**Background:** Piglets are prone to iron deficiency anemia due to low iron stores at birth, inadequate sow milk supply, and rapid growth. While various iron supplementation strategies exist, data on the effects of organic Fe-peptide chelating complexes on iron uptake and transport in piglets are limited. This study aimed to evaluate the effects of replacing inorganic iron with an organic Fe-peptide complex on growth performance, hematological parameters, iron status, enzyme activities, and gene expression related to iron homeostasis in weaned pigs.
**Methods:** A total of 480 weaned pigs (Duroc X Landrace, 28 d old, 8.14 ± 0.71 kg) were allotted to four treatments (30 pigs/pen, 4 replicate pens/treatment) for 42 days (d 28 to d 70). The treatments were: 1) control basal diet (Con, 75.8 mg Fe/kg), 2) Con + 150 mg Fe/kg as inorganic Fe (iFe), 3) Con + 75 mg Fe/kg as inorganic Fe + 75 mg Fe/kg as organic Fe-peptide complex (iFe+oFe), and 4) Con + 150 mg Fe/kg as organic Fe-peptide complex (oFe). Growth performance (ADG, ADFI, F/G) was measured. Blood samples were collected on d 28, 42, 56, and 70 for hemoglobin and MCHC analysis. At d 70, pigs were sacrificed, and liver, kidney, and spleen samples were collected for iron content and CAT and SDH activity analysis. Liver and bone marrow samples were collected for gene expression analysis of Ferritin, Tf, TfR1, and NCOA4. Data were analyzed by one-way ANOVA with significance set at P ≤ 0.05.
**Key Results:** No significant differences (P > 0.05) were observed in final body weight, ADG, ADFI, F/G, hemoglobin, or MCHC between any groups. However, all Fe-supplemented groups had significantly greater iron concentrations in the liver, kidney, and spleen compared to the control (P < 0.05). The oFe group had significantly greater tissue iron concentrations than the iFe or iFe+oFe groups (P < 0.05). For example, liver iron content was 147.8 ± 23.4 mg/kg (Con), 238.7 ± 13.8 mg/kg (iFe), 285.8 ± 19.9 mg/kg (iFe+oFe), and 398.6 ± 12.4 mg/kg (oFe) (P < 0.0001). The oFe group also showed significantly greater CAT and SDH activities in the liver (CAT: 89.0 ± 4.7 U/mg protein; SDH: 99.9 ± 4.6 U/mg protein) compared to the Con group (CAT: 74.8 ± 3.2 U/mg protein; SDH: 82.8 ± 1.3 U/mg protein) (P < 0.05). In the kidney, only the oFe group had significantly higher CAT and SDH activities than the Con group (P < 0.05). No differences in CAT and SDH activities were observed in the spleen. Dietary iron supplementation increased NCOA4 mRNA expression and decreased TfR1 mRNA expression in the liver (P < 0.05). In bone marrow, TfR1, NCOA4, and Ferritin mRNA expressions were greater in the iFe and iFe+oFe groups compared to the control and oFe groups (P < 0.05).
**Clinical Implications:** This study demonstrates that while growth performance and standard hematological parameters are insensitive indicators of iron status in weaned pigs fed a commercial corn-soybean meal diet, tissue iron content and Fe-containing enzyme activities are more sensitive biomarkers. The organic Fe-peptide complex (oFe) showed superior bioavailability compared to inorganic iron, leading to higher iron accumulation in tissues and greater activity of iron-dependent enzymes. The differential gene expression patterns, particularly the involvement of the NCOA4-ferritin axis, suggest that organic Fe-peptide complexes may modulate intracellular iron homeostasis differently than inorganic sources. These findings support the use of organic Fe-peptide complexes as a more effective iron supplementation strategy for weaned pigs, potentially reducing the risk of iron deficiency anemia in modern, fast-growing pig production systems.