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)

The model incorporates, amongst its novel components, variable efficiency coefficients in the simulation of the responses of growing pigs to nutrient inputs, and thereby increases the accuracy and efficacy of control of feeding and nitrate excretion. The model determines (rather than is presented with) net energy and required amino acid level and balance. The estimation of protein turn-over as a function of rate of protein retention, protein mass and the maturity of the pig was found to be central to both the energy (ATP) and protein economy. Protein turn-over varied from around 0.14 to 0.08 of the protein mass depending upon the size of the pig. Efficiencies of energy yield from lipid, starch (and sugar), protein and (fibre-derived) volatile fatty acids were calculated to be 0.98, 0.86, 0.56 and 0.58 for ATP production and 0.90, 0.70, 0.50, and 0.44 for lipid retention, respectively. The maximum efficiency of use of ileal digestible amino acids was determined as around 0.85. The energy cost of protein synthesis was equivalent to 4.2 MJ metabolizable energy (ME) per kg, and the efficiency of use of ME for protein retention varied from 0.55 to 0.40 depending on the protein mass of the pig. The components of the model and the biochemical drivers are described in detail, and proof of principle of the main elements is presented. The model is different in its architecture to other published simulation models, and is considered to add to the present knowledge base in this discipline.