Abstract
The gut microbiota plays a crucial role in maintaining swine health and understanding its stage-specific variations provides a scientific basis for health assessment. This study investigated the structural changes in intestinal microbiota during the development of Sichuan-Tibetan black pigs (n = 15) by collecting fecal samples at three growth stages: the nursery period (1 month), growing period (3 months), and finishing period (10 months). Microbial profiling was performed using 16S rRNA sequencing. Results showed no significant difference in the Shannon index between the nursery and growing periods, while the finishing period exhibited distinct ACE and Chao 1 indices compared to other stages. PCoA and NMDS analyses revealed significant structural divergence in the finishing period microbiota, with greater intra-group variability observed in the nursery and growing periods. At the phylum level, Firmicutes abundance increased progressively with growth, becoming the absolute dominant phylum, whereas Bacteroidota showed a declining trend. These characteristics are particularly prominent during the finishing period. At the family level, Lactobacillaceae abundance increased continuously. Oscillospiraceae remained stable during the early stages but decreased significantly in the finishing period. Genus-level analysis shows that Lactobacillus, especially L. amylovorus and L. reuteri, become dominant bacterial species during the finishing period. A total of 84 differentially abundant core microbiota were identified, with the finishing period containing the highest number. Functional annotation revealed 19 significantly different metabolic pathways across the three stages. The most significant is the enhanced activity of microorganisms during the finishing period in pathogen-related metabolism and exogenous degradation, reflecting their adaptability to complex feed. These findings demonstrate stage-dependent variations in the gut microbiota of Sichuan-Tibetan black pigs, providing valuable references for nutritional regulation and feeding management practices.