INTRODUCTION
The use of antibiotic growth promoters (AGPs) in animal production began half a century ago, when
Stokstad and Jukes added residues of chlortetracycline production to chicken feed. They were
added with the objective to serve as a source of vitamin B12, but they caused a growth stimulation
that was far too large to be explained only as a vitamin effect (review by Brezoen et al., 1999). The
almost obvious cause lay in the antibiotic activity of the residues. This observation was quickly
extended to other antibiotics and to other animal species, leading to widespread adoption of AGP
inclusion in feeds.
During the last decades considerable amounts of antibiotics were used in animal production, both as
therapeutic and as growth promoting agents. Therapeutic usage of antibiotics is typically a high
dose-short term one, the substance being either injected, or administered via feed or water. Growthpromoting
usage is typically the opposite, i.e., a low dose-long term administration, usually given in
feed. A certain degree of overlapping exists of course between the two usages. Prophylactic usages,
while intentionally therapeutically, can resemble growth-promoting usages, and the latter can have a
degree of prophylactic action. On the other hand, growth promotion in short-lived species (e.g.
broilers) is necessarily short-term. In the former EU legislation, the two usages were strictly segregated.
AGPs were a small, and lately vanishing, subset of the whole antibiotic arsenal. Still, they more or
less consistently improved the production performances, with most of the economic benefits being
passed to consumers, via lower prices of meat, eggs, and other animal products. AGPs also had
secondary advantages, which are often forgotten. By decreasing feed usage per production unit,