Mechanisms by which Ã-adrenergic agonists alter growth and body composition in ruminants

A.P. Moloney; D.H. Beermann

Mechanisms by which Ã-adrenergic agonists alter growth and body composition in ruminants

äºResidues of Veterinary Drugs and Mycotoxins in Animal Products

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A.P. Moloney

A.P. Moloney Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland

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D.H. Beermann

D.H. Beermann Department of Animal Science, Cornell University, Ithaca, New York, U.S.A.

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Page Range:: 124â136

DOI:: https://doi.org/10.1163/9789004684171_019

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Summary

There is a sustained consumer demand for low(er) fat food products. In response to this demand, a variety of technologies have been developed to decrease fat accretion in meat-producing livestock. Among the most attractive is administration of orally active Ã-adrenergic agonists. These compounds which are analogues of the naturally occurring catecholamines, improve the efficiency of production of carcass lean meat, especially in ruminants.

While there is some variation in apparent efficacy between the different compounds, dose rates in the range of 2-4 ppm in the diet are indicated for cattle with the repartitioning effects being more consistent than the effects on body weight gain. Ractopamine is an exception with a maximum response at 15 ppm and 20 ppm for growth and efficiency, respectively. There is evidence that administration of Ã-agonists for the finishing period is more effective than feeding for longer periods. Similar effects are seen in sheep when Ã-agonists are fed at 2-4 ppm in the diet for 6-8 weeks. In general, Ã-agonists are effective in reducing carcass fatness in any breed or sex, but decrease meat tenderness, with ruminants particularly affected. The magnitude of this effect is likely related to the dose of agonist used and reflects a decrease in proteolytic activity both in the live animal and post-mortem. The reduction in body fat results from a combination of increased lipolysis, decreased lipogenesis and possibly decreased preadipocyte recruitment. The increase in skeletal muscle results from a combination of an increase in protein biosynthesis and a decrease in protein degradation. It is unlikely that metabolic hormones are directly involved in the action of Ã-agonists. Increased blood flow to peripheral tissues may accommodate the greater capacity for amino acid uptake and protein accretion due to Ã-agonist treatment. Use of the lowest dose that causes a re-partitioning effect, observation of a withdrawal period prior to slaughter, possible modification of carcass processing procedures and the development of compounds with greater specificity then those evaluated to date should all help to decrease any negative effects of Ã-agonist treatment on meat quality. However, even if all criteria of efficacy and safety demanded by European regulatory bodies are satisfied, the eventual use of Ã-agonists in meat production is likely to be determined largely by political considerations.

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Residues of Veterinary Drugs and Mycotoxins in Animal Products

New Methods for Risk Assessment and Quality Control

ISBN:: 9789004684171

åºçç¤¾:: Wageningen Academic

å°å·åºçæ¥æ:: 01 Jan 1996

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Mechanisms by which Ã-adrenergic agonists alter growth and body composition in ruminants

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