Cold Exposure Shifts Gut Microbial Butyrate Synthesis Toward the Lysine-Dependent and But-Mediated Terminal Pathways to Enhance Cold Tolerance in Min Pigs

This study combined seasonal observation in Min pigs and acute cold challenge experiments in Min pigs and Large White pigs to analyze changes in gut butyrate synthesis under cold exposure and its association with thermogenesis. Compared with summer, Min pigs in winter showed significantly higher Bacteroidota abundance (p = 0.006), lysine-pathway genes (p < 0.05), and relative gene abundance of the but terminal pathway (p < 0.05). Fecal (47.96 vs. 40.24 µmol/L, p = 0.020) and serum (4.64 vs. 2.17 µmol/L, p = 0.046) butyrate were also elevated and correlated with 10 thermogenesis-related genes (p < 0.05). Acute cold challenge increased serum butyrate (p = 0.017) and SLC16A1 expression (adjusted p = 0.027) only in Min pigs. Min pigs exhibited higher lysine pathway abundance and greater but terminal contribution than Large White pigs. Metagenomic binning recovered 40 lysine-pathway MAGs (27 unique to Min pigs) and 15 dual-pathway MAGs (11 unique to Min pigs), with Bacteroidota MAGs harboring complete lysine and dual terminal pathways. Collectively, cold exposure correlates with enrichment of lysine-dependent and but terminal butyrate synthesis pathways, highlighting butyrate-producing bacteria as candidate taxa for further investigation of cold-induced gut metabolic remodeling in pigs.