Background: This study aimed to compare three cotton-stalk processing strategies—grinding (FS), steam explosion (PH), and microbial fermentation (FJ)—and to clarify whether fermented cotton stalks preserve colonic epithelial integrity through a microbiota–metabolite–NF‑κB/MLCK axis in Hu sheep. Methods: Fifteen clinically healthy Hu sheep (26.7 ± 1.76 kg body weight; 115 ± 4 days of age) were used after a 14‑day adaptation period and randomly assigned to one of three diets ( n = 5 per treatment) containing 40% processed cotton stalks (FS, PH, or FJ) for 8 weeks. Results: PH and FJ increased final body weight compared with FS, and average daily gain increased progressively from FS to PH to FJ (206.07, 282.50, and 322.14 g/d, respectively; p < 0.05). Colonic fermentation profiles were markedly improved by FJ, evidenced by lower pH, ammonia nitrogen, free gossypol, and acetate ( p < 0.05), alongside higher total VFAs with elevated propionate and butyrate ( p < 0.05), whereas LPS was not different among treatments ( p > 0.05). Histology and scanning electron microscopy indicated that FJ maintained intact crypt architecture and epithelial surface continuity, while FS exhibited epithelial detachment and surface erosion. Metagenomic analysis revealed distinct community structures among groups, with FJ showing higher richness and enrichment of taxa associated with carbohydrate utilization and butyrate‑producing guilds (e.g., Lachnospiraceae ‑related genera such as Anaerostipes , Blautia , and Coprococcus ). Consistently, FJ suppressed colonic mucosal inflammation, as reflected by reduced IL‑1β, IL‑6, IL‑8, and TNF- α at both mRNA and protein levels ( p < 0.05). Mechanistically, FJ attenuated NF‑κB activation and downstream MLCK signaling, shown by decreased p‑p65/p65, p‑IκB/IκB, MLCK abundance, and p‑MLC/MLC ratio ( p < 0.05), while upregulating tight‑junction proteins (ZO‑1, occludin, claudin‑1, and claudin‑4; ( p < 0.05). Conclusion: Fermentation‑based processing of cotton stalks enhanced growth performance and promoted a favorable hindgut fermentation and microbial–metabolic milieu, thereby reinforcing colonic barrier integrity via inhibition of NF‑κB/MLCK‑associated inflammatory signaling, supporting fermented cotton stalk as a practical strategy to valorize cotton residues for ruminant feeding while mitigating gossypol‑related hindgut stress.