Animal Feed Science and Technology 129 (2006) 149–158 Using the precision-feeding bioassay to determine the efficacy of exogenous enzymes—A new perspective A.J. Cowieson a,* , T. Acamovic a , M.R. Bedford b,1 a Avian Science Research Centre, SAC, Ayr, KA6 5HW, UK b Danisco Animal Nutrition, Marlborough, Wiltshire, SN8 1XN, UK Abstract The effect of the ingestion of exogenous enzymes on the excretion of endogenous material from the GI tract of broiler chickens that had been denied access to feed was investigated. Fifty-six female Ross broilers with a mean body weight of approximately 2.6 kg were used in a modified precision-feeding study. The birds received a solution of glucose supplemented with protease, -amylase, phytase, xylanase, pectinase or cellulase or glucose with no supplemental enzymes and nutrient excretion over the subsequent 48-h period was measured. The ingestion of pectinase and protease increased (P<0.05) the excretion of endogenous amino acids, energy and dry matter compared to birds fed glucose. The excretion of sialic acid was greater (P<0.05) from birds which received glucose supplemented with pectinase than from birds fed glucose alone, suggesting changes in mucin secretion. It can be concluded that some exogenous enzymes can increase the excretion of endogenous material from broiler chicks in a precision-feeding system. The fact that these enzymes have been shown to enhance growth rate in long-term studies suggests that the ability of short-term precision-feeding studies to predict enzyme response in longer-term growth studies may be compromised. © 2005 Elsevier B.V. All rights reserved. Keywords: Broilers; Endogenous loss; Enzymes; Precision-feeding * Corresponding author at: Danisco Animal Nutrition, Marlborough, Wiltshire, SN8 1XN, UK. E-mail address: aaron.cowieson@danisco.com (A.J. Cowieson). 1 Current address: Syngenta Animal Nutrition, Chestnut House, Beckhampton, Wiltshire, SN8 1QJ, UK.