title: Meta-analysis of phosphorus balance data from growing pigs.
abstract: 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) x 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) x d and 37 mg of total P/kg of BW(0.75) x 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.
authors.affiliation: Centre for Nutrition Modelling, Department of Animal and Poultry Science, University of Guelph, Ontario, N1G 2W1, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Schulin-Zeuthen
authors.forename: E
authors.initials: E
authors.lastname: Kebreab
authors.forename: W J J
authors.initials: WJ
authors.lastname: Gerrits
authors.forename: S
authors.initials: S
authors.lastname: Lopez
authors.forename: M Z
authors.initials: MZ
authors.lastname: Fan
authors.forename: R S
authors.initials: RS
authors.lastname: Dias
authors.forename: J
authors.initials: J
authors.lastname: France
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D008954:Models, Biological; D016226:Phosphorus, Dietary / Q000378:metabolism* / Q000493:pharmacokinetics; D013552:Swine / Q000254:growth & development / Q000378:metabolism*
chemical_list: D016226:Phosphorus, Dietary