A primary goal of animal producers worldwide is increased efficiency of conversion of feed into high-quality food products for humans, while minimizing risk to consumers. The physiologic mechanisms involved in converting feed into muscle, fat, and bone by animals are becoming more thoroughly understood. Consumer concerns about additives used for food production have focused on animal safety and well-being, organoleptic quality of the food, and potential health hazards to humans.
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.
Many commonly applied feed-grade antimicrobials have multiple applications, with growth promotion rarely listed as the sole indication. In the US, the FDA released the Guidance for Industry #213 in 2013, encouraging animal pharmaceutical companies to participate in voluntary removal of growth promotion claims from previously approved nonionophore feed-grade antimicrobial products. As such, the observed influence of nonionophore feed-grade antimicrobials on growth performance is not to be used as a marketing claim, even though treating clinical and subclinical illness can improve growth rate over nontreated animals.
Hormonal growth promotants include anabolic steroid hormones, growth hormone (GH), and insulin-like growth factor (IGF-I) used to augment endogenous GH concentrations. Anabolic steroid hormones are the class of hormonal growth promotants most widely used in production. They are almost exclusively used in cattle and only approved for use in ruminant species. In addition, beta-adrenergic receptor agonists are used to preferentially increase nutrient partitioning from fat to muscle ( See table Natural Steroid Hormone Growth Promotantsa).
Antimicrobial feed additives include those used to decrease populations of pathogenic bacteria in host GI tracts, compounds to manipulate ruminal fermentation by changing the ruminal microflora population in healthy animals, and probiotics to promote beneficial microflora in the GI tract.
Use of hormonal growth promotants and antimicrobial feed additives in production animals is controversial and is banned in some areas because of concerns about possible effects on humans, although the published literature supports their safety when used according to label claims.
The EU has banned beef produced use of growth-promotant implants since 1981. However, subsequent findings by the Lamming Committee (the European Economic Community's panel of scientific experts), the World Trade Organization, and the international Codex Alimentarius Commission indicate that appropriate use of approved growth-promoting hormones in animals poses no health risk to consumers.
Use of beta-adrenergic receptor agonists for growth promotion in beef, swine, and turkey production has come under scrutiny in the international meat trade community. The EU as well as Russia, China, and other countries have placed a total ban on meat from nations that allow the use of beta-adrenergic receptor agonists, whereas other countries have adopted the maximum residue limits (MRLs) as established by the Codex Alimentarius Commission. The FDA applies a greater MRL in the US than the Codex standard.
Use of antimicrobials specifically for growth-promotion purposes, as opposed to control or treatment of bacterial infection, has also come under increased attention internationally because of concerns over antimicrobial resistance by pathogenic bacteria of concern in human medicine. Numerous studies have linked use of specific drugs in production animals, either for disease treatment or for growth-promotion purposes, to increased prevalence of drug resistance in target bacterial species. However, evidence of a direct cause-effect relationship for antimicrobial use in production animals leading to antimicrobial resistance in human medicine requires further epidemiological study.
