BIOLOGICAL EFFICACY OF COPPER IN CHICKEN BILE

Newly hatched chicks were fed a Cu-deficient casein-soybean concentrate diet (0.56 mg Cu/kg) during an 8-d pretest period, after which they were fed experimental diets containing graded levels of added Cu from CuSO4.5H2O during a 15-d assay period. Following the Cu-depletion period, gall bladder Cu concentration decreased from 645 nmol/g dry matter at hatching to 60 nmol/g dry matter at d 8 posthatching; liver Cu concentration decreased during the same period from 255 to 225 nmol/g dry matter. During the subsequent 15-d repletion period, a sevenfold linear increase in gall bladder Cu occurred as Cu was supplemented up to 2 mg Cu/kg, after which it declined gradually in birds fed graded doses between 2 and 16 mg Cu/kg. Liver Cu also increased linearly as Cu was supplemented up to 2 mg/kg; when chicks were fed between 2 and 16 mg/kg of supplemental Cu, liver Cu concentration remained constant. Bile obtained from chicks fed 800 mg Cu/kg diet for 22 d was freeze-dried, analyzed and found to contain 3.05 mumol Cu/g dry matter. When 8-d-old Cu-depleted chicks were fed graded levels of supplemental Cu (0, 0.5 and 1.0 mg Cu/kg) from CuSO4.5H2O, bile Cu concentration increased linearly from 10.5 to 102.7 mumol/L. Bile Cu did not increase when freeze-dried bile (1.0 mg Cu/kg diet) was supplemented. When 0.5 mg Cu/kg from CuSO4.5H2O was supplemented in combination with 0.5 mg Cu/kg from freeze-dried bile, bile Cu concentration was less than one-half the level present in chicks fed 0.5 mg Cu/kg from CuSO4.5H2O alone. The results suggest that biliary Cu entering the gut is in a form that cannot be reabsorbed by chickens.