Modelling energy metabolism in the pig - critical evaluation of a simple reference model

Abstract

Although the reference model described in Chapter 7 is ideal for demonstrating the principles of protein and energy interaction in the growing pig, several of the assumptions are too simplistic for incorporation into simulation models that are to be used primarily to assist the management of commercial piggeries. In particular, the simple function relating voluntary feed intake to liveweight is inadequate. The predicted performance of a growing pig is extremely sensitive to the accurate assessment of feed intake, which is known to be influenced by the genotype of the animal, nutrient deficiencies such as minerals and amino acids, gut fill, stocking density, the number of animals in a pen, cold and hot climates, activity and disease. The energy required for maintenance of zero energy balance cannot be described adequately by a simple function relating it to metabolic liveweight because it is known to vary from at least 300 to 500 MJ/W0.75 d in response to energy intake, composition of the body, relative size of the gastrointestinal tract and liver, and the activity of the pig. The assumption that there is a constant genotype dependent minimum ratio of fat to protein deposition for energy intakes below that required for maximum protein deposition, also can cause major inaccuracies in predictions because this ratio is affected by energy intake, compensatory gain and cold climatic environments. In addition, the efficiency of use of available energy from the different nutrient cla…