Effects of dietary zinc/copper ratios on the metabolism of zinc and copper in weaned pigs.

This study compared the effects of different dietary zinc/copper ratios on zinc (Zn) and copper (Cu) metabolism in weaned pigs. One hundred sixty piglets (7.81 ± 0.25 kg; 21 days of age) were used in a completely randomized 2x2 factorial design composed with high (H) and low (L) levels of added dietary Zn (100 and 3000 mg/kg) and dietary Cu (6 and 130 mg/kg). Piglets were slaughtered at 21, 28, 35 and 42 days of age for blood and tissues collection. Serum, jejunum mucosa , liver, and kidney concentrations of Zn and Cu were analyzed as well as tissues mRNA abundance of genes related to their metabolism. Serum and liver Zn concentrations increased at d28, 35 and 42 in HZn groups compared to pre-treatment levels (d21; P ≤ 0.01) but for LZn animals, values decreased at d28, 35 and 42 in liver (P ≤ 0.01) but remained stable vs d21 levels in serum (P ≥ 0.37). Serum, jejunum mucosa, liver, and kidney Zn concentrations were greater in HZn groups from d28 (P ≤ 0.01). In jejunum mucosa, the mRNA expression of ZIP4 was lower in HZn piglets at d28 (P ≤ 0.01) and at d42 whereas HCu supplementation increased ZIP4 expression in LZn but not in HZn diets (P = 0.05). For ZNT1, MT3 and MT1, values of relative mRNA expression were greater for HZn animals in jejunum mucosa, liver, and kidney (P ≤ 0.01) from d28. In kidney (P < 0.01) at d42, HZn supplementation increased MTs expression in both LCu or HCu groups. Serum and liver Cu concentrations decreased at d35 and 42 in all treatments compared to d21 (P ≤ 0.04), except LZnHCu in liver that was not different from d21 (P ≥ 0.17). Serum Cu concentrations were lower in HZn and greater in HCu groups at d35 and 42 (P ≤ 0.01) whereas hepatic Cu was reduced by HZn diets in both LCu and HCu groups at d35 and 42 (P ≤ 0.01). Jejunum Cu concentrations were increased by HCu diets in HZn but not in LZn groups at d28 and 42 (P ≤ 0.04). Renal Cu concentrations were greater in HZn groups at d28 (P < 0.01) whereas at d42 HZn diets increased Cu values in both LCu and HCu groups (P ≤ 0.01). The expression of ATP7A in kidney at d42 was greater for HZn groups (P = 0.02). In conclusion, high dietary Zn levels were not efficiently regulated by homeostatic mechanisms and significantly impaired Cu homeostasis. Low dietary Zn/Cu ratios allow a more efficient regulation of the metabolism of these trace minerals in post-weaning piglets. The current official recommendations for Zn and Cu to post-weaning piglets apparently do not fulfil their requirements.