SAFETY OF 25-HYDROXYCHOLECALCIFEROL AS A SOURCE OF CHOLECALCIFEROL INPOULTRY RATIONS

We conducted two safety studies of 25-hydroxycholecalciferol [25(OH)D- 3] in poultry broilers at levels ranging from 1 to 200 times those com monly used for cholecalciferol (vitamin D-3) supplementation in the in dustry. In the first experiment, 1-d-old male and female broiler chick ens were fed commercial diets containing either vitamin D-3 or 25(OH)D -3 at concentrations of 69, 207, and 690 mu g of 25(OH)D-3/kg of feed. The second experiment compared effects of 25(OH)D-3 and vitamin D-3 o n performance and survival of broilers at levels ranging from 1 to 200 times the basal level of 69 mu g/kg feed. When 25(OH)D-3 was fed in e qual amounts (wt/wt) to vitamin D-3, there was an increase in body wei ght and a decrease (improvement) in adjusted feed efficiency in both e xperiments, but the changes were significant only in the first experim ent. In the first experiment, serum 25(OH)D-3 concentrations increased from 13.3 +/- 4.3 to 42.5 +/- 18 ng/mL in birds fed vitamin D-3 or 25 (OH)D-3, respectively, and rose to 246 +/- 38 ng/mL in birds fed the h ighest level of 25(OH)D-3. Tissue 25(OH)D-3 concentrations were much l ower than serum concentrations and were highly correlated to the latte r, regardless of dietary treatment. In Experiment 2, there was some ev idence of renal calcification in birds fed 25(OH)D-3 at 10 times the b asal level, whereas dietary levels of vitamin D-3 of 50 times the basa l level were required to show some evidence of renal calcification. On the basis of both renal calcification and body weight, the present st udies would suggest that 25(OH)D-3 is 5 to 10 times more toxic than vi tamin D-3.