Bioavailability of zinc in several sources of zinc oxide, zinc sulfate, and zinc metal

zinc depletion-repletion assays were carried out with chicks to determine Z n bioavailability in five sources of ZnO, three sources of ZnSO4. H2O, and two sources of Zn metal. A standard 23% CP corn-soybean meal diet was fed d uring the first 3 d posthatching, after which it was replaced with a Zn-def icient soy concentrate diet (13.5 mg Zn/kg) until d 7. On d 8 after an over night period of feed withdrawal, chicks were fed for 12 d the Zn-deficient basal diet containing 0, 4.76, and 9.90 (Assay 1); 0, 5.06, or 10.12 (Assay 2); or 0, 4.73, or 9.13 (Assay 3) mg/kg supplemental Zn from analytical gr ade (AG) ZnSO4. 7H(2)O (22.7% Zn) to generate a standard response curve. Th e AG and feed-grade (FG) Zn sources being evaluated were then provided at a level that would fall within the standard curve. Weight gain (Assays 1, 2, and 3) and total tibia Zn (Assay 1) responded linearly (P < .01) to Zn sup plementation from ZnSO4. 7H(2)O. Weight gain regressed on supplemental Zn i ntake gave standard-curve equations with fits (r(2)) ranging from .94 to .9 7. In Assay 1, regression of total tibia Zn (Y, in micrograms) on supplemen tal Zn intake (X, in milligrams/12 d) gave the equation Y = 13.2 + 6.74 X ( r(2) = .90). Standard-curve methodology was used to estimate relative Zn bi oavailability (RBV), with REV of Zn in the ZnSO4. 7H(2)O standard set at 10 0%. Four sources of FG ZnO were evaluated: Source 1 (78.1% Zn, hydrosulfide process, U.S.), Source 2 (74.1% Zn, Waelz process, Mexico), Source 3 (69.4 % Zn, China), and Source 4 (78.0% Zn, French process, Mexico). Analytical-g rade ZnO (80.3% Zn) was also evaluated. Feed-grade ZnO Sources 1 and 4 as w ell as AG ZnO produced average REV values that were not different (P > .10) from the standard, but average REV values for FG Source 2 and FG Source 3 were only 34 (P < .05) and 46% (P < .05), respectively. All sources of ZnSO 4. H2O, which included two FG sources (source 1, 36.5% Zn; source 2, 35.3% Zn) and one food-grade source (36.5% Zn), were not different (P > .10) in R EV from the ZnSO4. 7H(2)O standard. Two Zn metal products, Zn metal dust (1 00% Zn) and Zn metal fume (91.5% Zn), were also evaluated, and they were fo und to have Zn REV values of 67 (P < .05) and 36% (P < .05), respectively. Feed-grade sources of ZnO vary widely in color, texture, Zn content, and Zn bioavailability.