Modelling phosphorus intake, digestion, retention and excretion in growing and finishing pigs: model description.
Modelling phosphorus intake, digestion, retention and excretion in growing and finishing pigs: model description.
复制标题
模拟生长猪和肥育猪的磷摄入、消化、保留和排泄：模型描述。
作者：
V. Symeou;I. Leinonen;I. Kyriazakis
低磷消化率与集约化养猪相结合，会增加磷的扩散污染和环境负荷。本文的目的是建立一个确定性的，动态模型，能够代表P消化，滞留和最终排泄在生长和肥育猪的不同基因型，提供了访问不同的组成。该模型代表了猪内源性植酸酶活性的有限能力，以脱磷酸化植酸作为线性函数的膳食钙（Ca）。外源微生物植酸酶在胃内对植酸的脱磷酸作用符合一级动力学关系。从小肠腔到血流中的非植酸盐P的吸收被设定为0.8，并且来自大肠的去磷酸化植酸盐被认为是不可消化的。利用消化的P的净效率被设定为0.94，并假设是独立的BW，并在基因型和性别恒定。维持和生长所需的磷是机体蛋白质量的简单函数，因此也是动物基因型的函数。未消化的P被认为是以可溶性和不溶性形式排泄在粪便中。如果可消化的P超过了P的需求，则过量的可消化的P通过尿流排泄;因此，该模型代表了两种形式的P排泄（可溶性和不溶性）到环境中。使用英国工业标准饮食，模型行为进行了研究，其预测的P消化率，保留和排泄下的不同水平的微生物植酸酶和膳食钙，以及不同的非植酸磷：植酸盐的比例在饮食中，从而涵盖了广阔的空间潜在的饮食组合物。模型预测与我们的理解是一致的P消化，代谢和排泄。与该模型的基本假设相关的不确定因素已被确定。它们对模型预测的影响，以及模型评估在一个配套文件进行评估。
Low phosphorus (P) digestibility combined with intensive pig production can increase P diffuse pollution and environmental load. The aim of this paper was to develop a deterministic, dynamic model able to represent P digestion, retention and ultimately excretion in growing and finishing pigs of different genotypes, offered access to diets of different composition. The model represented the limited ability of pig endogenous phytase activity to dephosphorylate phytate as a linear function of dietary calcium (Ca). Phytate dephosphorylation in the stomach by exogenous microbial phytase enzymes was expressed by a first order kinetics relationship. The absorption of non-phytate P from the lumen of the small intestine into the blood stream was set at 0.8 and the dephosphorylated phytate from the large intestine was assumed to be indigestible. The net efficiency of using digested P was set at 0.94 and assumed to be independent of BW, and constant across genotype and sex. P requirements for both maintenance and growth were made simple functions of body protein mass, and hence functions of animal genotype. Undigested P was assumed to be excreted in the feaces in both soluble and insoluble forms. If digestible P exceeded the requirements for P then the excess digestible P was excreted through the urinary flow; thus the model represented both forms of P excretion (soluble and insoluble) into the environment. Using a UK industry standard diet, model behaviour was investigated for its predictions of P digestibility, retention and excretion under different levels of inclusion of microbial phytase and dietary Ca, and different non-phytate P : phytate ratios in the diet, thus covering a broad space of potential diet compositions. Model predictions were consistent with our understanding of P digestion, metabolism and excretion. Uncertainties associated with the underlying assumptions of the model were identified. Their consequences on model predictions, as well as the model evaluation are assessed in a companion paper.