Preliminary model to predict P-requirement of growing pigs

Phosphorus is an essential nutrient and, as phosphate, is involved in most of the metabolic activities of the body as well as in bone formation. There are evidences that long term P deficiency reduces the growth rate of animals, however, oversupply results in high rate of excretion that is critical from environmental point of view. Modelling P metabolism gives a tool for improving our understanding on the main factors affecting the P requirement. Towards sustainable animal production that information is necessary to be used for precise diet formulation. The aim of the work was to develop a mathematical model predicting the dynamics of P partitioning and retention in growing and fattening pigs over time. The model is a comprehensive description of the underlying mechanisms of digestible P and Ca utilization. Input parameters are related to diet such as dry matter, dietary Ca and P content of the feed, as well as Ca and P digestibility, and to the animal such as daily feed intake, protein and fat deposition rate. The model presents the distribution of true digestible P and Ca within the body. Absorbed P and Ca are used for maintenance purposes, soft tissues (muscle and backfat), and bone tissue development. Surplus P and Ca is excreted via urine. Retention of P in the body is the sum of P retention in soft tissues and skeleton. It is presumed that soft tissues have a priority in utilizing the absorbed P. Thus upon insufficient P supply the bone ash retention decreases to ensure P for the soft tissue development. However, there is a limit for rate of demineralization and under the threshold level, the absorbed P has priority to be retained in bone over soft tissues. The bone formation depends on P bioavailability and Ca supply, and limited by potential bone P retention. It is assumed that the absorbed P can be used for maintenance purposes with 100%, while for retention with 94% efficiency. The model is able to predict P-retention, urinary P excretion and digestible P requirement of swine at different body weight and upon different body composition. The results show that the P requirement depends on growth rate and particularly on protein deposition of the pigs. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 633531.