Effect of dietary enzyme on the metabolizable energy of diets with increasing levels of barley fed to broilers at different ages

The effect of enzyme addition on the AMen of a two-row barley for broiler chickens was determined with increasing levels of barley at 10 and 30 days of age in a 4 × 3 factorial design. Four levels of barley (30, 40, 50 and 60%) and two commercial enzyme complexes were used, the first obtained from Trichoderma reesei and Aspergillus niger and the second from Bacillus subtilis and Humícola insolens. At both 10 and 30 days of age, the AMEn of diets decreased significantly with increasing barley level (218 kJ for each 10% barley included). The enzyme response magnitude (1.4% on average) was affected by barley level; the response was only significant at 40 and 50% barley inclusion (AMEn improved 2.6% on average). There was no difference between enzyme complexes or ages in the AMEn of the diets or the barley (AMEn 12.71 and 13.10 MJ kg−1 for unsupplemented and enzyme supplemented barley respectively). Gut viscosity alone accounted for 97% of AMEn variation among unsupplemented diets. Increasing gut viscosity by 1 cps corresponded to a decrease in AMEn of 59 kJ. However, gut viscosity was not highly related to AMEn in enzyme supplemented diets because of the virtual complete elimination of the viscosity effect.