Combination of methane-inhibitors and hydrogen-acceptors: effects on <i>in vitro</i> rumen fermentation

Methanogenesis inhibition in vivo is often associated with higher dihydrogen (H2) emission without an increase in production efficiency. The objectives of this in vitro study were to test the effects of the addition of iodoform (IOD; 0.007% w/w on DM basis) and quercetin (QUE; 3%) as CH4-inhibitors, and activated charcoal powder (ACP; 3%), phloroglucinol (PHL; 5%), and vitamin E (VitE; 0.45%) as H2-acceptors on CH4 and H2 productions and rumen fermentation. The additives were tested alone, as combination of each CH4-inhibitor with a H2-acceptor, or as combination of both CH4-inhibitors with each H2-acceptor against the basal feed without additives (CTR). Fermentations lasted 48 h, total gas production was determined by AnkomRF system equipped with gasbags. Gas samples were taken at 24 h to analyse the production of CH4 and H2. After 48 h, pH and concentrations of volatile fatty acids (VFA) and ammonia were determined. Compared to CTR, IOD reduced CH4 production (mL/g DM) by 62.0% and increased H2 production, while QUE induced a not significant −19.3% without affecting H2 production. All the H2-acceptors failed to reduce H2 production when tested in combination with the CH4-inhibitors. Phloroglucinol increased VFA concentration without affecting CH4 production, ACP acted as IOD antagonist, while VitE had no impact on almost all the parameters considered when incubated alone or in combination with the CH4-inhibitors. Finally, a synergistic effect was observed with the combined use of IOD and QUE, which significantly reduced CH4 production (−97.6% vs CTR), minimising the H2 increase without negative effects on VFA concentration.