This study evaluated the effect of dietary calcium (Ca) and available phosphorus (aP) restriction on growth performance, nutrients retention (ATTR), serum metabolites, and tibia in broiler chickens. A total of 720 one-d-old Ross-308 broilers were used in this study. Broilers were fed with 0 (control), 10 (L1), 20 (L2), and 30% (L3) aP-deficient starting (ST) diets during 1-10 d. In ST period, control included 6 and others included 18 replicates of 12 chicks. In post-starter (PST) period, control was still fed with standard diets, while restricted groups were divided into 3 groups and fed with L1, L2, and L3 diets. Each PST treatment included 6 replicates of 12 chicks. Data were analysed using a completely randomized design in a 1 (control)+3×3 factorial arrangement. Factors included aP levels in ST and PST diets. Results showed that L3 diet decreased feed intake and weight gain but increased ATTR of Ca in starter phase in compare with control group (p < .05). Retarded growth of birds was compensated in post-starter phase. The Ca, P and ALP levels in blood serum were not significantly influenced by aP levels on d 10 and d 42. The ATTR of Ca and tP on d 42, were higher in birds fed L3 diets than L2 or L1 groups (p < .05). The main effect of L3 group in both ST and PST, decreased (p < .05) tibia ash, Ca, and P in compare with L1 group. Main effect of post-starter L3 group had lowest femur breaking strength (p = .007). In general, restriction in dietary aP increased nutrients ATTR, impaired bone mineralization and strength without affecting growth performance.

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