Evaluation of cholecalciferol sources using broiler chick bioassays

Three experiments were conducted to test the potencies of nine sources of c holecalciferol using a chick bioassay. The tested products were compared wi th a Sigma Reference Standard (SRS). All of the diets fed to the chicks wer e prepared from corn-soybean meal. Each of the products was in premix form containing cholecalciferol. Their physical characteristics reflected the me thods used to produce the premixes. They were categorized as spray-dried or drum-dried in the beadlet or flake form. Basal diets without cholecalcifer ol were used in all experiments. For Experiments 1 and 2, the designs were a 2 x 3 factorial arrangement using three different cholecalciferol product s and two levels of 200 and 400 IU/kg dietary cholecalciferol. For both exp eriments, three additional SRS levels of 600, 800, and 1,000 IU/kg were inc luded in the studies as positive controls as there is a possibility that th e cholecalciferol products being tested may exhibit activity higher than th e amount stated. In Experiment 3, a 3 x 4 factorial arrangement was used, w hich was represented by three cholecalciferol products and four levels of d ietary cholecalciferol at 150, 300, 600, and 1,200 IU/kg. By using the slop e ratio analysis, the potencies of the products from the three experiments were between 86 and 118%. In Experiment 3, the requirement of chicks for ch olecalciferol using the three tested products, as determined by a nonlinear regression model based on bone ash, were 843 +/- 85, 911 +/- 106, and 986 +/- 131 IU/kg of diet as compared with 915 +/- 82 IU/kg when using the SRS. The results from these studies indicate that the chemical assays used to d etermine the cholecalciferol activity of these products were very reliable.