Industrial animal farms commonly administer low doses of antibiotics and other antimicrobials (drugs that fight microorganisms like bacteria and viruses) to pigs, cows, chickens, sheep, and other food animal species for the purpose of growth promotion or weight gain. Typically, these sub-therapeutic doses, which are generally not high enough to fight active diseases or infections, are given directly to animals in their feed or water. In fact, it is common for feed to be pre-mixed with antimicrobial ingredients before it is purchased by livestock growers. The animals can receive additional, higher doses of these and other drugs again in their feed, water, or by injection for disease prevention and treatment.
The Food and Drug Administration (FDA) has the authority to collect information on drugs marketed to livestock producers, but the data collected from drug manufacturers has not been standardized and to date has been inadequate for effective monitoring and research purposes. Data have been provided on the anniversary of the drug approval date rather than a universal date each year for all drugs. There has been no standard for reporting the quantity sold (e.g., active ingredient vs. pill vs. bottle), or information on use by geography, species, or purpose (i.e., growth promotion, disease treatment, prevention due to exposure to sick animals). For these reasons, it is not known exactly how many antimicrobials are used on industrial animal farms for growth promotion. But, some estimate that perhaps as much as 70% of all antibiotics sold in the U.S. is given to cattle, swine, and poultry for purposes other than treating disease.1 Recently passed legislation will improve reporting from drug manufacturers, but there is still no requirement for industrial animal farms to report on actual drug use.
In spite of these limitations, the U.S. Department of Agriculture (USDA) has some sense of the way in which these antimicrobials are used on farms raising food animals. The USDA's Animal and Plant Health Inspection Service has conducted large-scale voluntary surveys of livestock health management practices, and has gathered and reported data on the use of antimicrobials in swine, beef cattle, and sheep.2 A similar survey of poultry producers did not contain such information.3 The survey of swine operations in seventeen states representing 94% of the industry revealed that 84% of swine farms gave antimicrobials to grower-finisher (i.e., weaned pre-slaughter) pigs in their feed for a variety of reasons; 55% did so for growth promotion alone. Similarly, 83% of cattle feedlots and 84% of sheep farms were found to administer antimicrobials in their feed or water for health or production reasons. These survey data were used to compile the ranking chart in PDF included with this issue brief.
Many of these feed or water additives are identical or closely related to antibiotic drugs used in human medicine to cure serious diseases. Penicillins, tetracyclines, macrolides, sulfonamides, and other antibiotic classes commonly fed to chickens, cows, pigs, sheep, turkeys, and other animals are used in people to treat pneumonia, scarlet fever, rheumatic fever, venereal disease, and infections of the lung, skin, eye, intestine, and more. In fact, the drug class used most commonly in animal feed – tetracyclines – is an important treatment or preventive for human pandemics like malaria and plague, as well as potential bioterrorism agents like smallpox and anthrax.
The use of human medicines on animal farms is contributing to the increase in antibiotic resistance both on the farm and in people.8 Antibiotic-resistant bacteria can enter the public sphere in three key ways: when animal waste carrying the bacteria contaminates the environment and drinking water supplies; when farm workers are exposed to the bacteria and pass it on to others; and when consumers purchase and improperly handle or cook meat or eggs containing the bacteria.9 (See Pew's fact sheet, “Antibiotic Resistant Bacteria in Animals and Unnecessary Human Health Risk.”) If human bacterial infection occurs, resistance to one or more antibiotics could as well, reducing the effectiveness of some life-saving drugs.10
This conflict between the need to maintain the effectiveness of antibiotics and their use to promote livestock weight gain continues to raise major concerns regarding escalating resistance. In February of 2007, a working group consisting of researchers and veterinarians from the conference on Environmental Health Impacts of Concentrated Animal Feeding Operations: Anticipating Hazards – Searching for Solutions considered the state of the science surrounding this important issue. Noting that “the industrialization of livestock production and the widespread use of nontherapeutic antimicrobial growth promotants has intensified the risk for emergence of new, more virulent, or more resistant microorganisms,” their recommendations included phasing out the practice of feeding antibiotics to animals as growth enhancers in the U.S.,11 as is already the case in the European Union, and as called for by the World Health Organization,12 the Institute of Medicine,13 and many scientific and public health organizations.14