T100. Evaluating the effects of tannins on the extent and rate of in vitro measured gas and methane production using the Automated Pressure Evaluation System (APES) W. F. Pellikaan*, E. Stringano, J. Leenaars, D.J.G.M. Bongers, S. van Laar!van Schuppen, J. Plant and I. Mueller!Harvey
An in vitro study was conducted to investigate the effect of tannins on the extent and rate of gas and methane production, using an automated pressure evaluation system (APES) that was modified to allow methane measurement. In this study three condensed (CT; Quebracho, Grapeseed extract, Tea tannins) and four hydrolizable tannins (HT; Tara tannins, Valonea, Myrabolan, Chestnut) were evaluated, with lucerne as the control substrate. Tannins were added to the substrate at an effective concentration of 10% either with or without polyethylene glycol (PEG6000), and incubated for 72 h in a pre!warmed buffered medium mixed with rumen liquid pooled from four lactating dairy cows. After inoculation fermentation bottles were immediately connected to the APES to measure total cumulative gas production (organic matter corrected volume, OMCV). The lids of the fermentation bottles contain an opening which is normally gas!tight sealed with a brass cap. The brass caps were modified to allow sampling from the bottle headspace using a gas!tight syringe (25μL, Hamilton). To ensure fully gas!tight and closed fermentation system rubber septa were placed in the brass caps. During the incubation period 10 gas samples were taken from the bottle headspace at time t=1, 4, 7, 11, 15, 23, 46, 52 and 68 h, and analysed on methane by gas chromatography. A Gompertz model was fitted to the methane concentration patterns and model estimates were used to determine the total cumulative methane production (OMCV_CH4). Addition of Quebracho reduced the OMCV significantly (P=0.003) whilst the other tannins did not seem to affect OMCV distinctly. The addition of PEG resulted in an increase in OMCV for Quebracho (P=0.003), Valonea (P=0.064) and Grapeseed extract (P=0.078), suggesting a potentially undesirable effect of these tannins on the extent of fermentation. Addition of Quebracho and Grapeseed extract significantly reduced the maximum rate of gas production (P=0.003), which suggests that microbial activity is seriously affected by these tannins. With respect to methane production Quebracho, Valonea, Myrabola and Grapeseed gave a significant decrease in the OMCV!CH4 and the maximum rate of gas production (P=0.009). Addition of Chestnut extract, Tara tannins and Tea tannins did not seem to affect total gas production or methane production. The current study showed that Valonea and Myrabola gave the most promising results in reducing methane production without having negative effects on the total gas production.