Comparative trace mineral nutritional balance of first-litter gilts under two dietary levels of copper intake.J Trace Elem Med Biol 1995; 9(2):102-11JT
Seven pairs of purebred Landrace first-litter gilts, housed in individual stainless-steel metabolic cages were used in this study. A low-Cu (LCu) basal diet containing only 2 mg/kg of Cu was compared to the control (CCu) diet, which was supplemented with cupric carbonate to provide 10 mg/kg of Cu. Both diets were fed at the rate of 2 kg per day to first-litter gilts during the entire pregnancy. The metabolic response under these two levels of dietary Cu intake was evaluated through nutritional balances conducted for 5 days starting at 30, 60 and 100 days of pregnancy. Total urine collection was done through teflon-coated catheters to the bladder while daily fecal collection was carried out continuously. Water consumption was measured and periodic samples were collected for analysis. Nutritional balances included DM digestibility, Cu, Zn, Fe and Mn. The LCh group consumed 4.26 mg of Cu per day while the CCu received 25 mg of Cu per day. This includes 1 mg per day in the drinking water in both groups. DM digestibility was significantly (P < 0.05) higher during early pregnancy in the LCu group compared to the CCu group, which showed a significant (P < 0.05) increase in DM digestibility from early to late pregnancy period. Dietary Cu intake had a direct effect (p < 0.05) on Cu balance but also altered the Zn and Fe nutritional balance, leaving Mn balance almost unchanged. Feces represented the almost exclusive route of excretion of trace minerals. Regardless of the dietary Cu intake, it represents more than 99.9% of the Fe and Mn, 98% of the Zn and 97% of the Cu was excreted daily through feces plus urine. The nutritional balance of Cu, Zn and Fe, in absolute amounts as well as relative to the level of intake, improved significantly as pregnancy progressed. Although relative retention of the low-Cu group was significantly improved compared to the control group, the absolute amount was still much lower. The well recognized dietary and metabolic interactions of Cu with Zn and Fe were evident in the first-litter gilts receiving the low-Cu diet during pregnancy. The absolute amount, as well as the relative retention as a % of the intake, was increased on average during the entire pregnancy for Zn by more than 70% and for Fe by more than 80% during the last third of pregnancy. In contrast Mn balance was almost unchanged. The major response to low-Cu intake was directed toward greater apparent absorption of the trace minerals which was reflected in a reduced fecal excretion.