摘要Background Sustainable livestock production is essential for food security and environmental management.Lignocellulosic biomass can be used in animal feed,thereby reducing feed production costs and enhancing sustain-ability.Expansin-like proteins(ELPs)play essential roles in plant cell wall degradation,yet their functions remain largely underexplored in rumen microbes.The purpose of this study was to investigate the effects of rumen microbial ELPs on lignocellulose degradation.Results This study systematically identified 396 ELPs within the rumen microbiota,uncovering remarkable diver-sity,particularly among anaerobic fungi.Three representative ELPs from Pecoramyces ruminantium F1(PFLoos_1,PFSWO1_1,PFSWO2_1)were selected for biochemical characterization.While PFSWO2_1 could not be expressed,PFLoos_1 andPFSWO1_1 exhibited significant synergy with cellulases.The CBM10-containing PFSWO1_1 dem-onstrated superior thermal stability(up to 65 ℃)and substrate affinity,increasing rice straw hydrolysis efficiency by 21.6％(reducing sugar yield)compared to cellulase alone.Structural analyses revealed that CBM10 enabled PFSWO1_1 to preferentially bind complex substrates,whereas the single-domain PFLoos_1 targeted simpler sub-strates.Notably,ELP pretreatment of corn stover significantly improved fermentation quality(pH and lactic acid)and nutritional value(neutral detergent fiber,acid detergent fiber,and water-soluble carbohydrates).Conclusions These findings indicate that ELPs are abundant in the rumen and play a synergistic role in lignocellu-losic biomass conversion.