The effect of lactic acid bacteria included as a probiotic or silage inoculant on in vitro rumen digestibility, total gas and methane production

Through alterations in silage and rumen fermentation, lactic acid bacteria (LAB) silage inoculants may affect OM digestibility and methane (CH4) emissions. In order 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 several inoculation levels, LAB combinations, and several different basal substrates. In Experiment 1, the effects of 7 LAB on in vitro gas and CH4 production was examined, using dry grass silage as a basal substrate and a LAB inoculation level of 1 × 106 cfu/ml. In Experiment 2, the dose-response effects 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 basal substrate. In Experiment 3, 3 LAB inoculant mixtures were examined while varying the basal substrate. Substrates for experiment 3 were inoculated with LAB prior to ensiling for 3 months as 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 affected 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, L. plantarum (LP) 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. In RS and RCS, an inoculation of a mixture of Lactobacillus plantarum (10%), Lactobacillus buchneri (70%) and Lactococcus lactis (20%) (LM1) tended to increase OM digestibility, while an inoculation of a Lactobacillus buchneri (50%) and Lactococcus lactis (50%) mixture (LM2) and a Lactobacillus plantarum (40%), Lactococcus lactis (30%) and Enterococcus faecium (30%) 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.