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

Four digestibility trials using broilers from 12 to 21d or 7 to 21d 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 100g/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 (AME_n) 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 (13.61MJ/kg) and PXA (13.70MJ/kg) increased the AIDE (P<0.05) compared to the control diets (13.29MJ/kg). XA increased (P<0.05) AME_n (12.89MJ/kg) compared to the control diets (12.61MJ/kg), and PXA further increased it (13.00MJ/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 AME_n and the addition of protease on top of carbohydrases further increased AID of AA and AME_n in young broilers fed maize-SBM diets without or with maize-DDGS.