Beneficial effects of xylanase and/or phytase inclusions on ileal amino acid digestibility, energy utilisation, mineral retention and growth performance in wheat-based broiler diets

The effects of individual and combined inclusions of xylanase and phytase in broiler diets based on a characterised wheat were evaluated. The positive control diet was formulated to be adequate for phosphorus (P) with 3.8gkg⁻¹ nonphytate P and the low-P, negative control diet contained 2.6gkg⁻¹ nonphytate P. The negative control diet was supplemented with xylanase (2000XUkg⁻¹), or phytase (500FTUkg⁻¹), or xylanase plus phytase (2000XUkg⁻¹ and 500FTUkg⁻¹). Treatment effects on ileal digestibility of amino acids, energy and nitrogen utilisation, ileal digestibility and total tract retention of minerals, toe ash content and the growth performance were determined. In combination, xylanase plus phytase increased mean apparent ileal digestibility (AID) coefficients of 17 amino acids by 8.6%, which exceeded the increases of 4.8% and 5.5% generated by xylanase and phytase, respectively. Increases in AID were significant (P<0.05) for the majority of amino acids in response to enzyme inclusions with indications of synergistic responses for five amino acids. Xylanase plus phytase increased (P<0.05) nitrogen-corrected AME by 0.63MJkg⁻¹, ileal energy digestibility by 0.89MJkg⁻¹ and energy AID coefficient by 6.7% relative to the negative control diet. The enzyme combination increased (P<0.05) coefficients of ileal nitrogen digestibility by 9.1% and 8.0% relative to positive and negative control diets, respectively. Phytase increased (P<0.05) ileal calcium digestibility by 32.2% and ileal P digestibility by 28.0% relative to the negative control. Also, phytase increased (P<0.05) the AID coefficient of sodium to -0.038 from -0.516 in the negative control diet and the combination increased the same coefficient to 0.043. P reduction in the control diet lowered (P<0.05) bone mineralisation, but toe ash contents were restored by phytase and xylanase plus phytase. P status of the control diets had no effect (P>0.05) on the efficiency of feed conversion, but xylanase (6.2%), phytase (2.5%) and xylanase plus phytase (3.9%) enhanced (P<0.05) feed efficiency relative to the negative control. The low-P diet depressed (P<0.05) weight gain and feed intake but phytase and xylanase plus phytase restored both weight gain and feed intake. Overall, the present data indicate that the simultaneous inclusion of xylanase plus phytase in wheat-based broiler diets was beneficial in terms of nutrient utilisation and growth performance.