Comparative effects of dietary carbohydrases without or with protease on the ileal digestibility of energy and amino acids and AMEn in young broilers

Four digestibility trials using broilers from 12 to 21 d or 7 to 21 d of age were conducted to evaluate the nutrient digestibility responses of two enzyme combinations when supplemented to maize–soybean meal (SBM) based diets without (trials 1 and 3) or with (trials 2 and 4) 70 or 100 g/kg maize dried distillers grain with solubles (DDGS). Apparent ileal digestible energy (AIDE), apparent ileal digestibility (AID) of amino acids (AA), total tract apparent retention (TTAR) of nitrogen (N) and N-corrected apparent metabolisable energy (AMEn) were assessed. In each trial, a control diet and the control diet supplemented with an enzyme complex containing xylanase and amylase (XA) or one containing protease, xylanase and amylase (PXA) were tested. Trials 1 and 2 had six replicate cages per treatment, with six birds per cage; and trials 3 and 4 had eight replicate cages per treatment, with five birds per cage. Data were analysed by ANOVA for each trial, as well as a combined dataset, which model included the main effects of maize-DDGS inclusion, dietary enzyme and trial site and all two-way interactions. Across trials, both XA (13.61 MJ/kg) and PXA (13.70 MJ/kg) increased the AIDE (P<0.05) compared to the control diets (13.29 MJ/kg). XA increased (P<0.05) AMEn (12.89 MJ/kg) compared to the control diets (12.61 MJ/kg), and PXA further increased it (13.00 MJ/kg) compared to XA. Supplementation with XA had no effect on the AID of AA, whereas PXA increased the AID of nitrogen and all AA (P<0.05) except methionine. The AA with the greatest response to PXA were cysteine (+5.4%), threonine (+4.4%), glycine (+3.6%) and valine (+3.3%). The least responsive AA to PXA inclusion were methionine (+1.0), glutamine (+2.0), lysine (+1.9%) and arginine (+2.2%). Irrespective of the AA, PXA increased AID of AA as a proportion of the ileal undigested fraction of AA in the control diets by 12–13%. Supplemental xylanase and amylase increased AIDE and AMEn and the addition of protease on top of carbohydrases further increased AID of AA and AMEn in young broilers fed maize–SBM diets without or with maize-DDGS.