Zinc kinetics in weaned piglets fed marginal zinc intake: Compartmental analysis of stable isotopic data

Kinetics of zinc metabolism are described for weanling piglets fed casein-based diets that contained 12–14 (marginal) or 100–104 (recommended) mg Zn/kg. After 10–11 days 61Zn was given to each animal intravenously as a bolus dose of 4 μg/kg body weight. Anticoagulated blood was withdrawn at timed intervals until 1, 24, or 120–144 h after label administration in short, intermediate, and long-term studies, respectively, at which times piglets were euthanized and liver, spleen, and kidney were excised. Zinc concentrations of diets, erythrocytes, plasma, spleen, liver, and kidney were determined by atomic absorption spectrophotometry, and 70Zn/61Zn was measured by inductively coupled plasma mass spectrometry. Data for label enrichments and total zinc content at all time points were fitted simultaneously for both dietary treatments by modification of a compartmental model previously developed for zinc metabolism in adult humans. Mean plasma and liver zinc concentrations were significantly lower (24% and 76%, respectively) in the marginal dietary group. Adjustments in values of model parameters that gave the best fit for the marginal group relative to the recommended group were 1) 5.52-fold higher fractional zinc absorption; 2) 30% lower release of zinc from erythrocytes; and 3) spleen accounting for a larger fraction (30% vs. 20%) of a smaller compartment that turns over in 3.6 h. Normal piglets compensate for marginal zinc intake primarily through increase in fractional zinc absorption. Differences in liver and plasma zinc caused by difference in dietary zinc correspond with calculations of their zinc pool sizes.