Effects of Broiler Strain, Dietary Nonphytate Phosphorus, and Phytase Supplementation on Chick Performance and Tibia Ash

Three experiments were conducted to study the effects of broiler strain and phytase supplementation on chick nonphytate P (NPP) requirements for growth, feed intake, and tibia ash. The first experiment compared the NPP requirements for 8- to 22-d-old chicks from 2 broiler strains, Ross 308 and 708, that have been selected for differences in early weight gain and performance. The second experiment utilized similar 8- to 22-d-old Ross 308 and 708 chicks but also compared the effects of dietary fungal phytase supplementation (600 U/kg) on broiler NPP requirements. The third experiment utilized a younger starting age, 5 to 23 d old, for Ross 308 and 708 chicks with and without phytase supplementation. Minor differences in chick growth did not affect chick NPP requirements in Experiments 1 and 3, but a substantial and unexplained reduction of growth of the Ross 708 chicks in Experiment 2 resulted in a lower NPP requirement for chick growth and feed intake but not for tibia ash. As expected, supplementation of diets with fungal phytase did result in decreased NPP requirements for growth, feed intake, and tibia ash in both strains used in Experiment 3.