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Development of a dynamic, mechanistic model of lamb metabolism and growth

Published online by Cambridge University Press:  02 September 2010

R. D. Sainz  and
J. E. Wolff
R. D. Sainz
Affiliation:
Growth Physiology Group, Ruakura Agriculture Centre, Ministry of Agriculture and Fisheries, Hamilton, New Zealand
J. E. Wolff
Affiliation:
Growth Physiology Group, Ruakura Agriculture Centre, Ministry of Agriculture and Fisheries, Hamilton, New Zealand
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Abstract

A dynamic, mechanistic model of lamb metabolism and growth was developed for the purpose of evaluating hypotheses regarding the mechanisms of action of growth promotants. The model relates tissue growth to DNA accretion and protein turn-over. State variables include circulating amino acids, glucose, lipids and acetate; four protein pools (carcass, viscera, other tissues and wool) and storage triacylglycerol are also included. Equations are mainly of the Michaelis-Menten form, allowing for nutrient utilization patterns to be determined by relative tissue affinities for substrates (ko.5), enzymatic capacities (Vmax) and substrate concentrations ([S]). Protein degradation rates are defined as first-order with respect to protein. The model adequately simulated growth from 20 to 40 kg empty body weight. Simulated changes in nutrient input yielded reasonable energy balance response patterns, although theoretical growth efficiencies were greater than those observed in practice. Variations in volatile fatty acid absorption patterns were accommodated well, with predicted nitrogen retention closely approximating experimental observations. The model also responded appropriately to changes in dietary protein level, with body fat varying inversely with amino acid absorption. In summary, the model was found to perform adequately for the purpose of examining mechanisms responsible for alteration of growth and body composition.

Keywords

growthlambsmathematical modelsmetabolism
Type
Research Article
Information
Animal Production , Volume 51 , Issue 3 , December 1990 , pp. 535 - 549
Copyright
Copyright © British Society of Animal Science 1990

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