Microbial functional maturation in the GIT microbiota of goat kids from birth to rumination. A, PCoA of GIT functional potentials at the gene level based on bray–Curtis dissimilarity in the rumen, ileum and colon, respectively; B and C, temporal variation in abundances of CAZymes (amylase, cellulase, and hemicellulase), together with genes involved in glycolysis, production of SCFAs (acetate, propionate, and butyrate), and methanogenesis (H₂ + CO₂ and methylotrophic pathways); B presents the sum of each CAZyme category or metabolism pathway, while C presents key rate-limiting enzymes; D, graphical overview of early-life assembly trajectory of microbial composition, and carbohydrate metabolic cascades in the rumen and colon during goat development. All the abundances were expressed as transcripts per million (TPM).