摘要Background During the weaning phase,piglets are exposed to significant physiological and environmental stress-ors,which disrupt the balance of their intestinal microbiota and often lead to severe diarrhea.Previous studies have demonstrated that alfalfa fiber,derived from the stems and leaves of alfalfa,can effectively alleviate diarrhea in piglets.Additionally,multiple studies have highlighted the potential of fecal microbiota transplantation(FMT)in mitigating diarrhea in various models of intestinal diseases in young animals.However,the specific mechanisms by which FMT from targeted sources alleviates diarrhea in weaned piglets remain to be fully elucidated.Results In this study,FMT from donor piglets fed an alfalfa fiber-supplemented diet effectively alleviated diarrhea,improved intestinal morphology,and enhanced gut barrier function in weaned piglets.FMT further promoted the col-onization of beneficial bacterial genera(including UCG-005,unclassified Lachnospiraceae,Lachnospiraceae AC2044 group,UCG-002,Candidatus Saccharimonas,and Lachnospiraceae ND3007 group)while inhibiting the detrimental genus Tyzzerella,consequently enhancing the production of short-chain fatty acids(SCFAs).Additionally,FMT upregu-lated riboflavin metabolism,leading to elevated flavin adenine dinucleotide(FAD)levels and increased glutathione reductase activity,thereby collectively attenuating lipopolysaccharide(LPS)-induced oxidative stress and contributing to intestinal health.Conclusions We found that FMT modulates the structure of the gut microbiota,enhances microbial diversity and composition,increases the production of SCFAs,and upregulates riboflavin metabolism to elevate FAD levels.These changes collectively enhance immune and antioxidant capacities,thereby alleviating diarrhea.