Abstract
1α-Hydroxycholecalciferol (1α-OH-D(3)) is an active vitamin D derivative. In this study, three experiments were conducted to evaluate the optimal dietary levels of 1α-OH-D(3) in broiler chickens from 1 to 42 days of age. 1α-OH-D(3) levels used were 0, 1.25, 2.5, 5, and 10 µg/kg in experiment 1, 0.625, 1.25, 2.5, 5, 7.5, and 10 µg/kg in experiment 2, and 2, 2.5, 3, 3.5, 4, 4.5, and 5 µg/kg in experiment 3. In experiment 1, the addition of 0 to 10 µg/kg of 1α-OH-D(3) quadratically improved growth performance, tibia development, and mRNA expression levels of nuclear vitamin D receptor (nVDR), membrane vitamin D receptor (mVDR), and type IIb sodium-phosphate cotransporter (NaPi-IIb) in the duodenum of broiler chickens from 1 to 12 days of age. Body weight gain (BWG), the weight and ash weight of the tibia, and mRNA expression levels of mVDR and NaPi-IIb of broilers fed with 0 and 10 µg/kg of 1α-OH-D(3) were lower than those of birds fed with 2.5 µg/kg of 1α-OH-D(3). In experiment 2, 1α-OH-D(3) levels were quadratically related to BWG and to weight and ash weight of the femur and the tibia of broiler chickens at 42 days of age. The highest values of growth performance and bone mineralization were recorded in broilers fed with 2.5 to 5 µg/kg of 1α-OH-D(3). In experiment 3, there was no difference observed in BWG and the weight and ash weight of the femur and the tibia of the 42-day-old broilers fed with 2 to 5 µg/kg of 1α-OH-D(3). These data suggest that the optimal dietary levels of 1α-OH-D(3) were 2 to 5 µg/kg for broiler chickens from 1 to 42 days of age.