A pig model for feed evaluation.

Abstract

This chapter describes a dynamic, semi-mechanistic model of growing pigs. The purpose of the model is to predict growth rate and growth composition from given feed inputs and thereby serve as a basis for a new, nutrient-based feed evaluation system for slaughter pigs. The model consists of two submodels, one describing nutrient digestion and absorption, and one describing the metabolism of absorbed nutrients and their retention in the body pools of protein, lipid and ash. Required inputs to the model are: (i) characteristics of the food, such as dry matter content, chemical composition of dry matter, digestibilities and fermentabilities of individual chemical fractions; (ii) characteristics of the pig, such as age at the beginning of simulation, sex, and genetic capacities for protein and lipid retention; and (iii) environmental characteristics such as the ambient temperature. Model outputs are the simulated numeric values of all state and rate variables. From these numbers, the model calculates the predicted pig performance: food intake, retention of protein, lipid, ash and water, production of heat and methane, as well as faecal and urinary excretion of energy and matter. Some examples of simulated data obtained with the model are given in the chapter. The results of simulation were found to be realistic and biologically meaningful. In one test, the model was used to simulate the net energy value of 15 different diets. For each diet, the feed value simulated by the model was closer to the 'true' value determined experimentally than to the value estimated by the present Danish net energy system. It is concluded that a new feed evaluation system for growing pigs is needed. The possibilities and perspectives in the development of such a system based on a dynamic, whole animal simulation model like the one described are discussed.

Architecture of a harmonized model of the growing pig for the determination of dietary net energy and protein requirements and of excretions into the environment (IMS Pig)

“…Lower values for z will result in higher predicted rates of protein turn-over. The shape of the curve for protein turn-over rate as a function of pig mass, but not its locus, is similar to that suggested by Danfaer (2000);…”

Modelling of nutrient partitioning in growing pigs to predict their anatomical body composition. 1. Model description

“…New models have been introduced, each serving their own objective: some models have focused on nutrient digestion processes (Bastianelli et al 1996), on protein digestion in the small intestine (Rivest et al 2000) or on estimating amino acid requirements (Moughan, 1989). Others have aimed to model growth rate and its composition in terms of protein and lipid (Burlacu et al 1989;Pomar et al 1991;Danfaer, 2000;Birkett & de Lange, 2001b), or especially fatty acid composition of the body fat (Lizardo et al 2002), or improving understanding of different processes, such as protein turnover and ion pumping (Gill et al 1989b), or the process of growth (Lovatto & Sauvant, 2003). In addition, pig growth modelling efforts have been reviewed and various approaches have been discussed extensively (Black, 1995;Gerrits & Dijkstra, 2000;Halas & Babinszky, 2000;Birkett & de Lange, 2001a).…”

“…As acknowledged in more recently developed models, this approach ignored the effects of differences in the composition of the dietary energy (Danfaer, 2000;Birkett & de Lange, 2001a). In addition to models predicting chemical body composition, prediction of anatomical body composition is of great interest, relating chemical body composition to slaughter and meat quality.…”