Modelling the phosphorous intake, digestion, utilisation and excretion in growing and finishing pigs

Abstract

The overall aim was to develop a model of Phosphorous (P) intake, digestion, utilisation and excretion in growing/finishing pigs, and use it to investigate the consequences of different P management strategies. Initially, a dynamic, deterministic model was developed (Chapter 2). It was able to predict the digestible (digP) requirements of pigs of different genotypes and stages of growth, as well as the consequences of different dietary contents of P, Calcium (Ca) and exogenous phytase. The model was also able to predict the excreted amounts of soluble and insoluble P. Subsequently (Chapter 3) the model was evaluated against independent data and a sensitivity analysis of its predictions to model parameters was undertaken. Model outputs were most sensitive to the values of the efficiency of digP utilization and the non-phytate P absorption coefficient from small intestine. The model predicted satisfactorily the quantitative pig responses, in terms of P digested, retained and excreted, to dietary variations. The model performed well with ‘conventional’, European feed ingredients and poorly with ‘less conventional’ ones, such as DDGS and canola meal. In Chapter 4 the model was converted into stochastic, by introducing variation between pig digP requirements and the consequences of two strategies were investigated (phase feeding and sorting). The former was more effective in reducing P excretion than the latter. Finally the model was extended to include uncertainty in feed composition (arising from variability in ingredient nutrient content and mixing efficiency) to investigate how this would affect the outputs of the model. Due to the assumptions made, uncertainty about feed ingredient composition contributed more to performance variation than uncertainty regarding mixing efficiency. When uncertainty about both feed composition and pig characteristics was considered, it was uncertainty about feed composition rather than pig genetic characteristics that proved to have the dominant influence on variability in pig performance.