Dietary ferrous glycinate supplementation reshapes the gut microbiota and improves intestinal barrier function in weaned piglets by reducing luminal iron accumulation.

Non-absorbed inorganic iron in the digestive tract can be directly utilized by microorganisms, particularly pathogens. This study aimed to evaluate the feasibility of substituting ferrous sulfate (FeSO₄) with lower doses of ferrous glycinate (Fe-Gly) in weaned piglets. A total of 30 weaned piglets were randomly assigned to three dietary treatments (n = 10): a Control group, a Gly-Fe-50 group (50 mg/kg Fe-Gly), and a Gly-Fe-75 group (75 mg/kg Fe-Gly). Compared with 100 mg/kg FeSO₄, supplementation with 50 or 75 mg/kg Fe-Gly did not significantly affect growth performance parameters, indicating that Fe-Gly maintained comparable growth performance at a 25-50% lower inclusion level. Numerically, 50 mg/kg Fe-Gly showed higher ADFI and ADG, although these differences were not statistically significant. Fe-Gly supplementation was associated with improvements in intestinal barrier function in weaned piglets. Furthermore, Fe-Gly supplementation significantly elevated serum total iron-binding capacity (TIBC) (p < 0.05), indicating enhanced iron transport efficiency. Gene expression and microbial sequencing analyses revealed that Fe-Gly upregulated antioxidant genes (SLC7A11, P62) in the jejunum. Additionally, it significantly augmented the proportion of beneficial microbes, such as Lactobacillus and Akkermansia, while reducing the proportion of Proteobacteria and Escherichia-Shigella. In summary, because of its high bioavailability, 50 mg/kg Fe-Gly does more than meet the growth and metabolic demands of piglets; it also reduces iron accumulation in the hindgut lumen. This mechanism restricts iron availability for intestinal pathogens, inhibiting their proliferation and thereby improving intestinal health in piglets.