Integration of Energy Concepts by Modeling Techniques

¹ Department of Animal Science, University of California, Davis 95616

The TDN system uses only one feed energy value, although the partial efficiency of energy use for maintenance is greater than for gain. The California net energy system overcomes this limitation by separating energy requirements for maintenance from those for weight gain. Michigan researchers developed a set of adjustments for age, frame size, previous growth rate, breed type, environment, feed additives, and growth stimulants. In 1986, California workers proposed more general, dynamic models that include prediction of body composition based on cell number and size mechanisms of growth to predict net protein synthesis. However, accuracy of fat gain prediction is variable; therefore, integrated models of growth with digestion and metabolism have been developed in England and in California. The later model has equations for two pools of DNA and protein and one fat pool; partial efficiencies of nutrients for maintenance and production may be evaluated. With each new model, prediction accuracy was improved by addition of new terms to conceptually validated models that were already accepted and in use. These terms were added using either empirical adjustment factors or mechanistic concepts and representations of biological functions at lower levels of aggregation.

Key Words: growth models • beef cattle • energetics

Submitted on June 8, 1992
Accepted on October 26, 1992