a

GAO

United States General Accounting Office

Report to Congressional Requesters

April 2004 ANTIBIOTIC 

RESISTANCE

Federal Agencies 

Need to Better Focus 

Efforts to Address 

Risk to Humans from 

Antibiotic Use in 

Animals

GAO-04-490
www.gao.gov/cgi-bin/getrpt?GAO-04-490.

To view the full product, including the scope 

and methodology, click on the link above. 

For more information, contact Anu Mittal at 

(202) 512-3841 or Marcia Crosse at (202) 

512-7119. 

Highlights of GAO-04-490, a report to

congressional requesters 

April 2004

ANTIBIOTIC RESISTANCE 

Federal Agencies Need to Better Focus 

Efforts to Address Risk to Humans from 

Antibiotic Use in Animals

Scientific evidence has shown that certain bacteria that are resistant to 

antibiotics are transferred from animals to humans through the consumption 

or handling of meat that contains antibiotic-resistant bacteria. However, 

researchers disagree about the extent of harm to human health from this 

transference. Many studies have found that the use of antibiotics in animals 

poses significant risks for human health, but a small number of studies 

contend that the health risks of the transference are minimal. 

Federal agencies have expanded their efforts to assess the extent of 

antibiotic resistance, but the effectiveness of their efforts to reduce human 

health risk is not yet known. FDA, CDC, and USDA have increased their 

surveillance activities related to antibiotic resistance. In addition, FDA has 

taken administrative action to prohibit the use of a fluroquinolone in poultry. 

FDA has identified animal drugs that are critically important for human 

health and begun reviewing currently approved drugs using a risk 

assessment framework that it recently issued for determining the human 

health risks of animal antibiotics. However, because FDA’s initial reviews of 

approved animal drugs using this framework have focused on other drugs 

and have taken at least 2 years, FDA’s reviews of critically important drugs 

may not be completed for some time. 

Although federal agencies have made some progress in monitoring antibiotic 

resistance, they lack important data on antibiotic use in animals to support 

research on human health risks. These data, such as the type and quantity of 

antibiotics and purpose for their use by species, are needed to determine the 

linkages between antibiotic use in animals and emerging resistant bacteria. 

In addition, these data can help assess human health risks from this use and 

develop and evaluate strategies for mitigating resistance. 

The United States and several of its key agricultural trading partners and 

competitors differ in their use of antibiotics in animals in two important 

areas: the specific antibiotics allowed for growth promotion and availability 

of antibiotics to producers (by prescription or over the counter). For 

example, the United States and Canada allow some antibiotics important in 

human medicine to be used for growth promotion, but the European Union 

(EU) and New Zealand do not. Regarding over the counter sales of 

antibiotics, the United States is generally less restrictive than the EU. 

Antibiotic use in animals has not yet been a significant factor affecting U.S. 

international trade in meat and poultry, although the presence of antibiotic 

residues in meat has had some impact, according to government and 

industry officials. Instead, countries raise other food safety issues, such as 

hormone use and animal diseases. However, according to these officials, 

antibiotic use in animals may emerge as a factor in the future. They 

particularly noted that the EU could object to U.S. use of antibiotics for 

growth promotion as its member countries are phasing out that use. 

Antibiotic resistance is a growing 

public health concern; antibiotics 

used in animals raised for human 

consumption contributes to this 

problem. Three federal agencies 

address this issue—the Department 

of Health and Human Services’ 

(HHS) Food and Drug 

Administration (FDA) and Centers 

for Disease Control and Prevention 

(CDC), and the Department of 

Agriculture (USDA). GAO 

examined (1) scientific evidence on 

the transference of antibiotic 

resistance from animals to humans 

and extent of potential harm to 

human health, (2) agencies’ efforts 

to assess and address these risks, 

(3) the types of data needed to 

support research on these risks and 

extent to which the agencies 

collect these data, (4) use of 

antibiotics in animals in the United 

States compared with its key 

agricultural trading partners and 

competitors, and (5) information 

on how use has affected trade. 

GAO recommends that (1) FDA 

expedite its risk assessments of 

drugs used in animals that are 

critical for human health and 

(2) USDA and HHS develop and 

implement a plan to collect data on 

antibiotic use in animals. USDA 

and HHS generally agreed with 

GAO’s findings. With respect to the 

recommendations, HHS agreed that 

it is important to review animal 

drugs that are critical to human 

health and both agencies discussed 

ways to better collect antibiotic use 

data. 
Page i GAO-04-490 Antibiotic Use in Animals

Contents

Letter 1

Results in Brief 6

Background 8

Antibiotic-Resistant Bacteria Have Been Transferred from Animals 

to Humans, but Researchers Disagree About the Extent of 

Potential Harm to Human Health 17

Federal Agencies Have Increased Surveillance of Antibiotic 

Resistance from Animals to Assess Human Health Risk; 

