Abstract
The effects of varying dietary Ca, available phosphorus (AP), and protein on 5- to 17-day performance (growth and feed efficiency), Ca and P contents of tibia and plasma, ME, and N utilization of broiler chickens were investigated in three experiments. In Experiment 1, high dietary Ca (24.3 versus 11.8 g/kg) reduced performance, N digestibility, and ME, whereas N retention was not affected. Reducing dietary protein (186 or 203 versus 217 g/kg) reduced performance and N retention but increased ME. In Experiment 2, high dietary Ca (25.3 versus 10.7 g/kg) reduced performance, tibia Ca, and plasma P and increased plasma total Ca; whereas the diet with both high Ca (25.3 g/kg) and high AP (9.8 versus 4.3 g/kg) reduced only performance. Reducing dietary protein from 206 to 166 g/kg diet reduced growth but improved feed efficiency and tibia P content. In Experiment 3, a diet containing 25.6 g of Ca and 4.9 or 10.7 g of AP compared with a diet containing 11.2 g of Ca and 4.9 g of AP/kg of diet reduced performance. Reducing dietary protein from 236 to 215 g/kg of diet decreased performance. It was concluded that high dietary Ca reduced growth performance and feed efficiency and that altering the dietary protein from 166 to 236 g/kg of diet did not overcome the growth depression effect of high Ca or of high Ca and AP diets.