Strategic use of carbohydrase enzymes in broiler diets to increase productivity by improving gut health

本项目旨在研究饲粮中添加糖酶（木聚糖酶和β -葡聚糖酶）在促进生长性能、肠道水平免疫和炎症反应、肠道细胞发育和完整性以及肠道微生物群变化方面的有益影响。据推测，高添加水平的碳水化合物酶将通过促进肠道健康而不仅仅是提高营养物质的利用来改善鸟类的生长性能。家禽的饮食以谷物和豆类为主。英国最重要的谷物是玉米、小麦和大麦。小麦和大麦含有大量的非淀粉多糖（NSP），这会降低动物对营养物质的利用，导致肠道中有害微生物的增殖，并损害肠道细胞的发育，从而损害动物的生长。在家禽日粮中添加碳水化合物酶是为了提高能量利用率，但它们也可能对肠道健康有益。例如，一项研究表明，在日粮中加入NSP水解产物（从谷物发酵中获得）可以减少肉鸡粪便中的沙门氏菌数量。NSP水解产物可以促进肠道健康，因为NSP水解产生的低聚糖可以作为益生元。然而，将NSP水解为谷物预处理，并将预处理后的谷物加入实际的日粮中，既不实际，也不可行。实际可行的途径是在饲粮中添加NSP酶，帮助将NSP水解产物输送到肉鸡肠道，从而刺激动物生长，增强肠道健康。因此，本博士项目将研究在饲粮中战略性地使用NSP酶来促进肠道健康和提高肉鸡生产力。项目的第一部分旨在展示NSP在体内水解的程度。据认为，NSP水解成较大的低聚糖具有刺激生长的作用，而较小的低聚糖则对消化道有益。然而，目前还没有系统的研究表明补充糖酶能在多大程度上促进活禽NSP的水解。利用高效液相色谱法，从消化道不同部位收集的食糜将被分析，以显示不同类型的NSP水解产物的相对丰度。NSP水解的数据将与生长性能和营养物质消化率数据联系起来，使研究与行业相关。后续的试验将设计研究各种可能的作用模式，通过糖酶提高生长性能和改善肠道环境。用组织学和形态学方法研究小肠吸收细胞的发育过程。NSP水解产物在调节肠道炎症和免疫反应中的可能作用将通过肠道炎症和免疫的分子标记进行研究。这些将与使用消化道形态学和分子反应以及血液中的化学标记物的细胞完整性测量相结合。在优化反应的酶产物的水平和组合之后，这些鸟将暴露于中度疾病挑战中，例如在典型的鸟群中可能发生的疾病挑战，鸟类对疾病挑战的反应将通过炎症，生长性能和营养利用反应以及肠道微生物种群的动态来研究。该项目属于BBSRC的研究范围，该研究展示了牲畜物种的营养与健康之间的联系。该项目将展示碳水化合物酶促进肉鸡生长性能和肠道健康的可能途径，因此研究将为营养-健康相互作用提供有价值的信息，从而促进酶的进一步发现。

The objective of the proposed project is study the beneficial effects of supplementing diets with carbohydrases (xylanase and beta-glucanase), in promoting growth performance, gut level immunity and inflammatory responses, intestinal cell development and integrity, and changes in gut microbial population. It is hypothesised that supplementation of carbohydrases at high supplemental levels will improve growth performance of birds via promotion of gut health rather than improved nutrient utilisation only. Poultry diets are based on cereal grains and legume meals. The most important cereal grains in the UK are maize, wheat and barley. Wheat and barley have high amounts of non-starch polysaccharides (NSP) which impair animal growth by reducing nutrient utilisation, causing proliferation of harmful microorganisms in the gut, and impair intestinal cell development. Carbohydrases are supplemented to poultry diets to increase energy availability, but they can have gut health benefits as well. For example, incorporation of NSP hydrolysis products (obtained from fermentation of grains) in diets is shown to reduce salmonella count in the droppings of broilers in a study. It appears that NSP hydrolysis products can promote gut health, because the oligosaccharides produced by NSP hydrolysis can act as prebiotics. However it is neither practical, nor feasible, to hydrolyse NSP as a cereal grain pre-treatment and incorporate the pre-treated cereal grains in practical diets. The practical and realistic route is the strategic dietary supplementation of NSP enzymes that can help deliver NSP hydrolysis products to broiler gut and thus stimulate animal growth and enhance gut health. Consequently this PhD project will investigate the strategic use of NSP enzymes in the diets to promote gut health and enhance broiler productivity. The first part of the project is designed to show the extent of NSP hydrolysis in vivo. It is thought that hydrolysis of NSP to larger oligosaccharides have growth stimulation effects whereas the smaller oligosaccharides have health benefits for the digestive tract. However, there have been no systematic study on the extent to which carbohydrase supplementation enhance NSP hydrolysis in live birds. Using HPLC, the digesta collected from different sections along the digestive tract will be analysed to show the relative abundance of the different types of NSP hydrolysis products. The data on NSP hydrolysis will be related back to growth performance and nutrient digestibility data to make the study industry-relevant.Subsequent experiments will be designed to study various possible modes of action by which carbohydrases elicit increased growth performance and improved gut environment. The cellular development of the absorptive cells in the small intestine will be study using histological and morphological measures. The possible roles of NSP hydrolysis products in modulating gut-level inflammatory and immune responses will be examined using molecular markers of gut inflammation and immunity. These will be combined with measurement of cellular integrity using both morphological and molecular responses in the digestive tract as well as chemical markers in the blood. After refining the level and combination of enzyme products that optimize responses, the birds will be exposed to moderate disease challenge such as can occur in a typical flock and the response of birds to the disease challenge will be studied using inflammatory, growth performance and nutrient utilisation responses, as well as the dynamics of gut microbial population. The project falls within the remit of BBSRC research demonstrating the link between nutrition and health of livestock species. The project will demonstrate possible ways by which carbohydrases promote growth performance and gut health in broilers and the studies will thus provide valuable information on nutrition-health interaction which can stimulate further enzyme discovery.