Effectiveness of Risk Reduction Efforts Is Not Yet Known 27

Federal Agencies Do Not Collect Data Needed to Address the Risk 

of Antibiotic Resistance Associated with Use in Animals 39

The United States and Its Key Trading Partners and Competitors 

Differ in the Restrictions They Place on the Use of Antibiotics in 

Animals 43

Antibiotic Use in Animals Has Not Significantly Affected U.S. Trade 

but Could Be an Issue in the Future 45

Conclusions 47

Recommendations for Executive Action 48

Agency Comments and Our Response 49

Appendixes

Appendix I: Objectives, Scope, and Methodology 52

Appendix II: Studies of the Economic Impacts of Restricting Antibiotic 

Uses in Animals 57

Appendix III: FDA’s Procedures for Evaluating the Importance of an 

Animal Drug for Human Health 72

Appendix IV: Information on Selected Countries’ Activities to Address 

Animal-Related Antibiotic Resistance 73

Appendix V: Antibiotics Frequently Used in Animals 80

Antibiotic Use in U.S. Feedlot Cattle Production 80

Antibiotic Use in U.S. Swine Production 81

Antibiotic Use in U.S. Broiler Production 82

Appendix VI: Comments from the U.S. Department of Agriculture 84

GAO’s Responses to USDA’s Comments 87

Appendix VII: Comments from the Department of Health and Human 

Services 88
Contents

Page ii GAO-04-490 Antibiotic Use in Animals

Appendix VIII: GAO Contacts and Staff Acknowledgments 95

GAO Contacts 95

Acknowledgments 95

Tables Table 1: Federal Surveillance Activities Related to Antibiotic 

Resistance and Foodborne Disease or Animal Health 28

Table 2: Economic Studies That Estimate the Effects of 

Restrictions on Antibiotic Use 58

Table 3: Antibiotic Sales and Meat Production, 2002 73

Table 4: Antibiotics Frequently Used in Feedlot Cattle, 1999 81

Table 5: Antibiotics Frequently Used in Swine, 2000 82

Table 6: Antibiotics Frequently Used in Feed for Broiler Chickens, 

1995-2000 83

Figures Figure 1: Swine Confinement Facility 11

Figure 2: Possible Spread of Antibiotic-Resistant Bacteria from 

Animals to Humans 12

Figure 3: Sources of Data from Surveillance Activities about 

Antibiotic Resistance and Foodborne Disease or Animal 

Health 29
Contents

Page iii GAO-04-490 Antibiotic Use in Animals

Abbreviations

ADG average daily weight gain

ADP antibiotics used for disease prevention

AGP antibiotics used for growth promotion

CAHFSE Collaboration in Animal Health, Food Safety, and Epidemiology

CDC Centers for Disease Control and Prevention

DT definitive type

DNA deoxyribonucleic acid

EU European Union

FAO Food and Agriculture Organization of the United Nations

FAS Foreign Agricultural Service

FCR feed conversion ratio

FDA Food and Drug Administration

FoodNet Foodborne Diseases Active Surveillance Network

HIV human immunodeficiency virus

HHS Department of Health and Human Services

MR mortality rate

NAHMS National Animal Health Monitoring System

NARMS National Antimicrobial Resistance Monitoring System—Enteric 

Bacteria

NRC National Research Council

OIE Office International des Epizooties 

Q/D quinupristin/dalfopristin

USDA U.S. Department of Agriculture

WHO World Health Organization

WTO World Trade Organization

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Page 1 GAO-04-490 Antibiotic Use in Animals

United States General Accounting Office

Washington, D.C. 20548

A

April 22, 2004 Letr

The Honorable Olympia J. Snowe

Chair, Committee on Small Business and Entrepreneurship

United States Senate

The Honorable Tom Harkin

Ranking Democratic Member

Committee on Agriculture, Nutrition, and Forestry

United States Senate

The Honorable Edward M. Kennedy 

Ranking Minority Member

Committee on Health, Education, Labor, and Pensions

United States Senate 

Antibiotic resistance is a serious and growing public health problem.1 As 

resistance to antibiotics develops in disease-producing bacteria, it can 

become difficult to treat diseases that were formerly treatable with 

antibiotics, and this can have deadly consequences. Treating antibioticresistant infections often requires the use of more expensive drugs and can 

result in longer hospital stays. According to Institute of Medicine estimates, 

the annual cost of treating antibiotic-resistant infections may be as high as 

$3 billion. Experts cite the widespread use of antibiotics in human 

medicine as the principal cause of resistance, but they identify the use of 

antibiotics in animals raised for human consumption as contributing to 

antibiotic resistance in humans. It is generally agreed that a large 

proportion of the antibiotics used in the United States is administered to 

animals raised for human consumption.

