RELATIVE BIOAVAILABILITY OF 2 ORGANIC AND 2 INORGANIC ZINC SOURCES FED TO SHEEP

A study was conducted to compare supplemental Zn lysine (ZnLys), Zn methionine (ZnMet), ZnSO4, and ZnO on Zn, Cu, and metallothionein (MT) concentrations in various fluids and tissues of 40 wether lambs. Supplemental Zn (360 mg/kg) was fed for 3 wk, withdrawn for 4 wk, and then resumed for another week. Mineral (Zn and Cu) concentrations were determined in serum, liver, pancreas, kidney, bone, bone marrow, hoof, and leg muscle, and only Zn was determined in skin and cornea. Metallothionein concentration was determined in liver, pancreas, and kidney. By d 49 serum Zn had increased less (P < .05) for controls than for all lambs except those fed ZnMet, and on d 55 it had increased more (P < .05) for ZnLys than for all but ZnSO4. There were no treatment effects in serum Cu concentration, but overall Cu concentration fell slightly for all treatments from d 0. The ZnLys-treated lambs had the highest (P < .05) Zn accumulation (581, 389, and 340 mg/kg) in kidney, liver, and pancreas, respectively. Both ZnSO4- and ZnMet-treated lambs had higher (P < .05) liver Zn concentrations (195 and 198 mg/kg, respectively) than the control lambs (127 mg/kg). Mean Zn concentration of bone, bone marrow, cornea, skin, hoof, and muscle was not different (P > .05) for lambs among treatments. The ZnLys-treated lambs had the highest (P < .05) MT concentrations (79, 167, and 68 mu g MT/g for liver, kidney, and pancreas, respectively). Mean muscle Cu concentration was highest (P < .05) for controls (10 mg/kg). Organic sources of Zn have equal or greater availability than the most available inorganic source and may be metabolized differently in some tissues.