1. The objective of this study was to examine the influence of dietary soluble non-starch polysaccharide (sNSP) level and xylanase supplementation on productive performance, viscosity and pH along the gastrointestinal tract in laying hens. Excreta moisture content, ileal and caecal microbiota and short-chain fatty acid (SCFA) composition and apparent total tract nutrient utilisation were measured.

2. Hyline Brown laying hens (n = 144) were housed individually at 25 weeks of age and allocated to one of the four wheat-based dietary treatments in a 2 × 2 factorial arrangement, consisting of two levels of sNSP (High 13.40 g/kg or Low 11.22 g/kg), with or without xylanase (0 or 12,000 BXU/kg). Birds were fed the dietary treatments for 56 d.

3. Increasing dietary sNSP increased jejunum viscosity, degradability of total NSP, total tract flow of insoluble arabinose, and succinic acid concentration in the caeca (P < 0.05). Feeding high sNSP decreased excreta moisture content, total tract energy retention and free oligosaccharide, total tract flow of soluble and insoluble galactose and insoluble rhamnose and fucose, and ileal acetic and lactic acid concentrations (P < 0.05), and tended to reduce egg production (P = 0.058).

4. Supplementation with xylanase resulted in reduced jejunum and ileum viscosity, caecal pH, excreta moisture, flow of soluble arabinose and glucose and insoluble arabinose and xylose, caecal concentration of Lactobacillus sp. and isobutyric and succinic acid, and ileal concentration of Bacillus sp. and total anaerobic bacteria (P < 0.05). Xylanase application also increased energy retention and insoluble and total NSP degradation, and caecal abundance of Bifidobacteria sp. and valeric acid (P < 0.05).

5. These results reiterated the ability of xylanase to improve nutrient digestibility and reduce excreta moisture content in laying hens, and highlighted the importance of considering dietary sNSP level in laying hen diets.

Necrotic enteritis (NE) is an enteric disease of poultry caused by Clostridium perfringens (C. perfringens). The incidence of NE has increased in several countries as a result of restrictions on the use of in- feed antibiotics. This disease may be triggered by a combination of coccidiosis and the presence of undigested nutrients in the hindgut providing nutrients and high pH that favour the proliferation of patho-gens. Meat and bone meal (MBM) inclusion rates above 4% and higher dietary calcium (Ca) inclusion rates above 1.0% may potentially favour the overgrowth of enteric pathogens, including C. perfringens. High levels of elastin, collagen and keratin from MBM are refractory to gastric digestion and may act as nutrient substrates for C. perfringens. Such proteins are metabolised by C. perfringens by putrefactive fermenta-tion, producing trimethylamine and ammonia, that affect gut health and increase the pH of digesta. Digesta pH may become elevated by feeding a diet high in Ca, as this nutrient has a high acid-binding capacity. Calcium interacts with phytic acid, forming mineral-phytate complexes that decrease the activity of exogenous dietary phytase. This reduces digestion and increases the influx of nutrients into the hindgut. Similarly, smaller particle sizes (dgw <75 μm) and high solu-bility of some Ca sources could increase digesta pH and chelation of Ca by phytic acid and decrease nutrient digestibility. Whether the practice of overfeeding Ca in order to ensure this nutrient is not limiting for bone development may be putting the bird at risk of a NE outbreak is not known. This review discusses the potential for dietary MBM to exacerbate NE in broiler chickens. The impact of Ca level and particle size to affect gut pH and phytase efficacy are discussed, with inferences to alter the onset of NE.

This study was to examine if it is possible to accelerate sorghum digestion in broiler chickens by targeting fermentation of the xylan. Cobb 500 broilers (n = 960, 80 birds per treatment) were fed 12 sorghum-soybean meal-based dietary treatments fed as 3 phases (starter d 0 to 12, grower d 13 to 23, finisher d 24 to 35), with 8 replicate pens of 10 birds per treatment. For half of the treatments (n = 6), 10% of the sorghum in the diet was directly replaced with 10% wheat bran, as a source of fermentable fibre. The diets were supplemented with either 0, 50 or 2,000 mg/kg xylo-oligosaccharides (XOS), with or without xylanase application. Body weight gain (BWG), feed intake (FI) and feed conversion corrected for mortality (cFCR) was determined at d 0 to 35, and male and female body weight were measured on d 35. On d 35, ileum and caeca samples were collected from 2 birds per pen, for determination of caecal cellulase and xylanase activity, microbiota composition and short chain fatty acid (SCFA) concentration, and ileal XOS concentration. Supplementation with 2,000 mg/kg XOS caused increased BWG at d 0 to 35 (P = 0.007) and enhanced caecal propionic, valeric and succinic acid concentration (P < 0.05). Wheat bran increased FI (P = 0.018) and BWG (P = 0.016), as well as caecal Bifidobacteria concentration (P < 0.001). Ileal XOS concentration was greatest when feeding combined wheat bran, 2,000 mg/kg XOS, and xylanase, resulting in increased caecal total SCFA, acetic acid and butyric acid concentration, and xylanase and cellulase activity (P < 0.05). Results from this study present that feed efficiency in birds fed sorghum-based diets is improved as a consequence of supplementing with fermentable fibre, xylanase and XOS.