Effects of supranutritional levels of dietary zinc oxide on zinc, copper, and iron metabolism in post-weaned pigs

This study evaluated the impact of supranutritional levels of dietary zinc oxide (ZnO) on zinc (Zn), copper (Cu), and iron (Fe) homeostasis in post-weaned pigs. One hundred twenty piglets were selected at d14 of age (5.65 ± 0.68 kg). At weaning (d21), they were fed a basal post-weaning diet (without antibiotics) supplemented (n = 40/treatment) with 100 mg/kg (low; LZn), 1000 mg/kg (medium; MZn) or 3000 mg/kg (high; HZn) of ZnO until d42. Dietary levels of Cu (130 mg/kg) and Fe (260 mg/kg) remained constant throughout the experimental period. Piglets were sacrificed at d21, d23, d35, and d42 of age (n = 10/treatment/d) for samples collection. Serum concentrations and total liver content of Zn and Cu were not different among treatments on d21 and d23 (P ≥ 0.10). For Zn, treatment effects were detected at d35 and d42 (P < 0.01) on both serum concentration and total Zn content in liver. For both parameters, values were greatest for HZn, intermediary for MZn, and lowest for LZn irrespective of ages in the two periods. For Cu, treatment effects were detected at d35 and d42 (P < 0.01) on both serum concentration and total Cu content in liver. For both parameters, values were greatest for LZn and MZn and lowest for HZn irrespective of ages. For Fe, no treatment effect was detected either on whole blood Fe concentrations (P = 0.81) or hemoglobin levels (P = 0.76). However, for total Fe content in liver, treatment effects were detected (P < 0.01). Values were greatest for LZn and lowest for HZn at d35 and d42 whereas for MZn they were intermediary at d35 and similar to LZn at d42 (P ≤ 0.01). In conclusion, supranutritional levels of dietary ZnO fed to piglets during 3 weeks post-weaning significantly impacted Zn, Cu, and Fe homeostasis. These results emphasise the potential risk of Cu deficiency as well as impairment in building body Fe reserves under long-term supranutritional supplementation of ZnO.