The present study was aimed to investigate the effects of nano-vitamin D3 (NVD3) and micro-vitamin D3 (MVD3) on performance and bone parameters in broiler chickens. A total of 792 one-d-old Cobb 500 male broiler chickens were randomly distributed in a completely randomized design according to a 2×6 factorial arrangement of 12 dietary treatments with six replicates of 11 chicks. The treatments were: basal diet (control); basal diet supplemented with 100, 200, 400, 800, and 1600 (IU/kg diet) commercial MVD3; and a basal diet supplemented with the same levels of NVD3. The basal diet consisted of 0.5% Ca and 0.25% non-phytate phosphorus and was free of vitamin D3. There were significant differences (P<0.01) in feed conversion ratio due to supplementation with NVD3 from 4 to 10, 11 to 21, and 4 to 21 days of age compared to those receiving MVD3. The chicks receiving NVD3 had significantly (P<0.01) higher live body weight (LBW) at 21-d of age and daily weight gain from 4 to 21-d of age compared to MVD3. The chicks receiving NVD3 had a significantly (P<0.01) higher concentration of ash and Ca content in the tibia. Bone stiffness and strength, tibia weight per length index, tibia weight, tibia diameter, organic matter (OM), OM/ash, and OM/length at 21-d were significantly (P<0.01) improved in birds fed diets supplemented with NVD3. Relative bioavailability of the NVD3 source to the MVD3 was more efficient according to performance and bone mineralization measurements. There was better growth performance and bone parameters in the 800 and 1,600 IU/kg levels than at the other levels. Assessing the data of all experimental indexes showed that 800 IU/kg exhibited significant linear effects, suggesting that it can be the ideal level of supplementation of NVD3, and, on the other side, the rate of 1600 IU/kg could be the maximum supplementation of NVD3 in broiler chickens.

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