While antibiotic use in animals poses potential human health risks, it also 

reduces the cost of producing these animals, which in turn helps reduce the 

prices consumers pay for food. Antibiotics are an integral part of animal 

production in the United States and many other countries where large 

numbers of livestock and poultry are raised in confined facilities, which 

increases the likelihood of disease. Antibiotics are used to treat animal 

1

Antibiotics are substances that destroy microorganisms or inhibit their growth. They are 

used extensively to treat bacterial infectious diseases in plants, animals, and humans. Some 

scientists refer to synthetic antibiotics as antimicrobials. In this report, we use the term 

antibiotics to mean both natural and synthetic types.
Page 2 GAO-04-490 Antibiotic Use in Animals

diseases; to prevent the spread of diseases that are known to occur during 

those phases of production when animals are at a high risk of disease (e.g., 

when animals have been transported to a new location); and to increase 

animals’ growth rate. Consumer groups argue that antibiotic use would be 

reduced if different animal production methods were used. Public health 

officials are particularly concerned about the use of antibiotics in animals 

to promote growth because antibiotics used for growth promotion are 

administered in low doses over long periods of time to large groups of 

animals that are not sick. This practice can allow animals to become 

reservoirs of antibiotic-resistant bacteria. If a person becomes ill from 

handling or ingesting meat or poultry contaminated with antibioticresistant bacteria, the infection may be resistant to treatment not only with 

the antibiotic of choice for that infection but also with other antibiotics in 

the same class of drugs. Use of antibiotics in animals also may lead to the 

transference of resistance from one type of bacteria to another type.

 Three federal agencies are primarily responsible for protecting Americans 

from the health risk associated with the transfer of antibiotic-resistant 

bacteria from meat and poultry to the humans who handle or consume 

these products. The Department of Health and Human Services’ (HHS) 

Food and Drug Administration (FDA) approves for sale and regulates the 

manufacture and distribution of antibiotics used in animals. HHS’s Centers 

for Disease Control and Prevention (CDC) conducts surveillance and other 

research to assess the extent of antibiotic resistance in humans from 

animals. The U.S. Department of Agriculture (USDA) gathers data on 

antibiotic resistance in animals, conducts surveillance, and funds 

epidemiologic and other research on antibiotic resistance in humans, 

animals, and the environment. In addition, internationally, the World Health 

Organization (WHO) and the Office International des Epizooties (OIE) have 

been examining these issues.2

2

The Office International des Epizooties is also known as the World Organization for Animal 

Health and, among other things, helps ensure the safety of foods produced from animals.
Page 3 GAO-04-490 Antibiotic Use in Animals

In 1999, we reported that the development and spread of antibioticresistant bacteria is a worldwide phenomenon and that the widespread use 

of various antibiotics has created the potential for U.S. public health costs 

to increase.3

 We further reported that the extent to which the agricultural 

use of antibiotics contributes to antibiotic-resistant bacteria in humans is 

uncertain and recommended that HHS and USDA work together to develop 

and implement a plan with specific goals, time frames, and resources 

needed for determining the safe use of antibiotics in agriculture.4

 In 

response, in January 2001, the federal Interagency Task Force on 

Antimicrobial Resistance, which is composed of FDA, CDC, and USDA, and 

several other agencies,5

 issued an action plan to address antibiotic 

resistance issues, including those associated with antibiotic use in animals. 

Subsequently, in June 2003, the task force issued a status report that 

described the agencies’ progress in implementing the activities outlined in 

the action plan.

You asked us to examine the (1) scientific evidence regarding the 

transference of antibiotic resistance from animals to humans through 

consuming or handling contaminated meat and poultry and the extent of 

potential harm to human health, (2) progress federal agencies have made in 

assessing and addressing the human health risk of antibiotic use in animals, 

(3) types of data that federal agencies need to support research on the 

human health risk of antibiotic use in animals and the extent to which these 

data are collected, (4) use of antibiotics in animals in the United States 

compared with antibiotic use by its key agricultural trading partners and 

competitors, and (5) information that is available on the degree to which 

antibiotic use in animals has affected U.S. trade. 

For the purpose of this report, the term “animal” refers to animals raised 

for human consumption, such as cattle, sheep, swine, chickens, and 

3

U.S. General Accounting Office, Antimicrobial Resistance: Data to Assess Public Health 

Threat from Resistant Bacteria Are Limited, GAO/HEHS/NSIAD/RCED-99-132

(Washington, D.C.: Apr. 28, 1999).

4

U.S. General Accounting Office, Food Safety: The Agricultural Use of Antibiotics and Its 

Implications for Human Health, GAO/RCED-99-74 (Washington, D.C.: Apr. 28, 1999).

5

The other task force agencies are the National Institutes of Health, the Agency for 

Healthcare Research and Quality, the Centers for Medicare and Medicaid Services, the 

Health Resources and Services Administration, the Department of Defense, the Department 

of Veterans Affairs, the Environmental Protection Agency, and since 2001, the U.S. Agency 

for International Development.
Page 4 GAO-04-490 Antibiotic Use in Animals

turkeys; the term “meat” refers to beef, lamb, pork, chicken, and turkey; 

and the term “contaminated meat” refers to meat that contains antibioticresistant bacteria. We limited the scope of our work to the transference of 

antibiotic-resistant bacteria from animals to humans through the 

consumption or handling of meat. Specifically, we looked at the evidence 

for transference of antibiotic-resistant foodborne intestinal pathogens from 

these animals to humans. We did not examine issues related to antibiotics 

used on plants and seafood, antibiotic residues in animals, or the effects of 

antibiotics present in the environment because of the application of animal 

waste to agricultural lands.

