Animal Growth Modelling 
Stephen Birkett

Piano Design
Physical Systems
Animal Growth Modelling
Environmental Systems

Linear Algebra
Numerical Methods
Computational Mathematics
Musical Instruments

Marcia Hadjimarkos

The International Pig Growth Modelling Group (IPGM) is a collaborative research effort between the University of Guelph, Massey University (New Zealand) and Wageningen Agricultural University (Netherlands). This work was sponsored by the industrial partner Agribrands Purina Canada (Cargill International) during the period 1994 to 2001. The main objective of the project was to develop the biological and nutritional principles to support a practical pig growth model based on an explicit representation of nutrient flows. Process network submodels are incorporated to represent the bioenergetics of nutrient metabolism, protein utilization, and a means to characterize variation between animal genotypes. The model has been extensively tested with both experimental data and in a practical production context. Simulation software based on the new growth model was constructed, including a flexible user interface and a simple means to calibrate model parameters and inputs when applying it to a specific pig production unit. This new pig growth model is at the forefront of current approaches to modelling animal nutrition.

Related research activity continuing from this modelling project is developing an environmental assessment system for pig production. The impact of commercial pork production operations may be assessed in terms of excretion of nitrogen, phosphorus and potassium with manure in relation to nutritional strategy and animal management.

The concepts of the nutrient flow pig growth model are also being adapted to the development of a model for salmonid fish growth. This model will be applied to the problem of improving the environmental impact of aquaculture operations at the source through improved nutritional management. This collaborative project is sponsored in part by a grant from AquaNet, the Canadian Network of Centres of Excellence in aquaculture.

Articles presenting the nutrient based growth model are available:

SH birkett & CFM de lange (2001a). Limitations of conventional models and a conceptual framework for a nutrient flow representation of energy utilization by animals. British J. Nutrition 86: 647-659.
  Abstract. Conventional models of energy utilization by animals, based on partitioning metabolizable energy (ME) intake or net energy (NE), are reviewed. The limitations of these methods are discussed, including various experimental, analytical and conceptual problems. Variation in the marginal efficiency of utilizing energy can be attributed to various factors: diet nutrient composition; animal effects on diet ME content; diet and animal effects on ME for maintenance (MEm); experimental methodology; and important statistical issues. ME partitioning can account for some of the variation due to animal factors, but not that related to nutrient source. In addition to many of the problems associated with ME, problems with NE pertain to: estimation of NE for maintenance (NEm); experimental and analytical methodology; and an inability to reflect variation in the metabolic use of NE. A conceptual framework is described for a new model of energy utilization by animals, based on representing explicit flows of the main nutrients and the important biochemical and biological transformations associated with their utilization. Differences in energetic efficiency from either dietary or animal factors can be predicted with this model.
SH birkett & CFM de lange (2001b). A computational framework for a nutrient flow representation of energy utilization by growing monogastric animals. British J. Nutrition 86: 660-674.
  Abstract. A computational framework to represent nutrient utilization for body protein and lipid accretion by growing monogastric animals is presented. Nutrient and metabolite flows, and the biochemical and biological processes which transform these, are explicitly represented. A minimal set of calibration parameters is determined to provide five degrees of freedom in the adjustment of the marginal input-output response of this nutritional process model for a particular (monogastric) animal species. These parameters reflect the energy requirements to support the main biological processes: nutrient intake, faecal and urinary excretion, and production in terms of protein and lipid accretion. Complete computational details are developed and presented for these five nutritional processes, as well as a representation of the main biochemical transformations in the metabolic processing of nutrient intake. Absolute model response is determined as the residual nutrient requirements for basal processes. This model can be used to improve the accuracy of predicting the energetic efficiency of utilizing nutrient intake, as this is affected by independent diet and metabolic effects. Model outputs may be used to generate mechanistically predicted values for the net energy of a diet at particular defined metabolic states.
SH birkett & CFM de lange (2001c). Calibration of a nutrient flow model of energy utilization by growing pigs. British J. Nutrition 86: 675-689.
  Abstract. A computational framework to represent energy utilization for body protein and lipid accretion by growing pigs is presented. Nutrient and metabolite flows, and the biochemical and biological processes which transform these, are explicitly represented in this nutritional process model. A calibration procedure to adjust the marginal input-output response is described, and applied, using reported experimental results, to determine a complete set of parameters for representing energy utilization by growing pigs. A reasonable value for minimum basal energy requirements is also determined. Although model inputs and outputs need not at any time be converted to equivalent energy flows, to facilitate comparison of model response with that of conventional energy-based models, a simple means to estimate energy flows from model-predicted nutrient flows is described. The well-known hierarchy of marginal (biological) energetic efficiencies with which pigs use different classes of nutrients is predicted by the model, based only on simple biological and biochemical principles. The significance of independent diet and metabolic effects on both energetic efficiency and maintenance requirements is examined using model predictions from simulated experiments.

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©2004 Stephen Birkett