Effects of high levels of zinc oxide and dietary zinc/copper ratios on the metabolism of iron in weaned pigs

Abstract The present study compares the use different levels of dietary zinc oxide and zinc/copper ratios on the metabolism of iron (Fe) in weaned pigs. Two experiments were conducted using 120 and 160 weanling piglets (7.96 ± 1.17 kg and 7.81 ± 0.25 kg body weight, respectively) that were randomly assigned to the experimental treatments. Experiment I: diets supplemented with 100, 1,000, and 3,000 mg/kg of zinc (Zn) as ZnO (LZn, MZn, HZn) and 130 mg/kg of copper (Cu) as CuSO4; experiment II: diets supplemented with 100 or 3,000 mg/kg of Zn as ZnO (LZn and HZn) in combination with 6 or 130 mg/kg of Cu as CuSO4 (LCu and HCu). In both experiments, diets had similar levels of supplemental Fe (100 mg/kg of Fe as FeSO4). Piglets were slaughtered at d21 (weaning), d23 (experiment I), d28 (experiment II), d35, and d42 to assess whole blood, serum, and liver Fe concentrations, hemoglobin concentration, and the relative expression of key genes associated with Fe metabolism in jejunum and liver. Whole blood Fe and hemoglobin concentrations (experiment I) as well as serum Fe concentrations (experiments I and II) were not affected by dietary treatments (P ≥ 0.11). Liver Fe concentrations (experiment II) and total liver Fe content (experiments I and II) were lower (P ≤ 0.05) in HZn compared to LZn groups at d42. In both experiments, the mRNA expression of jejunal DMT1 was lowest and that of jejunal FTH1 was highest at d42 (P ≤ 0.04) for HZn piglets. In experiment II only, jejunal FTH1 and FPN1 expression were greater (P ≤ 0.04) in HCu compared to LCu groups at d42. The highest expression of hepatic FTH1 and FPN1 at d35 and d42 (P ≤ 0.02) was detected in HZn piglets in both experiments. For hepatic HAMP, expression values were greater (P = 0.04) at d42 in HZn groups. In conclusion, high dietary ZnO levels impair Fe metabolism but the effects are not intense enough to impact circulating Fe and hemoglobin concentrations.