摘要Background Weaning stress-induced diarrhea is widely recognized as being associated with gut microbiota dysbio-sis.However,it has been challenging to clarify which specific intestinal microbiota and their metabolites play a crucial role in the antidiarrhea process of weaned piglets.Results In this study,we first observed that piglets with diarrhea exhibited a lower average daily gain and higher diarrhea score,and elevated levels of lipopolysaccharide(LPS)and D-lactate(D-LA)compared to healthy piglets.Subsequently,we analyzed the differences in intestinal microbial composition and metabolite levels between healthy and diarrheal weaned piglets.Diarrheal piglets demonstrated intestinal microbiota dysbiosis,characterized pri-marily by a higher Firmicutes to Bacteroidota ratio,a deficiency of Lactobacillus amylovorus and Lactobacillus reuteri,and an increased abundance of Bacteroides sp.HF-5287and Bacteroides thetaiotaomicron.Functional pro-filing of the gut microbiota based on Kyoto Encyclopedia of Genes and Genomes(KEGG)data was performed,and the results showed that tryptophan metabolism was the most significantly inhibited pathway in piglets with diar-rhea.Most tryptophan metabolites were detected at lower concentrations in diarrheal piglets than in healthy piglets.Furthermore,we explored the effects of dietary indole-3-aldehyde(Iald),a key tryptophan metabolite,on intestinal development and gut barrier function in weaned piglets.Supplementation with 100 mg/kg Iald in the diet increased the small intestine index and improved intestinal barrier function by promoting intestinal stem cell(ISC)expansion in piglets.The promotion of ISC expansion by Iald was also confirmed in porcine intestinal organoids.Conclusions These findings revealed that intestinal microbial tryptophan metabolite Iald alleviates impaired intesti-nal development by promoting ISC expansion in weaned piglets.