To identify scientific literature on the transmission of antibiotic-resistant 

bacteria from animals to humans, we searched medical, social science, and 

agricultural databases, which included HHS’s National Institutes of Health’s 

National Library of Medicine, for studies published in professional journals. 

We identified articles published since the 1970s on antibiotic use and 

resistance in animals and humans, as well as articles on antibiotic-resistant 

foodborne illnesses. 

To examine federal agencies’ progress in assessing and addressing the 

human health risk of antibiotic use in animals, we examined documents 

from FDA, CDC, and USDA. These documents include reports on results 

from the federal government’s antibiotic resistance surveillance program 

and on the progress of the federal Interagency Task Force on Antimicrobial 

Resistance, documents presented in an FDA administrative proceeding 

concerning the agency’s proposal to withdraw the approval of the use of a 

certain antibiotic used in poultry that is also an important antibiotic in 

human medicine, and FDA’s framework to assess the human health risk of 

antibiotic use in animals. 

To examine the types of data that federal agencies need on antibiotic use in 

animals to support research on the human health risk and the extent to 

which these data are collected, we reviewed federal agencies’ documents 

and reports and interviewed FDA, CDC, and USDA officials. We reviewed 

foreign government reports to determine how other countries use data on 

antibiotic use for research and international reports from WHO and OIE, 

which provide guidelines on the types of antibiotic use data that countries 

should collect. We also interviewed officials from Denmark, which collects 

extensive data on antibiotic use in animals, and from Canada, which plans 

to implement a data collection system. We discussed the availability of data 

on U.S. antibiotic use in animals with officials from pharmaceutical 
Page 5 GAO-04-490 Antibiotic Use in Animals

companies, industry associations, state veterinary offices, firms that collect 

data on antibiotic use in animals, and public health advocacy groups. 

To compare the United States’ use of antibiotics in animal production with 

that of its key trading partners and competitors, we reviewed information 

on antibiotic use in animals for these countries. We reviewed FDA 

regulations on antibiotic use in animals in the United States and visited 

livestock and poultry farms in Georgia, Maryland, and Pennsylvania. Using 

international trade data, we identified the European Union (EU) and 11 

countries—Australia, Brazil, Canada, China, Denmark,6

 Hong Kong, Japan, 

Mexico, New Zealand, Russia, and South Korea—as key U.S. trading 

partners or competitors. We identified relevant documents on these 

countries’ policies concerning antibiotic use in animals and obtained 

further information through discussions with USDA’s Foreign Agricultural 

Service officials, as well as through a questionnaire we sent to the agency’s 

attachés stationed in those countries. We examined these policies and 

identified the similarities and differences between countries. In addition, 

we discussed antibiotic use and policies with government officials from 

Canada, a leading U.S. trading partner and competitor, and Denmark, a 

leading U.S. trading partner and competitor that took significant actions to 

curtail antibiotic use in animals during the late 1990s. We also reviewed 

USDA and other reports on antibiotic use in animal production. We did not 

independently verify the information we received in response to our 

questionnaire; other documents, including laws and regulations from the 

foreign countries; or other reports on antibiotic use in the United States. 

To examine the available information on the degree to which antibiotic use 

in animals has affected U.S. trade, we examined USDA records on foreign 

countries’ meat import standards and reviewed reports by USDA and 

international food safety organizations on international trade issues related 

to food safety. In addition, we discussed international trade issues with 

officials from the Office of the U.S. Trade Representative, USDA’s Foreign 

Agricultural Service, and meat industry trade associations.

We discussed the matters in this report with government officials, public 

interest groups, pharmaceutical manufacturers, and international and 

academic experts. Appendix I provides additional information on our 

scope and methodology. We conducted our work from May 2003 through 

6

Although Denmark is an EU member, we included it in addition to the EU because it is a 

major U.S. competitor in pork exports.
Page 6 GAO-04-490 Antibiotic Use in Animals

April 2004 in accordance with generally accepted government auditing 

standards. 

Results in Brief Antibiotic-resistant bacteria have been transferred from animals to 

humans, and many of the studies we reviewed found that this transference 

poses significant risks for human health. Studies have shown two types of 

evidence related to the transfer of antibiotic-resistant bacteria from 

animals to humans. First, some studies have provided evidence of 

associations between changes in antibiotic use in animals and resistance to 

antibiotics in humans. For example, researchers have found that antibioticresistant Escherichia coli (E. coli) and campylobacter bacteria increased 

in humans as use of the antibiotics commonly used to treat infections 

caused by those bacteria has increased in animals. Second, studies that 

have examined the genetic makeup of the bacteria have provided evidence 

of a stronger link and have established that antibiotic-resistant 

campylobacter and salmonella bacteria are transferred from animals to 

humans. In those studies, strains of antibiotic-resistant bacteria infecting 

humans were indistinguishable from those found in animals, leading the 

researchers to conclude that the animals were the source of infection. 

