Modelling the mechanisms of pig growth

The objectives and constraints of pig production have changed. It is now necessary to consider not only feed efficiency but also the quality of products and the fluxes of excreta. To do this, the various animal response curves to dietary changes and to the environment need to be predicted simultaneously. These objectives can be more effectively achieved by using mechanistic rather than empirical models, because the latter allow a fuller integration of present-day knowledge concerning growth mechanisms. The simplest approach developed to deal with this subject was to consider only the kinetics of the pools of body proteins and fat without distinction between the various organs and tissues. Such models can show satisfactory responses by simply evaluating the major nitrogen and energy fluxes through the organism. These models sometimes integrate other factors causing variations such as the sex of the animals, characterization of genotypes, and environmental parameters. However, a more mechanistic approach to growth requires a less aggregative description of the metabolism of absorbed nutrients than the simple partitioning rules defined at a whole animal level used in former models. The time steps within a model need to be shorter than a day. It is necessary to model the feeding pattern and the supply of nutrients to the organism during shorter time steps to enable prediction of feed intake, digestion and nutrient absorption. (C) 1997 Elsevier Science B.V.