Methane production from in vitro incubation of kikuyu grass, lucerne and forages containing condensed tannins

Abstract

A series of in vitro incubations with kikuyu grass (Pennisetum clandestinum), lucerne and six legumes containing condensed tannins (CT) were undertaken to evaluate this technique against in vivo trials in New Zealand, measuring methane emissions. Published trials have demonstrated a reduction in methane emissions associated with CT and in one instance from kikuyu. The incubations used fresh minced forage (equivalent to 0.5 g dry matter (DM)) and were carried out in 50 ml sealed bottles containing buffer and rumen inoculum. Gas was sampled through a septum to monitor volume and composition throughout the 24h incubation. Incubation for 24 h resulted in 2.4-6.6 % conversion of DM to methane, and suggested CT concentrations below about 8% of the DM can reduce methane production without inhibiting fermentation rate. Higher concentrations of CT (> 8%) were associated with a lower rate of digestion. In common with in vivo trials, CT concentration in forage DM was inversely related to methane (adjusted R2 = 0.49; P = 0.01) and volatile fatty acid (adjusted R2=0.86; P<0.001) production. Ash concentration in forage DM was proportionally related to methane (adjusted R2=0.56; P=0.005). Keywords: ash, condensed tannins, in vitro incubation, methane, rumen