Accounting for the effects of interactions between Phosphorous, Calcium and exogenous phytase on pig dietary requirements and performance

该项目解决了BBSRC的战略重点：与动物部门相关的农业和粮食安全，特别是生物技术应用于动物饲料的优先事项。本试验旨在研究外源植酸酶与猪饲料中磷、钙含量在猪消化道中的相互作用，从而提高猪饲料的利用率。这将在现有模拟模型的背景下完成，该模型支持决策支持工具（DST），以减少P排泄并改善英国生长和育肥猪的生长。众所周知，钙和磷都具有重要的骨骼和生理功能。同时，由于植物性饲粮磷的消化率较低，因此需要添加昂贵的无机磷，磷是猪日粮中第三昂贵的成分。从环境的角度来看，磷的供应是有限的，不可再生的，饲料转化效率低导致粪便中水溶性磷的大量排泄，导致水体污染以富营养化的形式出现。该行业，如AHDB猪肉，认识到在确保维持猪的生产性能和健康的同时减少磷排泄的重要性，并已参与研究以实现这些目标。大多数植物性磷以及猪饲料中的大部分磷都与植酸盐分子结合。这种形式的磷不易被非反刍动物消化，因为它们不能产生足够水平的内源性植酸酶来进行植酸去磷酸化。一种日益流行的提高植物基磷生物利用度的方法是通过补充外源植酸酶。外源性植酸酶水解植酸分子释放无机磷，然后可被动物吸收。据估计，添加外源植酸酶可使磷排泄量减少30-60%，从而降低猪日粮中磷的添加水平。然而，为了充分了解目前的问题，必须同时研究磷和钙的消化、吸收和排泄，因为这两种主要的常量矿物质在猪的消化道中是相互依存和相互作用的。从历史上看，Ca并没有像P那样引起那么多的学术兴趣，Ca被认为是影响植酸-P生物利用度的最被低估的因素。这主要是由于无机钙补充剂价格便宜且易于获得，并且过量的钙排泄不会明显引起任何环境问题。很少有研究试图在消化率的基础上分离钙磷比的影响，消化率考虑的是营养物质的内源性损失，而不是饲料成分中的总浓度。在过去的10年里，该行业一直以总钙：可消化磷比例（2:1）为基础配制饲粮。根据可消化钙和可消化磷的比例来配制饲粮，对于更有效地减少磷排泄至关重要。数学模型可以被视为研究磷保留和排泄的有用工具，包括影响这些过程的钙水平和植酸酶补充等因素，并且通常可以进行许多在体内不可能进行的计算机实验。开发一种新的数学模型来解释钙和磷之间的相互作用，应该为全面减少磷造成的环境影响的实践提供信息，并有助于最大限度地提高养猪业对养分的利用。新模型和DST旨在准确预测钙的消化率及其对动物排泄和生长的影响。在模型中模拟可消化钙的命运将导致更准确地预测磷排泄的减少和磷对生长的利用。迄今为止，任何先前的模型都没有实现这一目标。

The project addresses BBSRC Strategic Priority: Agriculture and Food Security relating to the Animal Sector, and in particular the priority of Biotechnologies as applied to animal feed. It aims to investigate the interactions in the digestive tract of the pig between exogenous phytase and Phosphorous (P) and Calcium (Ca) contents in pig feed in order to lead to a better feed utilisation. This will be done in the context of an existing simulation model that supports a Decision Support Tool (DST) to reduce P excretion and improve growth in growing and finishing pigs in the UK. Both Ca and P are well-known to have important skeletal and physiological functions. At the same time, P is the third most expensive component in pig diets due to the low digestibility of plant dietary P and the consequent need to supplement with expensive inorganic P supplements. From an environmental point of view, P supplies are limited and non-renewable and low feed conversion efficiency leading to the high excretion of water-soluble P in manure causes water pollution in the form of eutrophication. The Industry, e.g. AHDB Pork, recognises the importance of reducing P excretion whilst ensuring that pig performance and health are maintained, and has been involved in research to achieve these objectives. The majority of plant based P and hence most P in pig feed is bound to the phytate molecule. This form of P is poorly digested by non-ruminant animals as they do not generate sufficient levels of endogenous phytase required for phytate dephosphorylation. One, increasingly popular way of improving bioavailability of plant based P is through supplementation of exogenous phytase. Exogenous phytase hydrolyses the phytate molecule to release inorganic P, which can then be absorbed by an animal. It has been estimated that exogenous phytase supplementation can lead to 30-60% reduction of P excretion, which would permit lower levels of supplement of P in pig diets. However, in order to fully understand the problem at hand, digestion, absorption and excretion of P must be studied simultaneously with Ca, as these two major macrominerals are interdependent and interact in their utilisation by the pig in its digestive tract. Historically, Ca has not generated as much academic interest as P and Ca is considered to be the most underestimated factor contributing to phytate-P bioavailability. This is mostly due to the fact that inorganic Ca supplementation is cheap as well as widely accessible, and excessive Ca excretion does not explicitly cause any environmental concerns. There have been very few studies that have attempted to separate the effects of the Ca: P ratio on the basis of digestibility, which takes into account endogenous losses of nutrients, rather than total concentrations in feed ingredients. Over the past 10 years, the Industry has formulated diets on the basis of total Ca: digestible P ratio (2:1). Formulating diets based on digestible Ca: digestible P ratio is essential to minimise P for a more effective minimisation of P excretion.Mathematical modelling can be seen as a useful tool to study P retention and excretion, incorporate factors such as Ca levels and phytase supplementation affecting these processes and in general, undertake many in-silico experiments which would not be possible in-vivo. Development of a new mathematical model accounting for the interactions between Ca and P should inform practices for overall reduction of the environmental impact caused by P and help to maximise nutrient utilisation benefiting swine production industry. The new model and DST will aim to accurately predict digestibility of Ca and its impact on animal excretion and growth. Simulation of the fate of digestible Ca in the model will lead to a more accurate prediction of reduction in P excretion and utilisation of P for growth. This objective has not been achieved so far by any prior model.