High-concentrate diets commonly used in finishing beef cattle can impair colonic health by disrupting the intestinal barrier, promoting inflammation, oxidative stress, and electrolyte imbalances. This study aimed to evaluate the effects of alkaline mineral ion complex (AMC) supplementation on colonic health in cattle under high-concentrate feeding conditions. Results demonstrated that AMC supplementation significantly enhanced colonic barrier integrity by upregulating tight junction proteins and increasing goblet cell numbers, thereby improving mucosal defense. AMC also mitigated inflammatory cytokines (IL-1β, IL-6) and oxidative stress (reduced MDA and increased GSH-Px). Additionally, AMC supplementation restored electrolyte balance by enhancing Na⁺, K⁺, and Ca reabsorption, likely through upregulation of ion transporters and improvement of intestinal barrier function. The microbial ecosystem was also reshaped by AMC, with increased α-diversity and a reduction in pathogenic bacterial populations. Metabolomic and proteomic analyses revealed the downregulation of sphingolipid signaling pathway, particularly sphingosine, and the modulation of BCAA degradation pathways. These metabolic shifts suggest reduced inflammation and improved epithelial function. Collectively, AMC supplementation offers a promising dietary intervention to restore gut homeostasis, reduce inflammation, and enhance colonic health under high-concentrate feeding conditions.