LAB show both strain and substrate-specific responses, when added as silage inoculants. In RS and RCS, an inoculation mixture of L. plantarum, Lactobacillus buchneri and Lactococcus lactis (LM1) tended to increase OM digestibility, while an inoculation of L. buchneri and L. lactis mixture (LM2) and of L. plantarum, L. lactis and Enterococcus faecium mixture (LM3) tended to decrease OM digestibility in RCS. These effects were generally mirrored by changes in gas and CH4 production. In MS, no effects were observed on OM digestibility, total gas or CH4 production. Results suggest LAB may be most effective in grass silages (compared to maize silages), and that the LP treatment from Experiment 2, or the LM1 treatment from Experiment 3, may be most promising for evaluation in vivo.

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