Dietary vitamin D3 requirement of Chinese yellow-feathered broilers

Three experiments have been conducted to investigate the effects of graded dietary levels of vitamin D3 ( VD3: ) on growth performance, metabolic regulation of calcium (CA), phosphorus (P), and bone development of Chinese yellow-feathered broilers during 3 growth phases: 1 to 21 d, 22 to 42 d, and 43 to 63 d. Dietary Ca and P in the corn-soybean-based diet were adequate. A total of 2,000 1-day-old, 1,600 22-day-old, and 1,600 43-day- old Lingnan yellow male broilers were randomly assigned to 1 of 8 dietary treatments with 5 replicates per treatment (50 birds per replicate for 1 to 21 d, 40 birds for both 22 to 42 d and 43 to 63 d). Dietary levels of VD3 were 100, 200, 300, 400, 500, 600, and 700 IU/kg for treatments 2 to 8 through the addition of VD3 to the basal mash diet which otherwise lacked detectable VD3. Graded doses of VD3 from 0 to 700 IU/kg in the diet produced linear (P<0.01) positive responses in ADG, ADFI, tibial weight, and breaking strength, and quadratic (P<0.01) responses in tibial length, bone density, ash, the levels of Ca and P in the ash , and the ratio of Ca to P. Serum concentrations of Ca, P, 25-hydroxycholecalciferol, osteocalcin, and calcitonin increased, and concentrations of fibroblast growth factor 23, Klotho protein, and parathyroid hormone all decreased with the increasing level of dietary VD3 (P<0.05). Adding VD3 improved meat color a* value and decreased shear force and drip loss of birds at 63 d (P<0.05). Considering bone characteristics and composition under the conditions of this study, it was concluded that the VD3 requirements of Chinese yellow-feathered broilers from 1 to 21 d for optimal tibial ash content were estimated from regression analysis to be 464 IU/kg from 1 to 21 d, 539 IU/kg from 22 to 42 d, and 500 IU/kg from 43 to 63 d.