PSIV-15 Development of a modelling framework to account for P kinetics in growing and finishing pigs

Abstract Key underlying assumptions of current pig growth models, developed in the context of nutritionally balanced feeds, may be invalid for pigs given inadequate dietary phosphorous (P). To account for pig performance on feeds of different P content, a dynamic, mechanistic growth model was developed where ingested P is allocated to either soft tissue or skeletal tissue. The following issues needed to be addressed: 1) potential impact of different dietary P concentrations on feed intake; 2) estimation of the whole-body protein (Pr):P relationship; 3) allocation of ingested P into different body tissues. Statistical analyses of the published literature data, utilising meta-regression indicated the following answers: 1) there was no compensatory feed consumption in pigs fed P-deficient diets (p > 0.05); 2) the whole-body Pr:P relationship was feed-dependent, i.e., body P was directly proportional to body Pr in pigs fed P-adequate diets but lower in pigs fed P-deficient diets; 3) P retention in the soft tissue was prioritised over P deposition in bone when the dietary P was low (p < 0.001). A growth model incorporating mechanisms based on the above data analyses suggests that pigs given P-limiting feeds attempt to maintain the same level of lean tissue retention attained with a P-balanced diet, but at the expense of reduced skeletal deposition. Specifically, bone P growth was reduced in relation to a balanced-diet for moderately-P-deficient diets, and static for severely-P-deficient diets. The overall average daily gain remained largely unaffected for moderately-P-deficient pigs. The present in-silico framework of P kinetics could be utilised to study the consequences of different P feeding strategies on animal growth and body composition, and to verify whether further reduction in dietary P requirements could be achieved with no loss in animal performance.