BIOAVAILABILITY OF COBALT SOURCES FOR RUMINANTS .2. ESTIMATION OF THERELATIVE VALUE OF REAGENT GRADE AND FEED GRADE COBALT SOURCES FROM TISSUE COBALT ACCUMULATION AND VITAMIN-B-12 CONCENTRATIONS

Three experiments were conducted to estimate the bioavailability of co balt (Go) in reagent grade and feed grade Co sources for sheep. In Exp eriments 1 and 2, 27 mature sheep were assigned randomly to nine treat ment groups. Treatments were the basal diet supplemented with 0, 20, 4 0, or 60 ppm reagent grade (RG) Co sulfate (standard) or 40 ppm Co as either RG Co oxide or Co carbonate or feed grade (FG) Co oxide, Co car bonate, or a Co oxide by-product (BP). Sheep were fed the experimental diets for 20 days. In Experiment 1, liver, kidney, heart, muscle, and spleen were collected. In Experiment 2, liver, kidney, and serum were collected. In Experiment 3, lambs were fed the basal control diet or basal supplemented with 0, 20, 40, or 60 ppm Co as RG Co sulfate or FG Co glucoheptonate for 16 days and liver, kidney, and serum were colle cted. Vitamin B-12 was determined in serum and liver in Experiment 3. Cobalt concentration was determined on all other samples. There was no effect of Co treatment on feed intake in any of the experiments. Tiss ue Co concentrations increased with Co supplementation in all three tr ials. In Experiment 1, serum and liver vitamin B-12 concentrations inc reased with increasing Co up to 40 ppm added Co. In Experiment 3, vita min B-12 concentrations were variable but generally decreased with inc reasing Co as did total corrinoid concentrations. Based on liver and k idney Co concentrations the Co in Co sulfate, both carbonates and the glucoheptonate was more available than that in any of the three oxide forms. (C) 1997 Elsevier Science Inc.