Abstract: 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)

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.