Effects of L-threonine supplementation on growth performance, intestinal histology, gut microbiota and gene expression related to gut barrier function in broiler chickens.

L-threonine (Thr) facilitates gut barrier restoration, yet its coordinated link with gut microbiota and intestinal barrier-related genes remains unclear. This study assessed the effects of drinking-water Thr supplementation (0, 150, 300, 600 mg/kg BW) on growth performance, jejunal morphology, cecal microbiota and transcriptional profiles in 120 one-day-old broilers during a 21-day trial. The results showed that medium and high doses of Thr increased body weight, and the 300 mg/kg group exhibited a lower feed conversion ratio along with improved jejunal villus height (VH), crypt depth (CD) and villus height to crypt depth ratio (VCR). 16S rRNA sequencing revealed that moderate Thr supplementation promoted greater cecal microbial richness and diversity, an elevated Firmicutes/Bacteroidetes ratio, and the enrichment of short-chain fatty acid (SCFA)-producing genera such as Mediterraneibacter, Faecalibacterium and Ruminococcus. Furthermore, transcriptome sequencing explored potential molecular mechanisms, identifying differentially expressed genes (DEGs) enriched in cell adhesion and PI3K/Akt immune-inflammatory pathways. Validation of mRNA and protein levels indicated that Thr upregulated tight junction proteins and reduced pro-inflammatory cytokines. Multi-omics correlation analysis proposed a Thr-microbiota-key gene regulatory axis, suggesting that Thr synergistically alleviates intestinal inflammation and maintains gut structural integrity. In summary, 300 mg/kg Thr supplementation modulates cecal microbiota and regulates expression of barrier and inflammatory genes, thereby improving jejunal morphology and growth performance of broiler chickens.