Estimation of the standardized ileal digestible calcium and phosphorus requirements of broiler chickens from 10 to 21 days of age

The current study aimed to estimate the standardized ileal digestible (SID) calcium (Ca) and phosphorus (P) requirements of broiler chickens based on response surface methodology (RSM). Nine experimental diets were formulated with different SID Ca and P concentrations (2.80 and 5.50, 3.44 and 4.44, 3.44 and 6.56, 5.00 and 7.00, 5.00 and 5.50, 5.00 and 4.00, 6.56 and 4.44, 6.56 and 6.56, and 7.20 and 5.50 g/kg, respectively). A total of 480 10-day-old Ross 308 male broilers were weighed and randomly assigned to nine treatments based on body weight. Each treatment had five replicates, except for the central treatment (5.00 g/kg Ca and 5.50 g/kg P), which had eight replicates with 10 birds per pen. On day 21, body weight and feed leftovers were recorded to calculate body weight gain (BWG) and the gain-to-feed ratio (G:F). Left tibia bones were also collected for compositional analysis and bone mineral density (BMD) assessment. Response surface analysis revealed significant quadratic models for all criteria. The maximum BWG was estimated at 5.13 and 5.74 g/kg for SID Ca and P, respectively. The maximum G:F was observed when 6.41 and 7.00 g/kg of SID Ca and P were used, respectively. Multi-objective optimization analysis demonstrated that 6.02 g/kg of SID Ca and 6.61 g/kg of SID P were required to achieve both optimal BWG and G:F. Furthermore, the ideal SID Ca and P concentrations for optimal tibia ash, tibia Ca, tibia P, and BMD were estimated at 7.20 and 7.00 g/kg, 5.75 and 5.87 g/kg, 7.20 and 7.00 g/kg, and 7.20 and 6.96 g/kg, respectively. Multi-objective optimization indicated that 6.50 and 6.83 g/kg of SID Ca and P, respectively, are required to achieve optimal growth performance and bone mineralization. This study's findings suggest that RSM is a feasible and effective approach to determining the optimal SID Ca and P requirements of broiler chickens, as it efficiently evaluates multiple factors while considering several response criteria.