Effects of condensed tannins from Leucaena on methane production, rumen fermentation and populations of methanogens and protozoa in vitro

Different levels of purified condensed tannins (CT) extracted from Leucaena leucocephala hybrid-Rendang (LLR) were investigated for their effects on CH4 production, rumen fermentation parameters such as pH, dry matter (DM) degradability, N disappearance and volatile fatty acid (VFA) concentrations, as well as on populations of rumen methanogenic archaea and protozoa in vitro. Purified CT concentrations of 0 (control), 10, 15, 20, 25 and 30 mg, and 500 mg of oven dried guinea grass (Panicum maximum) with 40 ml of buffered rumen fluid were incubated for 24 h using an in vitro gas production procedure. Total gas (ml/g DM) decreased at a decreasing rate (linear P < 0.01; quadratic P < 0.05) with increased levels of CT inclusion. CH4 production (ml/g DM) decreased at a decreasing rate (linear P < 0.01; quadratic P < 0.01) with increasing levels of CT. Total VFA concentration (mmol/L) decreased at a decreasing rate (linear P < 0.01; quadratic P < 0.01) with increasing CT inclusions. In vitro DM degradation and N disappearance declined linearly (P < 0.01) with increasing levels of CT. Estimates of rumen methanogenic archaea and protozoa populations using microbiological methods and real-time PCR assay showed linear reductions in total methanogens (P < 0.01) and total protozoa (P < 0.01) with increasing levels of CT. Methanogens in the order Methanobacteriales also declined, but with quadratic and cubic aspects. Results suggest that CT from LLR at a relatively low level of 15 mg of CT/500 mg DM reduce CH4 production by 47%, with only 7% reduction in degradation of feed DM. However, higher CT inclusions, while further reducing CH4 emissions, have substantive negative effects on DM digestibility.