BIOAVAILABILITY OF ZINC FROM INORGANIC AND ORGANIC SOURCES FOR PIGS FED CORN-SOYBEAN MEAL DIETS

Two experiments were conducted with pigs 1) to determine the effect of supplemental Zn on growth performance, bone Zn, and plasma Zn in pigs fed Zn-unsupplemented, corn-soybean meal diets and 2) to assess bioav ailability of Zn from inorganic and organic Zn sources. In both experi ments, weanling pigs were fed a diet with no supplemental Zn for 5 wk to deplete their Zn stores. In Exp. 1, 192 pigs were fed a corn-soybea n meal diet (growing diet, 32 mg/kg of Zn; finishing diet, 27 mg/kg of Zn) supplemented with feed-grade ZnSO4.H2O to provide 0, 5, 10, 20, 4 0, and 80 mg/kg of supplemental Zn. Supplemental Zn did not affect wei ght gain, feed intake, or gain/feed during either the growing or the f inishing period (P > .05). However, bone and plasma Zn concentrations increased linearly(P < .01) in response to supplemental Zn at dietary Zn levels between 27 mg/kg (basal) and 47 mg/kg (breakpoint). In Exp. 2, three levels of supplemental Zn from ZnSO4.H2O (0, 7.5, and 15 mg/k g kg of supplemental Zn) were used to construct a standard curve (meta carpal, coccygeal vertebrae, and plasma Zn concentrations regressed on supplemental Zn intake; R(2) = .93, .89, and .82, respectively). From the standard curve, the bone and plasma Zn concentrations obtained fr om pigs fed 15 mg/kg of supplemental Zn from ZnO and 7.5 mg/kg of supp lemental Zn from Zn-methionine (ZnMET) and Zn-lysine (ZnLYS) were used to calculate bioavailable Zn via multiple linear regression, slope-ra tio analysis. The estimates of Zn bioavailability differed depending o n which variable was used. Overall trends indicated the following rank ings: ZnSO4.H2O > ZnMet > ZnO > ZnLys.