Eggs 2007

Efficacy of Phytases on Egg Production and Nutrient Digestibility in Layers Fed Reduced Phosphorus Diets
N. Liu,* G. H. Liu,† F. D. Li,*1 J. S. Sands,‡ S. Zhang,† A. J. Zheng,† and Y. J. Ru§
*Faculty of Animal Science and Technology, Gansu Agricultural University, Lanzhou, China, 730070; †Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, China, 100081; ‡Danisco AnimalNutrition, Marlborough, Wiltshire, SN8 1XN, United Kingdom; and §Danisco Animal Nutrition, Science Park III, Singapore, 117525 ABSTRACT The effects of phytases on the performance of layers and the ileal nutrient digestibility of corn-, soybean-, and by-product meal-based diets were assessed with 320 Hy-Line brown layers from 23 to 28 wk of age. Layers were grouped randomly into 5 treatments, with 8replicates per treatment and 8 layers per replicate. The 5 diets consisted of a positive control diet with adequate Ca (3.30%), total P (0.50%), and nonphytate P (NPP; 0.28%), and a negative control diet with Ca reduced by 0.12%, total P reduced by 0.14%, NPP reduced by 0.13%, and 3 phytases (phytase A derived from Aspergillus niger, and phytases B and C derived from Escherichia coli)supplemented at 300 phytase units/kg of feed, respectively. Egg production and feed intake were recorded daily, and eggshell quality and ileal nutrient digestibility were measured at the end of a 6-wk feeding period. The results revealed that the reduction of Ca and P from the positive control diet significantly depressed feed intake, egg mass, eggshell hardness, and the digestibility of N, Ca, P, and aminoacids (P < 0.05). Phytase supplementation in the negative control diet improved the digestibility of P and Ca by 11.08 and 9.81% (P < 0.05), respectively, whereas it improved the digestibility of amino acids by 2 to 8% (P < 0.05). However, the digestibility of most amino acids was not restored to the levels of the positive control diet by the application of phytases. Supplementing phytases in thenegative control diet improved the rate of lay, egg mass, and egshell quality to the levels of birds fed the positive control diet. These results suggest that supplementing phytases can improve the digestibility not only of Ca and P, but also of amino acids in layers fed a corn-, soybean-, and by-product-based diet.

Key words: phytase, nutrient, digestibility, layer 2007 Poultry Science86:2337–2342 doi:10.3382/ps.2007-00079

INTRODUCTION
Phytate exists widely in feed ingredients and is poorly degradable in the gastrointestinal tract of poultry because of the lack of endogenous phytase. Its presence in poultry feed ingredients restricts the effective use of organic P and other nutrients, including Ca, energy, and amino acids, in the alimentary tract (Cheryan, 1980; Ravindran et al.,1995). This is due to the chelation of Ca (Vohra et al., 1965; Oberleas, 1973; Cheryan, 1980), amino acids (De Rham and Jost, 1979), and starch (Ravindran et al., 1999) by phytate. This antinutritional effect was demonstrated in broilers, in which the digestibility of energy and amino acids declined with an increase in dietary phytate (Ravindran et al., 2006). Although it has been well documentedthat phytase hydrolyzes phytate and increases the digestion of P, consequently reducing the excretion of P and

©2007 Poultry Science Association Inc. Received February 15, 2007. Accepted August 4, 2007. 1 Corresponding author: lifd@gsau.edu.cn

lowering environment pollution, the use of phytase as a tool to improve amino acid and energy utilization has not been sufficiently demonstrated.Recently, several studies have demonstrated that the application of phytase to conventional diets improves the digestion of energy and amino acids in broilers (Rutherfurd et al., 2004; Onyango et al., 2005; Cowieson et al., 2006b). Based on a large amount of data, the matrix value of phytase has been developed to optimize profits in the broiler production system (Shelton et al., 2004; Partridge, 2006;...