Abstract:

【Objective】 An experiment was conducted to investigate the requirement of nonphytate phosphorus (NPP) and efficacy of a genetically engineered yeast phytase (PHY A) by Lingnan yellow broilers from 22 d to 42 d. 【Method】 A total of 1320 one-day-old male chicks were randomly divided into eleven dietary treatment groups, which consisted of four replicate floor pens with 30 birds per pen. The control group (Treatment 1) was fed with basal diet of NPP 0.08% without dicalcium phosphate or phytase supplementation. Dietary levels of NPP were 0.16, 0.24, 0.32, 0.40, 0.48, and 0.56%, respectively, for treatments 2 to 7, through addition of dicalcium phosphate (chemistry grade) to the basal diet. Diets of treatments 8 to 11 were supplemented with PHY A at 200, 400 and 600 U•kg-1, a commercial phytase product (PHY B) at 400 U•kg-1 level, respectively. 【Result】 The birds in 0.32%-0.56% NPP groups gained more than those of the other groups (P＜0.05). The NPP supplementation significantly improved feed intake (P＜0.05). The feed gain ratio was significantly decreased by 0.40% NPP diet compared to the control birds (P＜0.05). The level of 0.48% NPP was required for optimum tibia development. The additions of PHY A at 400 U•kg-1 and 600 U•kg-1 level and PHY B all significantly improved ADG (P＜0.05), ADFI (P＜0.05), and dry defatted tibia weight (P＜0.05). And the percentage of tibia ash was increased by 600 U•kg-1 PHY A supplementation (P＜0.05).【Conclusion】The requirements of NPP for maximal ADG and highest percentage tibia ash both are 0.40%. The phosphorus equivalency value of PHY A is estimated at 685 U•kg-1 for male yellow broilers of 22-42 day old.

Key words: nonphytate phosphorus, growth, tibia ash, genetically engineered yeast phytase, phosphorus equivalency value, yellow broilers