Observations on the history of the development of antimicrobials and their use in poultry feeds.

Antimicrobials are powerful tools, but controversy and conflict often follow power. The development of antimicrobials was marked by personal attacks, political intrigue, internal conflicts, and lawsuits. Such controversy and conflict has continued. The early history of supplementing animal feeds with antimicrobials parallels the isolation and identification of vitamin B12. Vitamin B12 was isolated and characterized in 1948, but further research showed that several feed ingredients, including dried mycelia of certain fungi, were more potent as growth promoters in the diet of chicks than was vitamin B12 alone. The growth-promoting component in fungal mycelia was shown to have antimicrobial activity. A total of 32 antimicrobial compounds are approved for use in broiler feeds in the U.S. without a veterinary prescription. Fifteen compounds are listed for treatment of coccidiosis, 11 are listed as growth promotants, and six are listed for other purposes. Seven compounds are also used in human medicine. These compounds include bacitracin, chlotetracycline, erythromycin, lincomycin, novobiocin, oxytetracycline, and penicillin. No published estimates of antimicrobial use in animals exist at present, and estimates of that use differ markedly. The Union of Concerned Scientists (UCS) estimates usage at 30.6 million pounds, nearly 50% (49.85%) higher than the Animal Health Institute (AHI) estimate of 20.42 million pounds. AHI surveyed their members (the manufacturers of antimicrobials) to obtain their estimates, whereas USC calculated their estimates using published data and the following general formula: antimicrobial use = number of animals treated x average days treated x average dose.