Influence of dietary calcium concentrations and the calcium-to-non-phytate phosphorus ratio on growth performance, bone characteristics, and digestibility in broilers

Two experiments were conducted to determine the influence of dietary Ca concentrations (Experiment 1) and a combination of dietary Ca and non-phytate phosphorus (NPP) to create distinct Cato- NPP ratios (Experiment 2) in corn-soybean meal diets fed to broiler chickens from 2 to 23 d of age. In Experiment 1, dietary treatments consisted of 7 concentrations of Ca (0.4, 0.6, 0.8, 1.0, 1.2, 1.4, or 1.6% of the diet; 7 treatments total), and NPP concentrations were maintained at 0.3%. Increasing the dietary Ca concentration while maintaining 0.3% NPP elicited linear reductions (P < 0.01) in overall growth performance and tibia ash. Dietary effects also were observed for apparent retention of P and Ca, which decreased (P < 0.05) linearly or quadratically for birds receiving dietary treatments with Ca concentrations greater than 0.6%. In Experiment 2, diets were formulated to contain 3 concentrations of Ca (0.4, 1.0, or 1.6% of the diet) with NPP concentrations either constant at 0.45% or adjusted to maintain a dietary Ca-to-NPP ratio of 2:1 (6 treatments total). Growth performance was not influenced by Ca concentration or the Ca-to-NPP ratio. Tibia break force was lower (P < 0.01) in birds fed diets containing 0.4% Ca, regardless of the NPP concentration. Tibia ash increased (P < 0.01) as the dietary Ca concentration increased. Neither the dietary Ca nor NPP concentrations affected nitrogen retention (P > 0.05). Upon maintaining a constant 2:1 Ca-to- NPP ratio, P and Ca retention decreased (P < 0.01) at the highest Ca concentration. In conclusion, imbalanced Ca and NPP adversely influenced growth performance and nutrient retention of broilers, indicating the concentrations of Ca and NPP required to maximize bone structure and function may be higher than those required for performance.