| Summary: | Summary: An experiment was conducted to evaluate the effects of dietary nonphytate phosphorus level and a novel corn-expressed phytase (GraINzyme, Agrivida Inc., Woburn, MA) supplementation on broiler growth performance and bone mineralization. Broilers were fed graded levels of nonphytate phosphorus from 0.20 to 0.44% increased by 0.06% and 4 levels of corn-expressed phytase (500; 1,500; 3,000; and 4,500 FTU/kg). Dicalcium phosphate was used as the reference for inorganic phosphorous. Increasing dietary nonphytate phosphorus level or supplementation of phytase linearly (P < 0.01) increased the bodyweight gain, feed intake, tibia fat–free dry weight, ash weight, ash percentage, and ash concentration. Feed conversion ratio was linearly (P < 0.01) improved as the dietary nonphytate phosphorus level was gradually increased. Graded nonphytate phosphorus levels were log-transformed and regressed against the bodyweight gain, tibia ash weight, ash percentage, and ash concentration for calculating the nonphytate phosphorus relative to the phytase efficacy. Both raw and standardized responses were regressed against dietary nonphytate phosphorus levels. Bodyweight gain was less sensitive than bone mineralization results. From the regression estimates using standardized responses, bodyweight gain was about 92% of tibia ash concentration in terms of sensitivity. The calculated nonphytate phosphorus relative to the equivalence for bodyweight gain, tibia ash weight, ash percentage, and ash concentration were 0.166, 0.158, 0.163, and 0.183%, respectively. Results suggest that the corn-expressed phytase is effectively released in the P form phytate and improves broiler growth performance and bone mineralization. Bone mineralization is a better indicator for the broiler response to dietary nonphytate phosphorus levels than bodyweight gain.
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