IATP Hog Report - Institute for Agriculture and Trade Policy

Section 2
cure bacterial diseases but high enough to control them, is creating a
selective pressure on bacteria, causing them to develop resistance to the
antibiotics. When these resistant bacteria infect animals or people,
treatment with the same antibiotics (or close relatives of those antibiotics)
to which they have become resistant cannot kill them, imperiling the lives
of human and animal patients. According to NAS/NRC, up to 50 grams of
an antibiotic or antibiotics are added to a ton of animal feed to promote
growth in the animals eating it. 35 These are low levels, but they are
sufficient to allow resistance to develop. 36
Although subtherapeutic levels of antibiotics do not prevent bacterial
pathogens from infecting animals, they can prevent subclinically present
diseases from becoming clinical. 37 According to the National Research
Council: 38
The [disease control or prophylactic] effect is less
pronounced in clean, healthful, and stress-free
environments [while] beneficial effects of subtherapeutic
antibiotic feed additives are greatest in poor sanitary
conditions.
The disease controlling and growth-promoting effects of subtherapeutic
levels of antibiotics are strongest in herds on farms with low hygienic
standards and crowded, stressful conditions that put animals at a high risk
of infectious diseases. 39
Stress lowers animals' immunity levels. Antibiotics are perceived as
especially beneficial when animals are stressed either by intensive
husbandry or by shipment. 40
In the United States, nearly 30 antibiotics and chemotherapeutics are
approved for use in farm animals as subtherapeutic feed additives to
promote growth and increase the efficiency with which animals convert
feed to flesh. 41,42 Many of these same antimicrobials are also used
therapeutically to treat human and animal diseases. Eleven of them (for
example, penicillin and the tetracyclines) are identical to those used in
treatment of human disease. Feed additives also include the so-called
antibiotics of last resort for treatment of human diseases, such as
vancomycin.
Recently, the U.S. Animal Health Institute, a trade association
representing companies that develop and manufacture pharmaceuticals
and other animal health products, reported that 83% of feed additive
antibiotics are used for prevention and treatment of disease while only
6.1% are used for growth promotion. 43 On the face of it, these figures
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