Relative bioavailability of organic zinc sources based on tissue zinc and metallothionein in chicks fed conventional dietary zinc concentrations

An experiment was conducted to estimate relative bioavailability (RBV) of Zn in Zinc proteinate and Zinc methionine compared to Zinc acetate as the standard. A total of 432, 1-day-old male broiler chicks was assigned randomly to dietary treatments which included the basal maize–soyabean meal diet (24 mg Zn kg−1 DM) supplemented with 0, 30, 60, or 90 mg kg−1 added Zn as reagent grade Zinc acetate or 30 or 60 mg kg−1 added Zn from Zinc methionine or Zinc proteinate fed for 3, 6, or 9 days. Accumulation of Zn in bone increased (P<0.001) with supplemental Zn and age. Bone Zn concentration was greater (P<0.001) in chicks given Zinc proteinate. Hepatic and mucosal metallothionein (MT) increased (P<0.001) with supplemented Zn and age. Using Zinc acetate as a standard (1.00) in multiple linear regressions gave estimated RBV values of 1.10, 1.24, and 1.16 for Zinc proteinate and 0.88, 0.91 and 0.78 for Zinc methionine at 3, 6, and 9 days, respectively, based on bone Zn concentrations. Similar estimates were calculated using mucosal MT. The coefficient of determination was greater for the mucosal MT regression at 3 days compared to that for bone Zn. Mucosal MT appears to be a suitable criterion to estimate bioavailability of Zn sources during short term trials.