Researchers disagree about the extent of the human health risk caused by 

this transference. Many studies have found that the use of antibiotics in 

animals poses significant risks for human health. However, a small number 

of studies contend that health risks of the transference are minimal.

Federal agencies have expanded their surveillance of antibiotic resistance 

from the use of antibiotics in animals to assess the risk to human health, 

but it is too early to determine the effectiveness of their efforts to reduce 

this risk. FDA, CDC, and USDA have increased their surveillance activities 

related to antibiotic resistance in animals, humans, and retail meat by 

studying more types of bacteria, increasing the geographic areas studied, 

and adding new programs. In addition, all three agencies have funded or 

conducted research on antibiotic resistance in animals. As the regulatory 

agency responsible for animal drugs, FDA has determined that antibiotic 

resistance in humans resulting from the use of antibiotics in animals is an 

unacceptable risk to the public health and has taken a variety of recent 

actions. For example, FDA has taken action to prohibit the use of the 

fluoroquinolone antibiotic enrofloxacin in poultry because of what the 

agency asserts is strong evidence that the use of these antibiotics has led to 

the transference of antibiotic-resistant bacterial diseases from poultry to 

humans. A challenge from the drug’s manufacturer has led to 

administrative proceedings that have lasted more than 3 years, and the 
Page 7 GAO-04-490 Antibiotic Use in Animals

product remains on the market pending the final outcome of this case. In 

addition, FDA has issued guidance recommending a risk assessment 

framework for determining the human health risk of animal antibiotics and 

has begun to apply this framework in its reviews of manufacturers’ 

applications for approval of new animal drugs. FDA has also begun 

reviewing currently approved animal antibiotics using this same 

framework. However, the approved drugs that it has reviewed to date using 

this approach have not included those that FDA identified in its guidance as 

critically important to human health, and the reviews have taken at least 2 

years to complete. Therefore it may be some time before FDA completes its 

reviews of critically important drugs in order to determine if enforcement 

action to protect human health is warranted. 

Although they have made some progress in monitoring antibiotic 

resistance, federal agencies do not collect the critical data on antibiotic use 

in animals that they need to support research on the human health risk. The 

data that could help this research include the types and quantities of 

antibiotics sold for use in animals, the purpose of their use (such as disease 

treatment or growth promotion), the species in which they are used, and 

the method used to administer them. These types of data are needed to 

study the linkages between antibiotic use in animals and the human risk 

from antibiotic resistance and to develop and evaluate strategies for 

mitigating resistance. Such data could also help researchers assess the 

human risk from using antibiotics in animals. At this time, FDA is not 

collecting data on antibiotic use in animals, and USDA’s data collection 

activities are limited to a few swine farms. In Denmark, where detailed data 

on antibiotic use are collected, scientists have been able to research the 

effects of antibiotic use in animals on the development of resistant bacteria 

in animals, food, and humans and to develop mitigation strategies that 

minimize the potential human health risk. 

The United States and several of its key trading partners and competitors, 

such as the EU, Canada, Australia, South Korea, and New Zealand, differ in 

their use of antibiotics in animals in two key areas: the specific antibiotics 

that can be used for growth promotion and the availability of antibiotics to 

producers (by prescription or over the counter). For example, the United 

States and Canada allow some antibiotics important in human medicine to 

be used for growth promotion. In contrast, New Zealand and the EU have 

banned this use in feed for those antibiotics that are important in human 

medicine. The EU has also issued a regulation requiring that member 

nations prohibit the use of all other antibiotics in feed for growth 

promotion by 2006. With regard to the availability of antibiotics to 
Page 8 GAO-04-490 Antibiotic Use in Animals

producers, the United States allows older antibiotics to be sold over the 

counter but requires a veterinarian’s prescription for newer antibiotics, 

such as fluoroquinolones. Some other countries, including Canada, also 

allow certain antibiotics to be sold over the counter. In contrast, Danish 

producers need prescriptions for all antibiotics, while other EU countries 

generally require prescriptions. 

To date, antibiotic use in animals has not been a significant factor affecting 

the United States’ international trade in meat products, although the 

presence of antibiotic residues in meat has had some impact, according to 

officials from USDA, the Office of the U.S. Trade Representative, and 

industry. In addition, these officials told us, foreign governments have 

raised other food safety concerns as trade issues, including hormone use in 

animals and animal diseases, such as bovine spongiform encephalopathy 

(commonly known as mad cow disease) and avian influenza. However, 

according to government officials, a USDA report, and a Canadian 

government report, antibiotic use in animals may emerge as a factor in U.S. 

trade negotiations in the future. The officials particularly noted that the EU 

could object to the United States’ use of antibiotics for growth promotion 

because member countries are phasing out that use. 

