Gallic and Ellagic\nAcids Differentially Affect Microbial\nCommunity Structures and Methane Emission When Using a Rumen Simulation\nTechnique

Dietary tannins can\naffect rumen microbiota and enteric\nfermentation\nto mitigate methane emissions, although such effects have not yet\nbeen fully elucidated. We tested two subunits of hydrolyzable tannins\nnamed gallic acid (GA) and ellagic acid (EA), alone (75 mg/g DM each)\nor combined (150 mg/g DM in total), using the Rusitec system. EA and\nEA+GA treatments decreased methane production, volatile fatty acids,\nnutrient degradation, relative abundance of Butyrivibrio\nfibrisolvens, Fibrobacter succinogenes, Ruminococcus flavefaciens but increased Selenomonas ruminantium. EA and EA+GA increased urolithins\nA and B. Also, EA and EA+GA reduced bacterial richness, with limited\neffects on archaeal richness. For bacteria, Megasphaera\nelsdenii was more abundant after EA and EA+GA, while\nMethanomethylophilaceae dominated archaea in all treatments. EA was\nmore effective than GA in altering rumen microbiota and fermentation\nbut GA did not reduce VFA and nutrient degradation. Thus, dietary\nsupplementation of EA-plant extracts for ruminants may be considered\nto mitigate enteric methane, although a suitable dosage must be ensured\nto minimize the negative effects on fermentation.