High dietary levels of zinc oxide modulate the metabolism of trace minerals and may be detrimental to post-weaning piglet health

Despite environmental and public health (bacterial resistance) issues, supranutritional levels of zinc oxide (ZnO) are still commonly used to prevent diarrhea in post-weaning piglets. In Canada, these levels represent more than eight-fold the CFIA proposed maximum levels at 300 mg/kg. The limited knowledge of their consequences for the metabolism of trace minerals has hampered the replacement of this strategy without compromising piglet health. Our laboratory has performed a series of studies to better understand the impact of dietary Zn levels on trace minerals metabolism. In a bioavailability study, Zn concentrations of 200 mg/kg impaired Cu (20 mg/kg) intestinal absorption whereas in a metabolism study using supplemental Zn at 100, 1000, 3000 mg/kg and Cu at 130 mg/kg, Zn provision at 3000 mg/kg as ZnO was inadequately regulated by the organism with the potential induction of Cu and Fe deficiency under long-term supplementation during the post-weaning period. These results indicated that optimal dietary ratios among these minerals are needed to improve their homeostasis, and this was confirmed in another bioavailability study where a Zn/Cu ratio of 15:1, within nutritional levels, optimized the absorption of Zn and Cu. In a long-term metabolism study using different dietary Zn/Cu ratios (3000/130, 3000/6, 100/130, 100/6), the risk of Cu deficiency described above was confirmed and lower dietary Zn/Cu ratios were shown to optimize Cu without compromising Zn metabolism. In conclusion, dietary ZnO levels have a major contribution in modulating the metabolism of Zn, Cu, and Fe in post-weaning piglets, with potential detrimental health effects.

Keywords: copper, iron, metabolism, pig, zinc.