LAUSR

Abstract The objective of this study was to investigate how xylanase-induced changes in soluble sugar, short chain fatty acid (SCFA) and microbial content of the gut might be linked to broiler performance. A 42-day experiment was conducted using 328 male Ross 508 broiler chicks divided into two treatment groups, fed wheat-based diets with or without xylanase (0 or 16,000 BXU/kg). Each group had 8 replicate pens (13 birds per pen), with 3 additional replicate sampling pens per treatment (20 chicks per pen). Early body weight differences were shown, with xylanase-fed birds being 21 g ( P  = 0.02) and 39 g ( P  = 0.10) heavier at days 11 and 21 than control birds. Over the entire 42 day experimental period, body weight gain (BWG) and feed conversion ratio (FCR) with xylanase supplementation were not significantly different from the control, possibly due to the high performance of birds in both treatments. Xylanase supplementation increased ( P   0.05) soluble arabinose and xylose residues in the ileum and decreased ileal viscosity of birds at all ages, suggesting arabinoxylan degradation to soluble oligosaccharides. Xylanase had no significant effect on soluble sugar residue concentration in the caecum at any age. Irrespective of treatment, caecal soluble sugar residue content was considerably higher in 11 day-old birds, possibly illustrating poorer nutrient digestion and absorptive capacity of young birds. The proportion of xylose and arabinose residues in total caecal soluble sugars decreased ( P   0.001) at day 21, suggesting greater utilisation by resident bacteria. At day 42, compared to the controls, xylanase-fed birds had higher ( P  = 0.01) Bifidobacterium spp. levels (5.7 e +10 versus 8.1 e +9 ), increased quantities of acetic ( P  = 0.002) and butyric acids (P  P  = 0.03) lactic acid levels in the caeca. At all ages, xylanase treatment reduced ( P  = 0.04) the proportion of branched chain volatile fatty acids in total SCFA, suggesting a reduction in protein fermentation. These findings suggest that greater degradation of wheat arabinoxylan with xylanase can enhance colonisation of specific bacteria and production of SCFAs in the caeca, an event that may relate to improved broiler performance.