Evaluation of cholecalciferol sources using broiler chick bioassays.

Three experiments were conducted to test the potencies of nine sources of cholecalciferol using a chick bioassay. The tested products were compared with a Sigma Reference Standard (SRS). All of the diets fed to the chicks were prepared from corn-soybean meal. Each of the products was in premix form containing cholecalciferol. Their physical characteristics reflected the methods used to produce the premixes. They were categorized as spray-dried or drum-dried in the beadlet or flake form. Basal diets without cholecalciferol were used in all experiments. For Experiments 1 and 2, the designs were a 2 x 3 factorial arrangement using three different cholecalciferol products and two levels of 200 and 400 IU/kg dietary cholecalciferol. For both experiments, three additional SRS levels of 600, 800, and 1,000 IU/kg were included in the studies as positive controls as there is a possibility that the cholecalciferol products being tested may exhibit activity higher than the amount stated. In Experiment 3, a 3 x 4 factorial arrangement was used, which was represented by three cholecalciferol products and four levels of dietary cholecalciferol at 150, 300, 600, and 1,200 IU/kg. By using the slope ratio analysis, the potencies of the products from the three experiments were between 86 and 118%. In Experiment 3, the requirement of chicks for cholecalciferol 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 determine the cholecalciferol activity of these products were very reliable.