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Modelling analysis of phosphorus utilization and growth in the growing pig

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Title: Modelling analysis of phosphorus utilization and growth in the growing pig
Author: Schulin-Zeuthen, Mette
Department: Department of Animal and Poultry Science
Advisor: France, James
Abstract: The objective of the thesis is to evaluate applications of mathematical modelling in three diverse areas of research into the phosphorus (P) nutrition of growing pigs. Evaluation was carried out through non-linear curve fitting analyses of (i) growth (ii) P balance data, and through (iii) application of a 4 pool model of P metabolism for resolving isotope kinetic data. The mathematical methodology underlying the modelling in this thesis is based on principles describing flows between pools as functions of pool size (i.e., the rate:state formalism). This mechanistic approach uses differential equations and biologically meaningful descriptions of the inter-relationships involved. Meta-analysis of P balance data was conducted with 14 different balance trials using 350 pigs, all measuring dietary intake, and faecal and urinary excretion of P. In comparison with linear, Gompertz, and Richards functions, the monomolecular was best at describing the relationship between P retention and P intake. Estimates of endogenous secretion were (at zero P intake) 14 and 17 mg/(kg BW0.75·d) based on available and total P, respectively. Estimated requirement for maintenance was 15 mg available P/(kg BW0.75·d) and 37 mg total P/(kg BW0.75 ·d). In addition, the monomolecular was found to give best description of growth in live weight versus dietary intake of feed or P. It was demonstrated that efficiency of utilization for gain, which is the slope of the response curve, diminishes with increasing intake. In future analyses of growth in live weight versus age, it is recommended that the Schumacher as well as Gompertz and Richards equations should be considered. Finally, a 4 pool model for resolving both balance and isotope dilution data was applied. First, the model was compared with one of similar construction by analysing the effects of increasing dietary P intake on internal flows. Secondly, the model was used to analyse the effects of increasing levels of phytase enzyme on a bran-rich diet. The model was able to show different patterns of response, for instance in absorption from gut to blood, depending on the trial analysed.
Date: 2007
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