Effect of sequential feeding of phosphorus-deficient diets and high-dose phytase on efficient phosphorus utilization in broiler chickens

An experiment was conducted to investigate the effectiveness of sequential feeding of a very low non-phytate P (NPP) diet supplemented with varying doses of phytase to broiler chickens. A total of 450 one-day-old male broiler chickens were fed a standard diet up to 14 d of age, then allotted to 6 dietary treatments (with 5 replicates of 15 broiler chickens each) from d 14 to 42. Dietary treatments included a positive control [PC; 4.35 g NPP/kg (d 14 to 28) and 3.95 g NPP/kg (d 28 to 42)], a negative control without any inorganic P source [NC; 1.50 g NPP/kg (d 14 to 28) and 1.36 g NPP/kg (d 28 to 42)], and a negative-positive control (NPC), in which broiler chickens received the PC for 24 h and then fed the NC (including 0, 500, 1,500, or 3,000 FTU phytase/kg) for the following day in a 48-h-cycle sequential feeding program. The Ca to NPP ratio was maintained at 2 to 1 in all formulations. The NC diet decreased overall feed intake (FI) and serum P compared to those of the PC diet (P = 0.047 for overall FI; P < 0.001 for serum P). Broiler chickens fed the NC diet had lower overall body weight gain (BWG), carcass yield, tibia ash, and tibia P than those fed the PC diet (P < 0.001), and the NPC diet failed to fully restore such losses. The inclusion of 500 FTU phytase/kg in the NPC diet recovered BWG, carcass yield, tibia ash, tibia P, and tibia strength losses by feeding the low-P diet to the PC values. Overall feed conversion ratio (P = 0.031), total P retention (P < 0.001), tibia ash (P < 0.001), and tibia P (P = 0.001) were improved linearly with increasing doses of phytase in the NPC diet. It was concluded that sequential feeding of the very low-NPP diet failed to recover all growth losses noted on the NC, but the inclusion of 500 FTU phytase/kg in the NPC diet restored the growth and bone mineralization losses to the PC values. Also, sequential feeding of the very low-NPP diets with increasing phytase doses had increasingly beneficial effects on overall growth performance.