Estimated relative bioavailability of supplemental inorganic molybdenum sources and their effect on tissue molybdenum and copper concentrations in lambs

Forty crossbred wether lambs, 44 kg initial body weight, were used to study relative bioavailability of Mo in supplemental Mo sources and their effects on body Cu storage. The basal maize-soya-bean meal-cottonseed hulls diet contained 11.5 mg kg−1 Cu, 1.1 mg kg−1 Mo and 2.1 g kg−1 S (DM basis) and was supplemented with 0, 15, 30, or 45 mg kg−1 (as-fed basis) added Mo as reagent grade sodium molybdate as the standard, or 30 mg kg−1 added Mo as ammonium molybdate, molybdenum trioxide, or molybdenum metal. Diets were fed for 28 days and feces and urine were collected for the last 5 days and composited by lamb. At the end of the trial, serum, liver, kidney, muscle, and bile were collected and analyzed for Mo and Cu. Based on multiple regression slope ratios of tissue concentration or daily excretion (including that from bile) of Mo on added dietary Mo concentration, the average relative bioavailability values were 1.00, 1.04, 1.10 and 0.18 for sodium molybdate, ammonium molybdate, molybdenum trioxide, and molybdenum metal. Serum and muscle Mo concentrations had the best fits to a linear model. Kidney Cu, serum total Cu, serum TCA-insoluble Cu, and fecal Cu concentrations increased with increasing dietary intakes of Mo.