Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2003
Publication Date: 6/1/2003
Citation: WILLIAMS, C.B., JENKINS, T.G. A DYNAMIC MODEL OF METABOLIZABLE ENERGY UTILIZATION IN GROWING AND MATURE CATTLE. II. METABOLIZABLE ENERGY UTILIZATION FOR GAIN. JOURNAL OF ANIMAL SCIENCE. 2003. v. 81. p. 1382-1389.
Interpretive Summary: Component models were developed to predict body tissue energy retention and daily gain in body weight. These models were based on a system that partitions food energy consumed by the animal into fractions that are: a) used for maintenance, b) retained in body tissue, c) lost as heat energy associated with the elevation of vital functions (support metabolism), and d) lost as heat energy directly associated with body tissue energy retention. Food energy used for production is the difference between consumption and utilization for maintenance and support metabolism. The first component model predicts the net efficiency of food energy utilization for gain as a function of composition of gain, and this net efficiency is used to calculate body tissue energy retention from the food energy available for production. Present energy systems use estimates of net efficiency that are constant within diet, and are not influenced by composition of gain. In contrast, this model uses separate partial efficiencies for protein and fat retention and the relative contributions of protein and fat to retained energy, to predict net efficiency. The second component model predicts daily gain as a function of body tissue energy retention and is represented by a system of ordinary differential equations that are numerically integrated on a daily basis. This model was developed by reformulating the equations in a published body composition model that uses daily gain to predict composition of gain, since recovered energy is a function of gain and composition of gain. These component models are part of a beef cattle production systems model, and it predicts daily gain and composition of gain, in response to changes in nutritional management. The systems model is used in decision support software to assist beef producers in evaluating the impact of strategic management decisions on future productivity.
Technical Abstract: Component models were developed to predict the net efficiency of ME utilization for gain in cattle and to predict daily gain using recovered energy as the input. These models were integrated into a single model to predict daily gain from ME available for gain. One component model predicts the net efficiency of ME utilization for gain using separate partial net efficiencies for ME retention as protein and fat, and the net efficiency of ME utilization for gain is predicted as a function of the ratio of the energy recovered in protein to the total energy recovered. Review of published literature and analysis of additional experimental data suggest that for ruminants, the partial net efficiencies of ME retention in protein and fat are about 0.2 and 0.75, respectively. The other component model predicts daily gain as a function of recovered energy and is represented by a system of ordinary differential equations that are numerically integrated on a daily basis. This model was developed by reformulating the equations in a published body composition model that uses daily gain to predict composition of gain, since recovered energy is a function of gain and composition of gain. The equations in the two component models are closely connected in the system, in that net efficiency is used to predict recovered energy from ME for gain, and in turn recovered energy is used to predict gain in empty BW. The predicted value for gain in empty BW is used to predict composition of the gain and energy retained in protein and fat, which is used to predict net efficiency. This net efficiency is then used with the input ME for gain value to update recovered energy, and the process is repeated until convergence for the net efficiency of ME utilization for gain is achieved.