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

该项目涉及BBSRC的战略优先事项：与畜牧业有关的农业和粮食安全，特别是应用于动物饲料的生物技术的优先事项。本研究旨在探讨外源植酸酶与猪饲料中磷(P)和钙(Ca)含量之间的相互作用，以期更好地利用饲料。这将在一个现有的模拟模型的背景下完成，该模型支持一个决策支持工具(DST)，以减少英国生长和肥育猪的磷排泄和改善生长。众所周知，钙和磷都具有重要的骨骼和生理功能。同时，磷是猪日粮中第三昂贵的成分，因为植物日粮磷的消化率较低，因此需要补充昂贵的无机磷补充剂。从环境的角度来看，磷的供应是有限的，不可再生，饲料转化效率低，导致粪便中水溶性磷的高排泄，以富营养化的形式造成水污染。业界，例如AHDB猪肉，认识到在确保猪的生产性能和健康保持的同时减少磷排泄的重要性，并参与了实现这些目标的研究。大部分植物基磷和猪饲料中的大多数磷都结合到植酸分子上。这种形式的磷不能被非反胃动物消化，因为它们不能产生植酸脱磷所需的足够水平的内源性植酸酶。一种日益流行的提高植物基磷生物利用率的方法是通过补充外源植酸酶。外源植酸酶将植酸分子水解，释放出无机磷，然后被动物吸收。据估计，添加外源植酸酶可以减少30-60%的磷排泄，这将允许较低水平的磷在猪日粮中的补充。然而，为了充分了解手头的问题，必须同时研究磷的消化、吸收和排泄与钙，因为这两种主要的宏观矿物质在猪的消化道中相互依赖和相互作用。从历史上看，钙没有引起像磷那样多的学术兴趣，钙被认为是导致植酸盐-磷生物利用度的最被低估的因素。这主要是因为无机钙补充剂既便宜又容易获得，而且过量的钙排泄不会明显造成任何环境问题。很少有研究试图根据消化率来区分钙磷比的影响，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，该行业以总钙：可消化磷的比例(2：1)为基础制定了饲料。根据可消化钙和可消化磷的比例设计饲料，对于最大限度地减少磷的排泄是至关重要的。数学模型可以被视为研究磷滞留和排泄的有用工具，纳入了影响这些过程的因素，如钙水平和植酸酶补充，一般情况下，进行许多在体内不可能的电子实验。开发一种新的数学模型来解释钙和磷之间的相互作用，应该有助于全面减少磷对环境的影响，并有助于最大限度地利用养分，造福于养猪业。新的模型和DST将旨在准确预测钙的消化率及其对动物排泄和生长的影响。对模型中可消化钙的去向进行模拟，将导致更准确地预测磷排泄的减少和磷的生长利用。到目前为止，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.