The effect of lactic acid bacteria as probiotics or silage inoculants on in vitro rumen digestibility, total gas and methane production

Lactic acid bacteria (LAB) included as a probiotic or silage inoculant may affect rumen fermentation, OM digestibility and methane (CH4) emissions in cattle. Therefore, 2 in vitro gas production trials were conducted to pre-screen several potential LAB inoculants at several inoculation levels, using different LAB mixtures, and on different silage substrates. In Experiment 1 the dose-response effects of 3 LAB inoculants added as probiotics (0.0, 5 × 105, 1 × 106 and 5 × 106 cfu/ mL) on in vitro total gas and CH4 production were examined using grass silage as the substrate. In Experiment 2, 3 LAB inoculant mixtures were examined while varying the substrate. Substrates were inoculated with LAB before ensiling, and were ryegrass/clover (RCS), corn (CS) and ryegrass (RS) silage. Data were analyzed with proc MIXED of SAS with LAB inoculant × dose as a fixed effect, and dose was analyzed via orthogonal polynomial contrasts (Experiment 1), and using substrate, inoculation and substrate × inoculation as fixed effects (Experiment 2). Results showed that not all LAB affected in vitro fermentation. In Experiment 1, L. plantarum (LP) but not L. lactis (LL) or a 1:1 mixture of LL and LP, resulted in significant increases in OM digestibility (P = 0.023), and there was a trend for several dose related responses. In Experiment 2, LAB showed both strain and substrate-specific responses. In RS, an inoculation of a mixture of L. plantarum, L.buchneri and L. lactis (LM1) increased OM digestibility, while inoculations of L. buchneri and L.lactis (LM2) and L. plantarum, L. lactis and E. faecium (LM3) decreased OM digestibility in RCS (inoculation P <0.001). These effects were generally mirrored by changes in gas and CH4 production. In CS, no effects were observed on OM digestibility, total gas or CH4 production. From these results we conclude that LAB may be most effective in grass based silages (compared with corn) for altering OM digestibility, and that the LP treatment from Experiment 1, or the LM1 treatment from Experiment 2, may be most promising for evaluation in vivo.