Modern farmacology goes back to 1946:
In July 1946, the Journal of Biological Chemistry published a research paper out of the University of Wisconsin that detailed the results of feeding three antimicrobials to chickens. The summary included a crucial sentence: “Sulfasuxidine and streptomycin singly or in combination lead to increased growth responses in chicks receiving our basal diet supplemented with adequate amounts of folic acid.” That is, feeding antimicrobials to chickens made them grow faster.
Adding antimicrobials to chicken feed has its downsides:
In his 1945 Nobel Prize address, Alexander Fleming warned that it was easy to produce microbes resistant to his discovery, penicillin: Simply expose them to concentrations of the drug insufficient to kill them. Possibly the first warning that antibiotics could produce drug-resistant pathogens in poultry came as far back as 1951, when two bacteriologists at the University of California, Davis named Mortimer P. Starr and Donald M. Reynolds published a paper that noted in its summary: “The use of streptomycin as a growth-promoting supplement in turkey poults results in the appearance within three days of streptomycin-resistant coliform bacteria.” But little apparent attention was paid to Starr and Reynolds, or to Fleming. During ensuing decades, tens of millions of pounds of tetracycline, penicillin, and other antibiotics were fed to animals on American and European farms. In some cases, the drugs were used to treat sick animals, in amounts that killed the bacteria. But most were fed to cattle, pigs, turkeys, and chickens in exactly the subtherapeutic dosages that Fleming warned would only make bacteria stronger.
Antibiotic-resistance is a true public health issue — unlike the many not-at-all-public health issues under discussion recently.