Effects of high dietary molybdenum concentration and duration of feeding time on molybdenum and copper metabolism in sheep

An experiment was conducted to determine the effect of elevated dietary Mo and duration of feeding on tissue concentrations and excretion of Mo and Cu. Forty lambs were fed diets containing 0, 15, 30 or 45 mg kg−1 (as-fed basis) added Mo as sodium molybdate for 14 or 28 days. The basal corn-soya-bean meal-cottonseed hulls diet contained 1.2 mg kg−1 Mo, 11 mg kg−1 Cu, and 2.2 g kg−1 S (DM basis). Concentration of Mo increased linearly in feces, urine, serum, liver, kidney and muscle as dietary Mo increased. There was no effect of time on fecal, urinary, liver or muscle Mo concentrations. Liver Mo concentration increased (p < 0.0001) more rapidly in response to dietary Mo at 14 days than at 28 days, but kidney and muscle Mo increased (p < 0.05) to a greater extent in lambs fed 28 days than in those fed 14 days. Muscle Cu decreased (p < 0.01) with increasing dietary Mo regardless of feeding duration and kidney Cu tended (p = 0.05) to increase at 28 but not 14 days. Total serum Cu and TCA-insoluble serum Cu also increased (p < 0.001) at 28 days with increasing dietary Mo. Dietary supplementation of Mo as sodium molybdate resulted in a redistribution of body stores of Cu in lambs fed normal concentrations of dietary Cu with constant S. It appears that urinary excretion and tissue concentrations of Mo may be useful to estimate bioavailability of supplemental sources of the element.