Nutrient utilisation and growth performance responses of White Pekin ducks (Anas platyrinchos domesticus) offered diets containing lowor high-viscosity wheat supplemented with xylanase were investigated in two studies. In Expt 1, six diets consisting of low-viscosity wheat or high-viscosity wheat supplemented with 0·0, 1·5 or 3·0 g xylanase (2590 units/g)/kg diet were used in a true metabolisable energy (TME) bioassay with eight 8-week-old ducks per diet group. In Expt 2, eight pens of ten

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... ld ducks per pen for each of six wheatbased diets arranged in a 2 £ 3 factorial of low-viscosity or high-viscosity wheat and 0·0, 1·5 or 3·0 g xylanase/kg were used in a 42 d growth study. High-viscosity wheat depressed (P, 0·001) TME and xylanase supplementation improved (P,0·001) TME, more so for high-viscosity than low-viscosity wheat. Xylanase supplementation of the high-viscosity wheat-based diet improved (P, 0·05) weight gain and gain:feed ratio by 13 and 12 % respectively. There was no weight gain or gain:feed ratio response to xylanase supplementation of the low-viscosity wheat-based diet. Xylanase supplementation reduced (P, 0·001) the viscosity of duodenal and ileal digesta for highviscosity but not low-viscosity wheat-based diets. Ileal digestibilities of nutrients and energy were higher (P, 0·001) for low-viscosity than high-viscosity wheat-based diets; xylanase supplementation improved (P, 0·05) energy, fat, N and starch digestibilities. Given that xylanase supplementation of high-viscosity wheat assuaged its anti-nutritional effect, it is surmised that digesta viscosity plays a role in antinutritional effects in wheat-based diets for ducks. White Pekin ducks: Wheat: Xylanase: Viscosity: Nutrient digestibility * Corresponding author: Professor Olayiwola Adeola, fax þ 765 464 9346, email ladeola@purdue.edu Abbreviations: TME, true metabolisable energy; TMEn, true metabolisable energy corrected for nitrogen.