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.

Calcium forms the bulk of minerals added to poultry diets. It is chelated by phytic acid and forms phytate-mineral complexes reducing Ca availability and the ability of phytase enzyme to hydrolyse phytate. High dietary Ca has been implicated in the pathogenesis of necrotic enteritis as it increases gut pH and buffering capacity and decreases uptake of other nutrients. It was hypothesised that high dietary calcium and phytase would favour the proliferation of Clostridium perfringens.

This study investigated the influence of meat and bone meal (MBM), phytase, and antibiotics (AB) on the performance, intestinal pH, ileal digestibility, cecal microbiota, and tibial mineralization in Ross 308 broilers challenged with necrotic enteritis (NE). A total of 672-day-old male Ross 308 chicks were allocated to 8 treatments with 6 replicate pens, with 14 birds each. The study employed a 2 × 2 × 2 factorial arrangement of treatments: MBM (no or yes), AB (no or yes, zinc bacitracin + salinomycin), and phytase level (500 or 1,500 FTU/kg; both using 500 matrix recommendations). Diets were based on wheat-soybean meal-canola meal. All birds were challenged with Eimeria spp on day 9 and Clostridium perfringens (C. perfringens) strain EHE-NE18 on day 14 and day 15. On day 21 (postchallenge), birds fed MBM had reduced weight gain (WG; P < 0.05) relative to without MBM. A 2-way phytase × AB interaction for WG on day 14 (P < 0.001) and day 21 (P < 0.001) and feed conversion ratio on day 21 (P < 0.001) and day 42 (P < 0.01) indicated positive effects of high phytase on bird performance in the presence of AB. On day 42, a 3-way MBM × phytase × AB interaction (P < 0.01) was observed for WG, showing high phytase increased WG with AB, relative to the birds without AB in the presence of MBM. A 2-way MBM × phytase interaction (P < 0.01) was observed for apparent ileal digestibility of Ca and P on day 16, whereby there was a notable reduction in Ca and P digestibility in birds fed MBM-free diets and a low phytase level, but with the high phytase level, Ca and P digestibility was not influenced by MBM. In conclusion, in NE challenged birds, high phytase has a beneficial effect on leg health and mineral utilization to the extent that it can replace MBM and has beneficial effects on bird performance in the presence of AB.

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.

The majority of poultry diets are now plant-based, meaning they contain approximately 10% fibre, primarily in the form of non-starch polysaccharides (NSP). NSP level and composition directly influences gastrointestinal health and nutrient utilisation, in both meat chickens and laying hens. Of particular interest is the influence of the water-soluble fraction of NSP in poultry diets. Soluble NSP (sNSP) can induce anti-nutritional effects if it is in a form capable of increasing digesta viscosity, thereby impeding nutrient absorption and causing issues with sticky excreta. However, sNSP also has beneficial effects, in that it is readily fermentable and acts as an energy source, stimulating beneficial microorganisms and manipulating gastrointestinal conditions, including pH, to generate undesirable conditions for pathogenic bacteria. The effects of sNSP are dependent on solubility, molecular weight, and configurations of the polymers in the gastrointestinal environment. This thesis examines the degree of influence that dietary sNSP in commercial-type diets has on performance and gastrointestinal health in meat chickens and laying hens.

Firstly, the influence of dietary sNSP level in corn- and wheat-based diets, in the absence of exogenous enzymes, on growth performance, nutrient utilisation, NSP degradability and the intestinal environment in broilers was evaluated. The results from this study showed that birds require a source of fermentable fibre to optimise the gastrointestinal environment, in terms of pH, viscosity and a desirable microbial profile. This facilitates production of SCFA, which act as a source of energy, and inhibits proliferation of pathogenic bacteria, increasing bird health and performance. It is possible to achieve this by ensuring sufficient, but not excessive, quantities of sNSP are formulated into the diet. It is especially important to consider this for young birds, of which the microbiota can be modulated and managed. It appears to be particularly important to consider sNSP level when formulating wheat-based diets for broilers, although it is vital to ensure there is adequate fermentable fibre available in NSP-poor-based diets.

Secondly, the impact of sNSP level on xylanase efficacy in laying hens was investigated. Application of xylanase into laying hen diets positively influenced the gastrointestinal environment, namely gut viscosity, caeca pH, total tract flow and disappearance of dietary NSP and ileal and caecal microbiota composition. The consequence of this was enhanced energy utilisation and lower excreta moisture content. Increasing dietary sNSP level had a detrimental effect on nutrient utilisation. Dietary sNSP level directly influenced the efficacy of xylanase, namely its ability to promote the fermentation and utilisation of NSP to produce SCFA.

Overall, the outputs from this thesis likely reveal that dietary sNSP level has a direct impact on the gastrointestinal environment. This is primarily attributable to its role as a fuel for beneficial bacteria, and ability to induce an environment that is unfavourable for pathogenic bacteria. This project highlights the importance of considering sNSP level, and composition, when formulating poultry diets, with the aim of ensuring there is sufficient quantities available to induce these beneficial effects, but not an excessive level which will induce anti-nutritional effects on digesta viscosity. Further investigation is required into the optimum level of sNSP to formulate to depending on diet composition, for both meat chickens and laying hens.