Bioavailability of copper in analytical-grade and feed-grade inorganic copper sources when fed to provide copper at levels below the chick's requirement.

Young chicks were fed a casein-soy protein concentrate basal diet (.56 mg Cu/kg) containing graded levels of added Cu (0, .5, 1.0 mg/kg) from analytical-grade (AG) CuSO4.5H2O, Cu2O, CuO, CuCO3.Cu(OH)2, CuCl, and also from feed-grade (FG) CuSO4.5H2O and FG-CuO. Weight gain, hematocrit, hemoglobin, plasma Cu, liver Cu, gall bladder (bile) Cu, and tendon lysine were assessed to determine whether dose-dependent Cu responses would occur. Gall bladder Cu concentration as well as total Cu content of the gall bladder were found to be linear functions of supplemental Cu intake. Common-intercept multiple linear regression (slope-ratio) of bile Cu concentration regressed on supplemental Cu intake indicated Cu bioavailability values (relative to the standard, AG-CuSO4.5H2O, set at 100%) of 97.9% for AG-Cu2O, 93.5% for FG-CuSO4.5H2O, and 112.9% for AG-CuCO3.Cu(OH)2. These values were not different (P > .05) from 100%. Relative bioavailability of Cu in AG-CuCl was 142.5%, which was different (P < .05) from the standard. Both AG-CuO and FG-CuO gave Cu bioavailability estimates not different (P > .05) from zero. The results indicate that when Cu levels are fed below the chick's requirement, bile Cu concentration is a sensitive indicator of net gut absorption of Cu.