Chemical characteristics and relative bioavailability of supplemental organic zinc sources for poultry and ruminants

Eight commercially available organic Zn products and reagent-grade ZnSO4. 7 H(2)O (Zn Sulf) were evaluated by polarographic analysis, and solubility in .1M K2HPO4-KH2PO4 buffer (pH 5), .2 M HCl-KCl buffer (pH 2), and deionized water. Fractions from these solubility tests were evaluated by gel filtrat ion chromatography for structural integrity. Degree of chelation was genera lly positively related to chelation effectiveness determined by polarograph y. The organic sources were Zn methionine complex A (Zn MetA), Zn methionin e complex B (Zn MetB), Zn polysaccharide complex (Zn Poly), Zn lysine compl ex (Zn Lys), Zn amino acid chelate (Zn AA), Zn proteinate A (Zn ProA), Zn p roteinate B (Zn ProB), and Zn proteinate C (Zn ProC). Three experiments wer e conducted to estimate the relative bioavailability of Zn from the organic Zn supplements for chicks and lambs when added at high dietary levels to p ractical diets. Bone Zn concentration increased (P < .001) as dietary Zn in creased in both experiments. When Zn Sulf was assigned a value of 100% as t he standard, multiple linear regression slope ratios of bone Zn from chicks fed 3 wk regressed on dietary Zn intake gave estimated relative bioavailab ility values of 83 +/- 14.6 and 139 +/- 16.9 for Zn AA and Zn ProA, respect ively, in Exp. 1 and 94 +/- 11.6, 99 +/- 8.8, and 108 +/- 11.4 for Zn Poly, Zn ProB, and Zn ProC, respectively, in Exp. 2. In Exp. 3, 42 lambs were fe d diets containing Zn Sulf, Zn ProA, Zn AA, or Zn MetB for 21 d, Based on m ultiple linear regression slope ratios of liver, kidney, and pancreas Zn an d liver metallothionein concentrations on added dietary Zn, bioavailability estimates relative to 100% for Zn Sulf were 130, 110, and 113 for Zn ProA, Zn AA, and Zn MetB, respectively. Except for Zn ProA, which was greater, t he organic Zn supplements had bioavailability values similar to that of Zn Sulf for chicks and lambs. Bioavailability of organic Zn products was inver sely related to solubility of Zn in pH 5 buffer in chicks (r(2) = .91) and pH 2 buffer in lambs (r(2) = .91), but not to an estimate of degree of chel ation.