This experiment was conducted to examine the effect of three levels of crude protein (CP) (NRC, 15% more than NRC and 15% less than NRC) and three levels of Ca and available P (Av. P) (NRC, 15% more than NRC and 15% less than NRC) on performance of broilers from hatching until 21 days of age. The experimental design was a completely randomized design (CRD), with a 3 × 3 factorial arrangement of nine dietary treatments. Each treatment combination had four replicate pens (10 birds per pen). Results of this experiment showed that CP content had no significant effect on feed and water intake. However, body weight gain (BWG) significantly reduced and FCR increased (P < 0.05) by 15% change in CP content of diet. Fifteen percent increase in mineral content of diets had no significant effect on feed intake. However, increase in Ca and Av. P significantly increased BWG and resulted in an improved feed conversion ratio (FCR) and increased water intake. There was an interactive effect of CP by Ca and Av. P levels on feed intake, BWG and FCR. A change in CP or mineral content of the diets had no significant effect on blood parameters except for potassium concentration (K+). Reducing CP, Ca and Av. P content of the diet significantly (P < 0.001) increased P, Ca and N retention. Reduction in CP content of the diet led to a decrease in length, P and tibia bone ash. There was an interactive effect of CP by Ca and Av. P on the retention of Ca, N and ash of tibia bone.

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