RESPONSE TO HIGH DIETARY COPPER AND DURATION OF FEEDING TIME ON TISSUE COPPER CONCENTRATION OF SHEEP

Two experiments were conducted to study the effect of high dietary Cu and duration of feeding time on tissue mineral composition of sheep to establish a standard curve for future bioassay of supplemental Cu sou rces. In Experiment 1, 24 crossbred wethers were fed a basal diet (9.2 4 mg/kg Cu) supplemented with 15, 30 or 45 mg/kg added Cu as cupric ac etate for 15 or 30 days. An additional four sheep were killed at day 0 to serve as controls. In Experiment 2, 30 crossbred wethers were inje cted i.v. with 50 mg ammonium tetrathiomolybdate (ATM) twice weekly fo r 3 weeks to reduce body Cu stores, then fed the basal diet (7.29 mg/k g Cu) or the basal plus 20, 40, 60 or 80 mg/kg added Cu as cupric acet ate for 10 or 20 days. Treatment with ATM reduced liver Cu stores by 5 2%. In Experiment 1, liver and bone Cu concentrations were greater in sheep supplemented with Cu compared with controls, but there was no di fference among sheep fed various added Cu concentrations. In Experimen t 2, liver Cu concentration increased linearly in sheep fed 10 days an d quadratically in sheep fed 20 days, but serum, spleen and kidney Cu concentrations were not affected by treatment. A bioassay for Cu bioav ailability based on liver Cu uptake with a 10-day supplementation peri od appeared feasable.