Evaluation of Relative Bioavailability of 25-Hydroxycholecalciferol to Cholecalciferol for Broiler Chickens

This study was conducted to evaluate the relative bioavailability (RBV) of 25-hydroxycholecalciferol (25-OH-D-3) to cholecalciferol (vitamin D-3) in 1- to 21-d-old broiler chickens fed with calcium (Ca)- and phosphorus (P)-deficient diets. On the day of hatch, 450 female Ross 308 broiler chickens were assigned to nine treatments, with five replicates of ten birds each. The basal diet contained 0.50% Ca and 0.25% non-phytate phosphorus (NPP) and was not supplemented with vitamin D. Vitamin D-3 was fed at 0, 2.5, 5.0, 10.0, and 20.0 mu g/kg, and 25-OH-D-3 was fed at 1.25, 2.5, 5.0, and 10.0 mu g/kg. The RBV of 25-OH-D-3 was determined using vitamin D-3 as the standard source by the slope ratio method. Vitamin D-3 and 25-OH-D-3 intake was used as the independent variable for regression analysis. The linear relationships between the level of vitamin D-3 or 25-OH-D-3 and body weight gain (BWG) and the weight, length, ash weight, and the percentage of ash, Ca, and P in femur, tibia, and metatarsus of broiler chickens were observed. Using BWG as the criterion, the RBV value of 25-OH-D-3 to vitamin D-3 was 1.85. Using the mineralization of the femur, tibia, and metatarsus as criteria, the RBV of 25-OH-D-3 to vitamin D-3 ranged from 1.82 to 2.45, 1.86 to 2.52, and 1.65 to 2.05, respectively. These data indicate that 25-OH-D-3 is approximately 2.03 times as active as vitamin D-3 in promoting growth performance and bone mineralization in broiler chicken diets.