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Meta-analysis of phosphorus balance data from growing pigs

M. Schulin-Zeuthen^*, E. Kebreab^*,1,2, W. J. J. Gerrits, S. Lopez, M. Z. Fan^*, R. S. Dias^* and J. France^*

^* Centre for Nutrition Modelling, Department of Animal and Poultry Science, University of Guelph, Ontario, N1G 2W1, Canada; and Animal Nutrition Group, Wageningen Institute of Animal Sciences, Wageningen University, 6709 PG, the Netherlands; and and Departamento de Produccion Animal, Universidad de León, 24071, Spain

¹ Corresponding author: Ermias_Kebreab{at}umanitoba.ca

Many studies have highlighted concerns over current methods of determining endogenous P losses and P requirements in growing pigs. Therefore, a database containing observations on 350 pigs was assembled from various studies. Four functions for analyzing P balance data were considered: 1) a straight line, 2) a diminishing returns function (monomolecular), 3) a sigmoidal function with a fixed point of inflection (Gompertz), and 4) a sigmoidal function with a flexible point of inflection (Richards). The nonlinear functions were specifically reparameterized to assign biological meaning to the parameters. Meta-analysis of the data was conducted to estimate endogenous P excretion, maintenance requirement, and efficiency of utilization. Phosphorus retention was regressed against either available P intake or total P intake [all variables scaled by metabolic BW (BW^0.75)]. There was evidence of non-linearity in the data, and the monomolecular function provided the best fit to the data. The Richards equation did not fit the data well and appeared overparameterized. Estimates of endogenous P excretion of 14 and 17 mg/kg of BW^0.75 · d based on available and total P analysis, respectively, were predicted by the monomolecular equation, which were within the range reported in the literature. Maintenance requirement values of 15 mg of available P/kg of BW^0.75 · d and 37 mg of total P/kg of BW^0.75· d were obtained, based on the monomolecular equation. Average efficiencies of conversion of dietary P to retained P were 65 and 36% for available and total P, respectively, with greater efficiency values calculated for low P intakes. Although the monomolecular equation fitted the data best, more observations at high P intakes/kg of BW^0.75 are required to determine conclusively whether P retention scaled by metabolic BW is linearly related to available or total P intake.

Key Words: endogenous phosphorus excretion • mathematical model • phosphorus balance • phosphorus maintenance requirement • pig