ENERGY PARTITIONING AND MODELING IN ANIMAL NUTRITION

We first present a brief discussion of early and current models (feedi ng systems) used to estimate animal energy and protein requirements an d to predict performance based on feed composition and intake. We then touch on some limitations inherent in these systems. Next, we propose that dynamic (i.e. time-variant) models and mechanistic models (i.e, equations based on knowledge of physiological functions) are superior to earlier systems for both practical and research applications. Final ly, we describe a number of applied and research models of animal grow th and lactation to illustrate how biological concepts may be represen ted in equation form. Equations that represent current knowledge of un derlying functions can be used to improve predictions of animal requir ements and performance and to evaluate hypotheses about nutritional an d physiological mechanisms that influence animal performance.