Nonphytate Phosphorus Requirement and Efficacy of a Genetically Engineered Yeast Phytase for Yellow Broilers at 22- to 42-d-Old Age

An experiment was conducted to investigate the requirement of nonphytate phosphorus (nPP) and efficacy of a genetically engineered yeast phytase (PHY A) for Lingnan yellow broilers from 22- to 42-d-old age. A total of 1 320 1-d-old male chicks were randomly divided into 11 dietary treatment groups, which consisted of 4 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. 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 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). Similarly, the percentage of tibia ash was increased by 600 U kg−1 PHY A supplementation (P<0.05). The requirement of nPP for maximal ADG and highest percentage tibia ash both was 0.40%. The phosphorus equivalency value of PHY A was estimated as 685 U kg-1 for male yellow broilers of 22- to 42-d-old age.