Nutritional Evaluation of a Copper-Methionine Complex for Chicks

Three chick experiments were conducted to evaluate a new Cu complex product, Cu-Met. Relative bioavailability of Cu was assessed with two bioassay systems, one employing bile Cu concentration as the criterion at Cu-deficient levels and another employing liver Cu concentration at Cu-excess levels. Relative bioavailability of Met was assessed separately. Common-intercept multiple linear regression (slope-ratio) of bile Cu concentration or liver Cu concentration regressed on supplemental Cu intake was used to assess Cu bioavailability relative to the standard, analytical-grade CuSO4.5H2O, which was set at 100%. In addition, Cu-Lys and CuCl (compounds previously evaluated by bile Cu concentration) were evaluated by the liver Cu accumulation method. Relative bioavailability of Cu in Cu-Met was estimated as 96% by the bile Cu assay and 88% by the liver Cu assay, which were not different (P > .05) from 100%. The liver Cu assay estimated that relative Cu bioavailabilities in Cu-Lys and CuCl of 114 and 145% (P < .05), respectively. These values were very close to those previously estimated by the bile Cu assay. Relative Met bioavailability of Cu-Met was 100% of the standard, i.e., feed-grade DL-Met.