The bioavailability of zinc-methionine (ZnMET) was compared to that of feed-grade ZnSO4.H2O using three different diets: purified (crystalline amino acid [AA]), semipurified (soy isolate), and complex (corn-soybean [C-SBM]) diet. With the Zn-deficient purified or semipurified diet, weight gain and tibia Zn responded linearly to both ZnSO4.H2O and ZnMET supplementation. Common-intercept, multiple linear regression indicated differences in Zn bioavailability between ZnMET and ZnSO4.H2O for both diets as indicated by bone Zn. With the ZnSO4.H2O standard set at 100%, bioavailability of Zn from ZnMET was 117% (P less than .05) in the AA diet and 177% (P less than .01) in the soy isolate diet. The ZnMET was also compared to ZnSO4.H2O in a C-SBM diet containing 117 mg of Zn/kg. When high levels of Zn were added to this diet (0, 250, 500, and 750 mg/kg of supplemental Zn), consistent tissue Zn responses did not occur beyond the first increment. Addition of lower levels of supplemental Zn (0, 5, 10, 20, 30, 40 and 50 mg/kg) to a Zn-unsupplemented C-SBM basal diet (45 mg/kg of Zn), however, resulted in a broken-line, two-slope response in tibia Zn for both ZnMET and ZnSO4.H2O. Inflection points occurred at 60 and 54 mg of Zn/kg of diet for ZnSO4.H2O and ZnMET, respectively. The ratio of slopes (ZnMET:ZnSO4.H2O) below the inflection points was 206% (P less than .01), indicating that Zn was considerably more bioavailable in ZnMET than in ZnSO4.H2O for chicks consuming C-SBM diets. When feed-grade ZnO was compared to feed-grade ZnSO4.H2O in chicks consuming C-SBM diets, bone Zn slopes below the respective inflection points indicated that Zn was 61% bioavailable in ZnO relative to ZnSO4.H2O.

Based on zinc uptake in chick tibia, Zn bioavailability in cooked ground beef was equal to that of Zn in an inorganic standard (ZnSO4), whether Zn supplements were added to a soy-concentrate diet containing phytate or to a phytate-free egg-white diet. With both diet types, total tibia Zn was a linear (P < .01) function of supplemental Zn intake from ZnSO4, but the slope of the linear regression line was twice as great for the egg-white diet as for the soy-concentrate diet that contained phytate. At 10 mg/kg of supplemental Zn, freeze-dried ground beef produced the same tibia Zn concentration (and total Zn content) as that obtained with ZnSO4. The results suggest that the relative bioavailability of Zn in cooked ground beef is as great as that in ZnSO4, whether consumed in diets with or in those without phytate.

Based upon Zn uptake in chick tibia, Zn in raw and cooked pork loin was about 40% more bioavailable than that in ZnS04.H20. Neither roasting nor braising affected Zn bioavailability in the loin preparations. Adding 0.40% cysteine to diets containing ZnS04 improved Zn bioavailabilitv bv 73%. Pork loin is an excellent source of bioavailable Zn, and SH-containing compounds such as cysteine and glutathione that are present in meat may contribute to enhanced gut absorption of meat-source Zn.

No abstract