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Development of a Dynamic Model of Beef Cattle Growth and Composition

University of California, Davis 95616

Abstract

A dynamic model of postweaning growth and composition of the beef steer has been developed. In a previous rat model, fundamental biological concepts describing growth of individual mammalian organs and tissues were aggregated to the whole animal level and represented by differential equations for whole body DNA and protein accretion. Frame size, or mature body weight, affects nucleic acid content that drives protein synthesis. Equations reflecting characterjstic rates of lean body mass accretion were fitted to an average frame size steer for initial parameter estimation. Sensitivity analysis revealed that the model was identifiable for cattle. Effects of nutrition on rates of DNA and protein synthesis were determined using a latge set of data containing records of body weight, frame size, composition and energy intake. Net synthesis of body fat is calculated as net energy available after accounting for maintenance and protein accretion. Beginning body weight and composition, and mature body weight are required as initial inputs; feed intake and net energy concentrations for maintenance and gain are input daily and body weight and composition are simulated. The model predicted empty body weight and fat content with a Standard deviation of 14 and 10 kg, respectively. No systematic errors were found with composition, frame size or energy intake.

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