ESTIMATION OF THE RELATIVE BIOAVAILABILITY OF INORGANIC COPPER SOURCES FOR SHEEP

Three experiments were conducted with sheep to assess the relative bio availability of copper (Cu) in supplemental Cu sources by measuring li ver uptake of Cu. In all experiments an initial liver biopsy was taken and then experimental diets were fed for 10 days. In Experiment 1, bo dy Cu stores were depleted by twice weekly intravenous injection for 3 weeks with ammonium tetrathiomolybdate before liver biopsies were tak en. Dietary treatments were the basal diet (8.7 mg/kg Cu) supplemented with 0, 20, 40, 60 or 80 mg/kg Cu as reagent grade cupric acetate (st andard) or 60 mg/kg Cu as feed grade cupric oxide, sulfate or carbonat e. In Experiment 2, the basal diet (8.3 mg/kg Cu) was supplemented wit h 0, 60, 120 or 180 mg/kg Cu from the standard, reagent grade cupric c hloride or 120 mg/kg Cu from feed grade cupric oxide, sulfate or carbo nate. In Experiment 3, the basal diet (12.6 mg/kg Cu) was supplemented with 0, 60, 120 or 180 mg/kg as reagent grade cupric chloride (standa rd) or 120 mg/kg Cu as reagent grade cupric acetate, or feed grade cup ric oxide or sulfate. At the end of the three experiments, lambs were killed and livers frozen for Cu analysis. Average relative bioavailabi lity values from Experiments 2 and 3 based on multiple linear regressi on of liver Cu concentration on added dietary Cu concentration with th e initial biopsy Cu as a covariate were 100, 93, 142, 121, and 35 from cupric chloride, acetate, sulfate, carbonate and oxide, respectively.