Estimation of the relative bioavailability of zinc from inorganic zinc sources for sheep

Two experiments were conducted to study bioavailability of reagent (RG) and feed (FG) grade sources of Zn for sheep based on tissue Zn uptake and liver metallothionein (MT) concentration. In both experiments, 42 crossbred wether lambs were given a practical basal diet containing 44 mg kg−1 Zn (Exp. 1) or 64 mg kg−1 Zn (Exp. 2) for a 7 day adjustment period followed by experimental diets for 23 days. In Exp. 1, the basal diet was supplemented with 0, 700, 1400, or 2100 mg kg−1 Zn as RG ZnSO4 · 7H2O (standard) or 1400 mg kg−1 Zn as RG Zn basic carbonate, Zn oxide, or metallic Zn. Based on multiple linear regression slope ratios of log10 transformed accumulation of Zn in pancreas, liver and kidney on dietary Zn concentration, relative bioavailability estimates were sulfate 100, carbonate 106, oxide 106, and metal 76. In Exp. 2, added concentrations were the same and sources were FG sulfate-A (standard) or FG sulfate-B, oxide-A, and oxide-B. Bioavailability estimates on the same basis were 100, 86, 87, and 79 respectively. Use of liver MT as the response criterion gave estimates of 100, 88, 88, and 77 respectively.