An experiment was conducted to investigate the effect of dietary calcium ( Ca ) or phosphorus ( P ) deficiency on bone development and related Ca or P metabolic utilization parameters of broilers. A total of 504 one-day-old Arbor Acres male broilers were randomly assigned to 1 of 4 treatments with 7 replicates of 18 birds per replicate in a completely randomized design. A 2 (Ca levels: 1.00 and 0.35%) × 2 (nonphytate P [ NPP ] levels: 0.45 and 0.23%) factorial arrangement of treatments was adopted in the 21-day trial. The 4 treatments were the Ca- and P-adequate diet (1.00% Ca + 0.45% NPP), the Ca-deficient diet (0.35% Ca + 0.45% NPP), the P-deficient diet (1.00% Ca + 0.23% NPP), and the Ca- and P-deficient diet (0.35% Ca + 0.23% NPP). The greatest impact on tibia bone mineral density, bone breaking strength, and ash content was in the P-deficient diets, especially in broilers fed with the Ca-adequate diet, whereas adequate P and reduced Ca reduced ( P < 0.05) these parameters compared with adequate Ca and P, but not to the same level as P deficiency. Furthermore, dietary Ca or P deficiency, especially adequate Ca and P deficiency decreased ( P < 0.05) serum P, 25-hydroxyvitamin D 3 ( 25-OHD 3 ) contents, and tibia ash Ca and P contents but increased ( P < 0.05) the serum Ca content and tibia alkaline phosphatase ( ALP ) activity compared with adequate Ca and P. The results from this study indicated that the bone development and Ca or P metabolic utilization parameters of broilers were the most sensitive ones to dietary P deficiency, followed by dietary Ca deficiency or Ca and P deficiencies. Dietary P deficiency impaired the bone development by increasing serum Ca content and tibia ALP activity but decreasing serum P, 25-OHD 3 contents, and tibia ash Ca and P contents of broilers. Dietary Ca deficiency impaired bone development by increasing serum Ca content, tibia ALP activity, and tibia ash P content but decreasing serum P, 25-OHD 3 contents, and tibia ash Ca content of broilers.

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