We are making recommendations to federal agencies to better focus their 

efforts to reduce the risk to human health from the transfer of antibioticresistant bacteria from meat. We recommend that FDA expedite its risk 

assessments of the antibiotics used in animals that are critically important 

to human health to determine if regulatory action is necessary. We also 

recommend that the Secretaries of Agriculture and of Health and Human 

Services develop and implement a plan to collect data on antibiotic use in 

animals that will adequately (1) support research on the relationship 

between this kind of antibiotic use and emerging resistant bacteria, (2) help 

assess the human health risk related to antibiotic use in animals, and (3) 

help the agencies develop and evaluate strategies to mitigate antibiotic 

resistance. 

In commenting on a draft of this report, USDA and HHS generally agreed 

with our findings. With respect to our recommendations, HHS agreed that it 

is important to review animal drugs that are critical for human health, and 

both agencies discussed ways to better collect antibiotic use data. 

Background For over 50 years, antibiotics have been widely prescribed to treat bacterial 

infections in humans. Many antibiotics commonly used in humans have 
Page 9 GAO-04-490 Antibiotic Use in Animals

also been used in animals for therapeutic and other purposes, including 

growth promotion. Resistance to penicillin, which was the first broadly 

used antibiotic, started to emerge soon after its widespread introduction. 

Since that time, resistance to other antibiotics has emerged, and antibiotic 

resistance has become an increasing public health problem worldwide.

Development of Antibiotic 

Resistance

Antibiotics kill most, if not all, of the susceptible bacteria that are causing 

an infection, but leave behind—or select, in biologic terms—the bacteria 

that have developed resistance, which can then multiply and thrive. 

Infection-causing bacteria that were formerly susceptible to an antibiotic 

can develop resistance through changes in their genetic material, or 

deoxyribonucleic acid (DNA). These changes can include the transfer of 

DNA from resistant bacteria, as well as spontaneous changes, or mutations, 

in a bacterium’s own DNA. The DNA coding for antibiotic resistance is 

located on the chromosome or plasmid of a bacterium.7

 Plasmid-based 

resistance is transferred more readily than chromosomal-based resistance. 

Once acquired, the genetically determined antibiotic resistance is passed 

on to future generations and sometimes to other bacterial species. The 

dose of antibiotic and length of time bacteria are exposed to the antibiotic 

are major factors affecting whether the resistant bacteria population will 

dominate. Low doses of antibiotics administered over long periods of time 

to large groups of animals, such as doses used for growth promotion in 

animals, favor the emergence of resistant bacteria.8

Investigating the Impact of 

Antibiotic Resistance on 

Human Health

To investigate the impact on human health of antibiotic use in animals, 

researchers have used both epidemiologic studies alone and epidemiologic 

studies combined with molecular subtyping of bacterial isolates.9

Epidemiologic studies examine patterns of health or disease in a 

population and the factors that influence these patterns. These studies help 

to identify the cause of a disease and the factors that influence a person’s 

7

Chromosomes are linear threads made of DNA in the nucleus of a cell. Plasmids are 

circular pieces of DNA that are smaller than chromosomes and are often called extra- or 

mini-chromosomes.

8

Stuart B. Levy, “Multidrug Resistance—A Sign of the Times,” New England Journal of 

Medicine, vol. 338, no. 19 (1998): 1376-1378.

9

A bacterial isolate is a population of organisms that come from a sample, such as diseased 

tissue from animals or humans.
Page 10 GAO-04-490 Antibiotic Use in Animals

risk of infection. Many studies investigating antibiotic-resistant bacteria 

and their impact on human health combine epidemiologic studies with 

molecular subtyping—also called “DNA fingerprinting”—a technique that 

translates bacteria’s genetic material into a “bar code” that can be used to 

identify specific pathogens and link them with disease outbreaks. For 

example, following an outbreak of a diarrheal disease among people in a 

community, an epidemiologic study would determine all the common 

exposures among the people with the disease, and molecular subtyping of 

bacterial isolates could determine what pathogens were responsible for the 

disease.

Use of Antibiotics in 

Animals

While the use of antibiotics in animals poses potential human health risk, it 

is also an integral part of intensive animal production in which large 

numbers of poultry, swine, and cattle are raised in confinement facilities. 

(See fig. 1.) Antibiotics are used in animals to treat disease; to control the 

spread of a disease in a group of animals when disease is present in some of 

the animals; to prevent diseases that are known to occur during high-risk 

periods, such as after transport, when the animals are stressed; and to 

promote growth—that is, to allow animals to grow at a faster rate while 

requiring less feed per pound of weight gain.10 This use of antibiotics is 

commonly referred to as growth promotion and generally entails using low 

doses of antibiotics over long periods of time in large groups of animals. 

