A DYNAMIC MODEL OF METABOLIZABLE ENERGY UTILIZATION IN GROWING AND MATURE CATTLE. I. METABOLIZABLE ENERGY UTILIZATION FOR MAINTENANCE AND SUPPORT METABOLISM

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. I. METABOLIZABLE ENERGY UTILIZATION FOR MAINTENANCE AND SUPPORT METABOLISM. JOURNAL OF ANIMAL SCIENCE. 2003. v. 81. p. 1371-1381.

Interpretive Summary: Current models of food energy utilization partition food energy consumed by nonlactating, nonpregnant beef cattle into fractions that are: a) used for maintenance, b) retained in body tissue, and c) lost as heat energy resulting from the inefficiency of retaining food energy in body tissue. This latter fraction consists of costs associated with the elevation of vital functions in the productive animal, and costs that are directly associated with the body tissue energy retention, and is treated as a single dynamic pool. It is proposed that costs associated with the elevation of vital functions may be more accurately predicted from food intake, and costs that are directly involved in the body tissue energy retention may be more accurately predicted from composition of weight gain. A system is developed in which food energy consumed by the animal is partitioned 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. Models to predict heat production attributable to maintenance and support metabolism for 21 purebred and 15 crossbred cattle were developed on the basis of three concepts. The first concept is that animals fed fixed amounts of the same diet achieve weight equilibrium over an extended feeding period, and the ME consumed at weight equilibrium is the maintenance requirement. The second concept is that heat production associated with support metabolism can be modeled as a function of the level of feeding. The third concept is that previous levels of nutrition have an impact on current estimates of heat production, and that this impact can be modeled as a delayed response in heat production associated with support metabolism. The maintenance model differs from previous models in that it is based on simple proportionality of maintenance requirements to body weight. The model to predict heat production of support metabolism in productive animals is driven by level of feeding, which is calculated as a multiple of maintenance intake. These models are part of a beef cattle production systems model that 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: Models to predict heat production attributable to maintenance and support metabolism in growing and mature cattle were developed on the basis of three concepts. The first concept is that animals fed fixed amounts of the same diet achieve weight equilibrium over an extended feeding period, and the ME consumed at weight equilibrium is the maintenance requirement. The second concept is that a part of the heat production resulting from ME consumed above the maintenance requirement is associated with an elevation of vital functions or support metabolism, and this heat production can be modeled as a function of the level of feeding. The third concept is that previous levels of nutrition have an impact on current estimates of heat production, and that this impact can be modeled as a delayed response in heat production associated with support metabolism. Experimental data on feed consumption showed that maintenance requirements varied in simple proportion to BW, not only for different breeds of mature cattle at BW equilibrium, but also for calves and growing steers held at BW stasis. Experimental data in which different breeds of cattle achieved weight equilibrium when fed fixed amounts of a specific diet were used to estimate breed parameters associated with maintenance for 21 breeds of cattle and 15 biological types of crossbred cattle. Level of feeding was estimated as a multiple of the maintenance intake and used to model heat production associated with support metabolism. Other experimental data on growing cattle were used to estimate breed parameters for predicting heat production associated with support metabolism for 21 breeds of cattle and 15 biological types of crossbred cattle. A distributed lag function was used to model the delayed response in heat production associated with support metabolism with changes in plane of nutrition. The models were tested by simulating experimental data for three breeds of weaned steers finished on high energy diets. Results for the total heat production associated with maintenance and support metabolism expressed on a unit BW basis showed a similar response with stage of maturity when compared with other experimental data.