Meta-analysis of phosphorus balance data from growing pigs

¹ Centre for Nutrition Modelling, Department of Animal and Poultry Science, University of Guelph, ON, N1G 2W1, Canada
² Animal Nutrition Group, Wageningen Institute of Animal Sciences, Wageningen University, 6709 PG Wageningen, The Netherlands
³ Departamento de Produccion Animal, Universidad de León, 24071 Leon, Spain
⁴ Animal and Poultry Science, University of Guelph, Guelph, Canada

^* To whom correspondence should be addressed. E-mail: ekebreab{at}uoguelph.ca.

	Abstract

Many studies have highlighted concerns over current methods of determining endogenous phosphorus (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: straight line, a diminishing returns function (monomolecular), a sigmoidal function with a fixed point of inflection (Gompertz), and a sigmoidal function with a flexible point of inflection (Richards). The nonlinear functions were specifically re-parameterized to assign biological meaning to 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 nonlinearity in the data and the monomolecular provided the best fit of the data. The Richards function did not fit the data well and appeared over-parameterized. Estimates of endogenous P excretion of 14 and 17 mg/(kg BW^0.75·d) based on available and total P analysis, respectively, were predicted by the monomolecular, which were within the range reported in the literature. Maintenance requirement values of 15 mg available P/(kg BW^0.75·d) and 37 mg total P/(kg BW^0.75·d) were obtained, based on the monomolecular function. 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 fitted the data best, more observations at high P intakes/kg 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 P excretion, mathematical models, P balance, P maintenance requirement, pigs

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