Determining the equivalent phosphorus released by an Escherichia coli-derived phytase in broiler chicks

Abstract

Seven-day-old male Ross 308 broiler chicks were used in a 14-d experiment to determine the equivalency value of a new phytase using corn-soybean meal based diets. The experimental diets consisted of positive control (PC) or negative control (NC) diets which were formulated to contain 5.0 or 1.2 g kg-1 non-phytate P, respectively, with a total P of 7.7 or 3.9 g kg-1, respectively; and respective calcium levels of 10.0 or 7.6 g kg-1. The test diets were formulated by the addition of monosodium phosphate (MSP; analyzed to contain 224.0 g kg-1 P) to the NC diet to supply 0.5, 1.0, or 1.5 g of P kg-1 diet, and phytase was added to the NC diet at 500 FTU or 1000 FTU kg-1 at the expense of corn starch. Each diet was randomly assigned to eight cages of four birds each. Body weight gain (BWG) showed both linear and quadratic increase (P < 0.05) with increasing level of dietary P or phytase supplementation (450 to 656 or 603 g, respectively). Feed efficiency (g BWG/g feed intake) increased linearly (P < 0.05) with increase in P or phytase supplementation and quadratic effect to increasing level of phytase (P < 0.05) supplementation (0.699 to 0.793 or 0.758 g, respectively). Percent tibia and toe ash increased linearly (P < 0.05) in response to supplemental P from MSP or phytase supplementation (37.7 and 8 to 47.9 and 10.9 or 45.2 and 10, respectively). Total intestinal tract P and N digestibility increased linearly (P < 0.05) with increasing P supplementation and showed increased (linear and quadratic, P < 0.05) response to phytase. The response variables, BWG, toe and tibia ash, feed intake and final body weight were used for P equivalency calculation. By solving the equated linear regression equations for the supplemental inorganic P intake and supplemental phytase intake for each of the response variables, between 0.930 and 1.101 g of P was released by 1000 FTU of phytase. The results of this study showed that this phytase was efficacious in hydrolyzing phytate P for bone mineralization and growth of broiler chicks. Key words: Chicks, equivalency value, monosodium phosphate, phosphorus, phytase