Impact of non-starch polysaccharides in broiler diets

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Despite vast research into the benefits and anti-nutritional effects of non-starch polysaccharides (NSP), and ubiquitous application of feed NSP-ase strategies in commercial diets, the majority of commercial nutritionists do not take dietary NSP levels into consideration when formulating poultry diets. The first component of this project involved a survey to understand current NSP levels in commercial poultry diets, and examining the relationship between these NSP levels and feed conversion ratios in commercial birds fed these diets.

The physiological functions of NSP are defined by whether they are water soluble or insoluble. The water soluble fraction is of particular interest in poultry diets, as the presence of soluble NSP (sNSP) increases digesta viscosity, which can have a negative impact on nutrient utilisation and excreta consistency. Furthermore, sNSP are readily fermentable, providing fuel for beneficial microbiota species and resulting in production of short-chain fatty acids (SCFA) that are a source of energy. The presence of sNSP also manipulates the gastrointestinal environment, making it unfavourable for pathogenic bacteria, enhancing gastrointestinal health and reducing competition between these bacteria and the host for expensive nutrients. Consequently, it is important to understand the quantity and composition of sNSP in poultry diets. The second component of this project examined the influence of the sNSP level in commercial-type wheat, corn, sorghum or barley-based diets on performance, apparent metabolisable energy, litter and excreta dry matter content, and total NSP degradability.

Supplementation of phytase and xylanase is ubiquitous in commercial poultry diets in Australia, and the use of beta-glucanases has become more widely accepted, but there are a wide range of other NSP-ases potentially being under-utilised. The third component of this project investigated whether other NSP-ases can increase the efficacy of xylanase. This was tested by exposing different batches of wheat, corn, sorghum, barley, canola meal and soybean meal to a two-step in vitro model that mimicked gastric and intestinal phase conditions, in the presence of no enzymes, the commercial recommended dose of xylanase, a double dose of xylanase, or xylanase coupled with β-glucanase, cellulase, pectinase, mannanase, galactanase or arabinofuranosidase. The quantity and size of xylo-oligosaccharides (XOS), derived from hydrolysing long-chain xylans into short-chain sugars, was determined, as the indicator of xylanase efficacy.

Recently there has been increased interest in application of NSP-ase cocktails into poultry diets, as a tool to combat the anti-nutritional effects of multiple polymers, enhance the efficacy of xylanase, and increase the quantity and variety of prebiotic oligosaccharides generated, which can provide fuel for a range of beneficial probiotic bacteria species. However, to date, there has been a lack of research into the efficacy and mechanisms of NSP-ase cocktails, namely how different NSP-ases cooperate. The economic benefits of using an NSP-ase cocktail compared with using xylanase, or potentially an increased dose of xylanase, is also poorly understood. Consequently, the fourth component of this project compared the efficacy of an NSP-ase cocktail with that of a commercial dose of xylanase and a double dose of xylanase, by examining their effect on broiler performance and meat yield, litter, digesta and excreta dry matter content, ileal nutrient digestibility and viscosity, caecal SCFA and microbiota composition, ileal XOS concentration, and NSP degradability along the gastrointestinal tract.

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