Title: Effects of Increasing Concentrations of Maize-Expressed Non-Starch Carbohydrase Enzyme on Broiler Growth Performance and Ileal Nutrient Digestibility
Abstract: Background and Objective: An experiment (phase 1) was conducted to evaluate the retained activity of a maize-derived, recombinant carbohydrase enzyme (AC1) when exposed to heat during the pelleting process and homogeneity when mixed into mash diet.A second experiment (phase 2) was conducted to evaluate the effects of increasing AC1 concentrations on male broiler growth performance and ileal nutrient digestibility.Materials and Methods: A total of 728 broilers were randomly assigned to seven dietary treatments with each treatment consisting of 13 replicates with eight Cobb 500 male broilers.The experimental design included a positive control (PC), a reduced energy negative control (NC, comprising the PC less 132 kcal kgG 1 ) diet and five additional treatments with increasing dose of AC1 (5, 50, 100, 250 and 500 U glucanase kgG 1 ) added to the NC diet.Birds were fed a starter ration for the duration of the study (16 d).Average body weight (BW), mortality adjusted feed conversion ratio (FCR) and feed consumption (FC) were determined on 16 d of age.At the conclusion of the experiment, all birds from each replicate pen were necropsied and ileal contents pooled within replicate to determine ileal digestibility of energy (IDE) and nitrogen (IDN).Results: In Phase 1, the recovery of ß-glucanase activity in the pellets (in relation to mash feed) were 111, 83 and 82% when pelleted at 80, 85 and 90EC, respectively.The coefficient of variation of glucanase recovered when AC1 was mixed into feed and was less than 10%.In Phase 2, the inclusion of AC1 at 100 and 250 U glucanase kgG 1 increased (p<0.01)BW compared to both the PC and NC fed broilers.This elevation in BW was related to an increase (p<0.01) in FC.As expected, reducing energy in the NC diet decreased (p<0.01)IDE value of the feed as compared to the PC diet.The addition of AC1 to supply $100 U glucanase kgG 1 increased (p<0.01)IDE compared to the NC diet and restored IDE equivalent (p>0.05) to the PC diet.Regression analysis confirmed linear and quadratic increases in IDE and IDN with the addition of AC1.Conclusion: These data demonstrate the thermal stability of maize-derived, recombinant AC1 and that increasing levels positively influences nutrient digestibility leading to significant improvements in broiler performance.