Sow requirements for minerals is high during lactation, and the feed intake of certain sows in a group can be limited to meet their phosphorus (P) and calcium (Ca) requirements. When this occurs, phosphocalcic regulation may be activated to modify the quantity of minerals absorbed. Recent data on the apparent digestibility of P and Ca in lactating sows were used to establish the first mathematical model developed to predict the quantity of P and Ca absorbed as a function of the activation of phosphocalcic regulation. These data were generated from 24 primiparous sows fed one of four diets that provided 100 %, 75 %, or 50 % of the digestible P requirement, or that provided only 50 % of it but was supplemented with 500 FTU/kg phytase. Ingested mineral P, total Ca and exogenous phytase were used as predictors for the apparent total tract digestibility coefficient of P (ATTD-P) and Ca (ATTD-Ca). The model’s equations include a quadratic response of ingested mineral P and total Ca to represent phosphocalcic regulation. The model predicted ATTD-P and ATTD-Ca reliably (R² of 84 % and 68 %, respectively). This study forms part of an overall approach aiming to model phosphocalcic regulation in lactating sows, including dynamics of bone mineralisation.
