This study aimed to investigate the effects of dietary tea polyphenols (TPs) supplementation on growth performance and meat quality. A total of 120 pigs ([Yorkshire × Landrace] × Duroc) aged 150 days with similar body weights (74.29 ± 0.55 kg), comprising equal numbers of females and castrated males, were randomly assigned to two treatments, each with three pens of 20 pigs: The Control group received a basal diet, and the TP group received the basal diet supplemented with 2000 mg/kg tea extract containing 15% TP. A 7-day adaptation preceded the 60-day feeding period. At the end of the experiment, the final bodyweight of the pigs was measured and six pigs per treatment were selected for sampling. The results showed that: (1) growth performance did not differ significantly, although feed-to-gain ratio and average daily feed intake were numerically lower in the TP group; (2) carcass weight, backfat thickness, and muscle alanine increased, whereas longissimus dorsi lightness and yellowness decreased (p < 0.05); (3) serum total superoxide dismutase and hepatic catalase and glutathione peroxidase activities increased (p < 0.05); (4) Chao1 richness and Shannon diversity were unchanged, and genus-level PCoA showed partial but non-significant separation of the colonic microbial communities (R = 0.1685, p = 0.090). Nevertheless, TP supplementation selectively altered specific bacterial taxa, with lower relative abundances of Pseudomonadota, Escherichia–Shigella, and Ligilactobacillus and higher relative abundances of Solobacterium, norank_f__p-2534-18B5_gut_group, and [Ruminococcus]_gauvreauii_group; and (5) Catenisphaera was positively correlated with serum total superoxide dismutase activity (p < 0.01), whereas the TP-enriched norank_f__p-2534-18B5_gut_group was positively correlated with muscle alanine content (p < 0.05). This study demonstrates concurrent antioxidant, meat-quality, and microbial responses to a TP-containing diet, supporting mechanistic research on a potential gut–liver–muscle association and refinement of supplementation strategies that balance antioxidant benefits with carcass fat deposition.

Background: The early-life gut microbiota plays a critical role in programming intestinal barrier function and immune homeostasis, with profound implications for long-term host health. However, the effects of early-life compound probiotic intervention on the maturation of intestinal barrier function and the underlying molecular mechanisms remain incompletely understood, particularly in large-animal models relevant to human physiology. Methods: In this preclinical study, 3627 neonatal piglets—a well-established translational model for human infant gut development—were orally administered a novel compound probiotic formulation comprising Bifidobacterium longum subsp. infantis BZ, Lactobacillus plantarum LZ, and Pediococcus acidilactici PZ during early life. A total of 1512 fecal samples collected at seven time points from birth to day 180 were analyzed by 16S rRNA sequencing, and 525 samples from three developmental windows (days 10, 25, and 70) were subjected to LC-MS-based metabolomics. The candidate metabolite indole-3-lactic acid (ILA) was further mechanistically validated in a DSS-induced colitis mouse model and in IPEC-J2 cells. Results: Early-life probiotic intervention significantly enhanced intestinal barrier integrity, as evidenced by improved intestinal morphology and upregulated expression of tight junction proteins—zonula occludens-1 (ZO-1), occludin (OCLN), and Claudin-1 (CLDN1)—in the jejunum (p < 0.05). Notably, intervention at birth was more effective than post-weaning administration, and two administrations (birth + weaning) yielded superior outcomes compared with a single administration (p < 0.05). Microbiome analysis revealed enhanced microbial diversity and enrichment of beneficial genera during the juvenile-to-adult transition (p < 0.05). Metabolomic profiling identified ILA as a signature metabolite consistently elevated by probiotic supplementation. Conclusions: These findings provide evidence that early-life compound probiotic intervention is associated with improved intestinal barrier maturation, with ILA identified as a key candidate metabolite that may mediate this effect, as supported by functional validation in murine and cellular models. This provides a mechanistic rationale for probiotic-based strategies to support intestinal health in human infants during critical developmental windows.