In this study, RuCel143, an acidophilic GH5 cellulase endowed with β-glucanase and xylanase activity was identified from the rumen metagenome. Its hydrolytic efficacy was evaluated using barley in an in vitro simulation of monogastric digestion. Optimal activity for RuCel143's cellulase was observed at pH 3.5 and 40 °C, while for xylanase it was pH 4.0 and 50 °C. The cellulase exhibited strong pH tolerance, retaining 94.3 % of its initial activity after 4 h at pH 2.5. In contrast, xylanase activity increased by 80.7 % after 4 h at pH 8.0. RuCel143 exhibited good resistance to various ions and common inhibitors, with Cu