A New Method for Estimating Energetic Efficiencies

Abstract

A new method is proposed for estimation of energetic efficiency for fat and lean tissue gains in growing animals. The method involves the partition of metabolizable energy available for growth (MEA) into fat and lean tissue synthesis. The Michaelis-Menten type equation is used to describe the effect of level of MEA on the proportion of MEA being used for fat or lean synthesis. A system of two simultaneous non-linear equations was used to calculate fat gain (FG) and lean gain (LG) as a function of MEA. The partial efficiencies for fat gain (Ef) and lean gain (E1) as well as the Michaelis-Menten constant (K) were estimated from data obtained from energy balance trials involving two lines of mice by using a non-linear least squares procedure. The results of this study showed that mice, which have been selected for rapid postweaning weight gain, utilized MEA more efficiently for fat and lean tissue syntheses than mice from control groups. At all intake levels, mice from selected lines utilized more of the MEA for fat synthesis than control mice. This new method overcomes some of the problems involved when a multiple regression technique is used for the estimation of partial efficiencies. Upon extension and improvement, the method can be used not only for the estimation of true partial efficiencies, but also for identification of factors that influence how MEA is partitioned for fat and lean energy synthesis.