THE MERCK VETERINARY MANUAL
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Overview of Growth Promotants and Production Enhancers

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Achieving increased efficiency of feed conversion into edible human food products of high quality, without posing any significant risk to the consumer, is an important goal of livestock producers worldwide. The physiologic mechanisms involved in converting feed into muscle, fat, and bone by animals are increasingly being elucidated. Recently, consumer concerns about additives for food production have focused on animal safety, organoleptic quality, and the potential human health hazards of the food we eat.

A number of approaches may be taken to improve conversion of animal feed into meat; two of the more practical approaches are hormonal treatments and antimicrobial feed additives. The hormonal approach includes administration of anabolic steroid hormones, use of growth hormone (GH) or insulin-like growth factor (IGF-1) to augment endogenous GH levels, and use of β-adrenergic agonists (βAAs) to preferentially increase nutrient partitioning to muscle (see Natural Steroid Hormones for Consideration as Growth PromotersTables). The antimicrobial feed additives approach includes feeding of antibiotics to decrease populations of pathologic bacteria in host GI tracts, use of compounds to manipulate ruminal fermentation by changing the ruminal microflora population in healthy animals, and use of probiotics to promote beneficial microflora in the GI tract.

The use of hormonal treatments and antimicrobial feed additives in production animals is currently under debate in many areas and is banned in some because of concerns surrounding their possible effects on people.

The EU has banned beef produced using growth-promotant implants since 1981. Despite subsequent findings by the European Economic Community's own panel of scientific experts, referred to as the "Lamming Committee," by the World Trade Organization, and by the international Codex Alimentarius Commission indicating that appropriate use of approved growth-promoting hormones poses no human health risk to consumers, the EU has continued its ban.

More recently, use of βAAs for growth promotion in swine and beef production has come under scrutiny in the international meat trade community. Some countries, including the EU, Russia, and China, have placed a total ban on beef and pork from nations that allow the use of βAAs, whereas other countries have adopted the maximum residue limits (MRLs) for the compounds as established by the Codex Alimentarius Commission. The FDA applies a higher MRL in the USA than the Codex standard.

The use of antimicrobial compounds specifically for growth-promotion purposes, as opposed to their use for control or treatment of bacterial infection, has also come under increased attention internationally because of rising concerns over antimicrobial resistance by pathogenic bacteria of concern in human medicine. Direct cause-effect evidence of antimicrobial use in livestock leading to bacterial resistance in human medicine is virtually nonexistent, requiring more complicated epidemiologic study. However, numerous studies have linked use of specific drugs in livestock, either for disease therapy or for growth-promotion purposes, to increased prevalence of drug resistance in target bacterial species. Results of these investigations are equivocal and have been the focal point of intense scrutiny and debate. In the absence of resoundingly clear cause-and-effect data, and because preservation of the continued efficacy of existing antimicrobial compounds is paramount, the cautionary principle has prevailed and will likely lead to greater restrictions on the use of antimicrobials for growth promotion in livestock and for therapeutic purposes as well.

Last full review/revision December 2013 by Christopher D. Reinhardt, BS, MS, PhD

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