Many animal producers believe the use of antibiotics for growth promotion 

also prevents disease. Antibiotics are generally administered by injection to 

individual animals and in feed or water to groups of animals. 

10Although scientists do not fully understand how antibiotics promote growth in animals, 

they believe antibiotics work through mechanisms such as increasing the absorption of 

nutrients in feed and suppressing subclinical bacterial infections.
Page 11 GAO-04-490 Antibiotic Use in Animals

Figure 1: Swine Confinement Facility

Possible Spread of 

Antibiotic-Resistant 

Bacteria from Animals to 

Humans

Figure 2 shows how antibiotic-resistant bacteria that develop in animals 

can possibly be transferred to humans, who may then develop a foodborne 

illness, such as a salmonella infection, that is resistant to antibiotic 

treatment.11 Once the resistant bacteria develop in animals, they may be 

passed to humans through the consumption or handling of contaminated 

meat. An animal or human may carry antibiotic-resistant bacteria but show 

no signs or symptoms of an illness. Resistant bacteria may also be spread 

to fruits, vegetables, and fish products through soil, well water, and water 

runoff contaminated by waste material from animals harboring these 

bacteria, although such routes are beyond the focus of this report.

11Foodborne illnesses generally cause gastrointestinal symptoms, such as nausea, vomiting, 

abdominal cramps, and diarrhea. There are more than 250 foodborne diseases, and most are 

caused by bacteria, viruses, and parasites.
Page 12 GAO-04-490 Antibiotic Use in Animals

Figure 2: Possible Spread of Antibiotic-Resistant Bacteria from Animals to Humans

Bacterial population

(resistant and susceptible)

in farm animals

Antibiotic drug is given to animal 

to prevent or treat disease

Animal is given feed or water 

treated with antibiotics for 

growth promotion

Antibiotic selects for resistant bacteria

Resistant disease or infection may develop in humans

Resistant bacteria in animal may or may not cause 

disease or infection

Bacteria transfer resistance genes to other bacteria

Spread of resistant bacteria 

to consumers via contaminated 

meat products

Spread of resistant bacteria 

to farm workers and food 

processors via handling of 

contaminated animals or meat

Source: GAO. 

Area of concern in this report

Spread of resistant bacteria 

to other animals on the farm 

via interaction with contaminated 

animals

Spread of resistant bacteria 

to soil, well water, and water 

runoff via contaminated animal 

waste

Spread of resistant 

bacteria to fruits and 

vegetables

Spread of resistant 

bacteria 

to fish
Page 13 GAO-04-490 Antibiotic Use in Animals

Debate Regarding Public 

Health Impact of Use of 

Antibiotics in Agriculture

Researchers in human medicine have debated the public health impact of 

antibiotic use in agriculture for many years. In the United States the debate 

intensified before FDA approved the first fluoroquinolone antibiotic for use 

in animals in 1995. At that time, drugs from the fluoroquinolone class had 

already been used for humans for nearly a decade. Debate focused on 

whether development of resistance to the drug approved for use in animals 

could, through cross-resistance,12 compromise the effectiveness of other 

drugs in the fluoroquinolone class that were valuable in treating human 

diseases.

Efforts have been made to address the spread of antibiotic resistance by 

providing education to change behaviors of physicians and the public, but 

researchers differ on whether changes in agricultural practices are also 

needed. CDC has undertaken educational efforts aimed at physicians and 

the public. CDC is encouraging physicians to reduce prescribing antibiotics 

for infections commonly caused by viruses, such as ear and sinus 

infections. Patients are being taught that antibiotics are only for bacterial 

infections, not viral infections. Many researchers contend that efforts to 

reduce the use of antibiotics in animals are also needed to preserve the 

effectiveness of antibiotics necessary for treatment of bacterial diseases in 

humans and animals and to decrease the pool of resistant bacteria in the 

environment. However, agricultural industry officials argue that antibiotic 

use in animals is essential to maintaining the health of animals and 

therefore the safety of food.

12Cross-resistance is the phenomenon in which a microbe, such as a bacterium, that has 

acquired resistance to one drug through direct exposure, also turns out to have resistance to 

one or more other drugs, typically in the same drug class, to which it has not been exposed.
Page 14 GAO-04-490 Antibiotic Use in Animals

Professional organizations and associations differ on the use of antibiotics 

in animals. Many professional organizations that have studied the human 

health implications of antibiotic use in animals—including WHO and, in the 

United States, the Institute of Medicine of the National Academy of 

Sciences and the Alliance for the Prudent Use of Antibiotics—have 

recommended either limiting or discontinuing the use of antibiotic growth 

promoters.13 Many of the professional associations for human medicine—

such as the American Medical Association, the American College of 

Preventive Medicine, the American Public Health Association, and the 

Council of State and Territorial Epidemiologists—have position statements 

for limiting antibiotic use in animals for nontherapeutic purposes, such as 

growth promotion, for antibiotics that are important for both human and 

animal health. Many of the professional associations for veterinary 

medicine—such as the American Veterinary Medical Association and the 

American Association of Swine Practitioners—agree on the goal of 

reducing the use of antibiotics in animals but differ on the means to achieve 

this goal. These associations are calling for veterinarians to work with 

owners of animals to implement judicious use guidelines.

