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Evaluation of hypotheses regarding mechanisms of action of growth promotants and repartitioning agents using a simulation 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

Responses of lambs to cimaterol (CIM), diethylstylbestrol (DES) and ovine growth hormone (GH) were examined using a mechanistic model of growing lamb metabolism. All three compounds increase growth of lean tissue (protein) and decrease fat gain, although the magnitudes of these responses vary. Our working hypothesis was that observed changes in nutrient partition between lean and fat gain were caused by alteration of rate constants for turn-over of muscle protein and fat. Individual experiments were simulated whilst varying values of the protein degradation constant (Kprolein) and Vmax for lipolysis (Kfat). Optimal parameter values were found by minimizing residual errors, calculated as the deviations of model predictions from experimental values for carcass protein and fat. Fitted values of Kfat and Kprotein (expressed as proportions of controls) for each simulation were: CIM (grazing), 1·20 (s.d. 0·05) and 0·86 (s.d. 0·025); CIM (pellet-fed), 1·11 (s.d. 0·115) and 0·87 (s.d. 0·032); DES, 1·33 (s.d. 0·111) and 0·94 (s.d. 0·024); GH, 1·77 (s.d. 0·139) and 0·97 (s.d. 0·025) respectively. These results demonstrate that different mechanisms may be responsible for the changes in carcass composition due to 3-adrenergic agonists, anabolic steroids and growth hormone. CIM probably exerts its effects via changes in protein and fat metabolism, whereas DES and GH appear to act mainly through changes in adipose tissue, with little or no effect on the rate constant for protein turn-over. Carcass composition is less sensitive to manipulation of adipose tissue metabolism than to changes in muscle protein metabolism.

Keywords

growth promoterslambsmathematical modelsmetabolism
Type
Research Article
Information
Animal Production , Volume 51 , Issue 3 , December 1990 , pp. 551 - 558
Copyright
Copyright © British Society of Animal Science 1990

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