The Role of Soluble Non-Starch Polysaccharides in Poultry Diets

Abstract

<p>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.</p> <p>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.</p> <p>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.</p> <p>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. </p>