Methane Mitigation Potential of Tannins and their Impact on Digestibility of Nutrients In-vitro

The study was taken up to assess the effect of the pure tannins viz. catechin hydrate, gallic acid, tannin acid and ellagic acid supplemented individually at 1 to 5% levels of the substrate DM (wheat straw) on the in vitro methane production and fiber degradation in a 4x7 factorial design. Irrespective of the type of tannin, the net gas production (NGP) in positive control and tannin supplemented groups (1–5% level) was higher (P<0.01) than normal control. The NGP and partitioning factor (PF) of positive control and tannin supplemented groups up to 4% level were similar, but depressed (P<0.01) at 5% level. The digestibility of NDF and true OM was depressed (P<0.01) at all the levels of tannin supplementation. However, ME availability was not affected by tannin supplementation. The effect of tannins, irrespective of its level revealed that the NGP was depressed (P<0.01), while digestibility of nutrients and ME availability were depressed numerically (P>0.05) in the ellagic acid supplemented group, as compared to other tannins supplemented groups. Irrespective of type of tannins, the TVFAs, acetate and A: P ratio were higher (P<0.01) in positive control than normal control. The TVFAs, acetate and propionate production in tannin supplemented groups was lowest (P<0.01) at 1% level as compared to positive control. Irrespective of the level of tannins, the TVFAs, acetate and propionate production was higher (P<0.01), while A: P ratio was lowest (P<0.01) from catechin hydrate as compared to other tannin supplemented groups. Beyond 2% there was significant depression (P<0.01) in methane production as compared to positive control. Between 3 and 4% levels, there was no difference, but again at 5% there was depression (P<0.01) in methane production. Irrespective of level of tannins, methane production was lowest (P<0.01) in the ellagic acid supplemented group, while the highest (P<0.01) was observed in catechin hydrate supplemented group. It was concluded that ellagic acid supplemented at 3% of substrate mitigated the methane production, depressed the digestibility and VFA production, but without affecting ME availability.