A DYNAMIC MODEL OF METABOLIZABLE ENERGY UTILIZATION IN GROWING AND MATURE CATTLE. III. MODEL EVALUATION

Authors: Williams, Charles; Jenkins, Thomas

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. III. MODEL EVALUATION. JOURNAL OF ANIMAL SCIENCE. 2003. v. 81. p. 1390-1398.

Interpretive Summary: Component models of heat production identified in a proposed system of partitioning food energy consumed, and a dynamic systems model that predicts daily gain in body weight in cattle resulting from a known consumption of food energy were evaluated. Evaluation results showed that the component models provided accurate predictions of observed responses for the represented sub-systems, and evaluations of the integrated system showed that it provided an accurate representation of the real system. The impact of previous and present level of feeding on requirements for metabolizable energy is modeled as a distributed lag function of support metabolism, and this increased the prediction accuracy of the model under varying levels of nutritional management. The integrated system model is used as a complete package in decision support software; however, the maintenance, support metabolism, and efficiency of metabolizable utilization for gain components may be used with a different set of assumptions to develop other system models.

Technical Abstract: Component models of heat production identified in a proposed system of partitioning ME intake, and a dynamic systems model that predicts gain in empty BW in cattle resulting from a known intake of ME were evaluated. Evaluations were done in four main areas: 1) net efficiency of ME utilization for gain, 2) relationship between recovered energy and ME intake, 3) predicting gain in empty BW from recovered energy, and 4) predicting gain in empty BW from ME intake. An analysis of published data showed that the net partial efficiencies of ME utilization for protein and fat gain were approximately 0.2 and 0.75 respectively, and that the net efficiency of ME utilization for gain can be estimated using these net partial efficiencies and the fraction of recovered energy that is contained in protein. Analyses of published sheep and cattle experimental data showed a significant linear relationship between recovered energy and ME intake, with no evidence for a nonlinear relationship. Growth and body composition of Hereford × Angus steers simulated from weaning to slaughter showed that over the finishing period 20.8% of ME intake was recovered in gain. These results were similar to observed data and comparable to feedlot data of 26.5% for a shorter finishing period with a higher quality diet. The component model to predict gain in empty BW from recovered energy was evaluated with growth and body composition data of five steer genotypes on two levels of nutrition. Linear regression of observed on predicted values for EBW resulted in an intercept and slope that were not significantly different from 0 and 1, respectively. Evaluations of the dynamic systems model to predict gain in empty BW using ME intake as the input showed a close agreement between predicted and observed final empty BW for steers that were finished on high energy diets, and the model accurately predicted growth patterns for Angus, Charolais, and Simmental reproducing females from 10 mo to 7 yr of age.