While limiting the use of antibiotics in animals for growth promotion may 

reduce the human health risk associated with antibiotic-resistant bacteria, 

such restrictions also may increase the cost of producing animals and the 

prices consumers pay for animal products. For example, a 1999 economic 

study estimated that a hypothetical ban on all antibiotic use in feed in 

swine production would increase U.S. consumers’ costs by more than $700 

million per year.14,15 However, the increase in consumer costs would be 

much smaller if—as the Institute of Medicine proposed in 2003—producers 

were allowed to continue to use some antibiotics for growth promotion and 

13World Health Organization, Department of Communicable Disease Surveillance and 

Response, WHO Global Principles for the Containment of Antimicrobial Resistance in 

Animals Intended for Food (Geneva, Switzerland, 2000); Alliance for the Prudent Use of 

Antibiotics, “The Need to Improve Antimicrobial Use in Agriculture: Ecological and Human 

Health Consequences.” Clinical Infectious Diseases, vol. 34, suppl. 3 (2002): S76-S77; and 

Institute of Medicine of the National Academies of Sciences, Microbial Threats to Health: 

Emergence, Detection, and Response (Washington, D.C., 2003): 16-17.

14Dermot J. Hayes, Helen H. Jensen, Lennart Backstrom, and Jay Fabiosa, “Economic 

Impact of a Ban on the Use of Over-the-Counter Antibiotics,” Staff Report 99-SR 90, Center 

for Agricultural and Rural Development, Iowa State University, Ames, Iowa, December 1999.

15However, FDA’s authority to withdraw a currently approved animal antibiotic use is 

generally limited to human health considerations and does not concern the economic 

impacts of such a withdrawal. See 21 U.S.C. §360b(e)(2000).
Page 15 GAO-04-490 Antibiotic Use in Animals

only antibiotics that are used in humans were banned for growth 

promotion. Moreover, in other animal species, such as beef cattle or 

chickens, the economic impacts of growth promotion restrictions would 

likely be smaller than in swine because antibiotic use for growth promotion 

is less prevalent in the production of these other species. Appendix II 

summarizes studies of the economic effects of banning antibiotic use for 

growth promotion and other proposed restrictions on antibiotic uses in 

animals.

Federal Agency 

Responsibilities and 

Authority

The three federal agencies responsible for protecting Americans from 

health risk associated with drug use in animals are FDA, CDC, and USDA. 

These agencies have a variety of responsibilities related to surveillance, 

research, and regulation. All three agencies collaborate on surveillance 

activities, such as the National Antimicrobial Resistance Monitoring 

System—Enteric Bacteria (NARMS), which was initiated in 1996 because 

of public health concerns associated with the use of antibiotics in animals. 

In addition, FDA’s primary responsibilities as a regulatory body focus on 

human health and animal drug safety. CDC primarily conducts research and 

education that focus on human health. USDA oversees the retail meat 

trade, including related farm and slaughter operations. USDA activities may 

include studies of healthy farm animals, evaluations of diagnostic data 

involving sick animals, and biological sampling from slaughter and meat 

processing plants. USDA also conducts research and education related to 

antibiotic resistance.

In addition, FDA approves for sale and regulates the manufacture and 

distribution of drugs used in veterinary medicine, including drugs given to 

animals from which human foods are derived. Prior to approving a new 

animal drug application, FDA must determine that the drug is safe and 

effective for its intended use in the animal. It must also determine that the 

new drug intended for animals is safe with regard to human health. FDA 

considers a new animal antibiotic to be safe if it concludes that there is 

reasonable certainty of no harm to human health from the proposed use of 

the drug in animals. FDA may also take action to withdraw an animal drug 

from the market when the drug is no longer shown to be safe.16

1621 U.S.C. §360b(e)(1)(2000).
Page 16 GAO-04-490 Antibiotic Use in Animals

These three agencies also participate in the federal Interagency Task Force 

on Antimicrobial Resistance. Task force activities focus on antibiotic 

resistance from use of antibiotics in animals, as well as the human use of 

antibiotics. In January 2001, the task force developed an action plan based 

on advice from consultants from state and local health agencies, 

universities, professional societies, pharmaceutical companies, health care 

delivery organizations, agricultural producers, consumer groups, and other 

members of the public. The action plan includes 84 action items, 13 of 

which have been designated as top-priority items and cover issues of 

surveillance, prevention and control, research, and product development.17

A federal agency (or agencies) is designated as the lead for each action 

item. 

International Trade Issues The United States is one of the world’s leading exporters of meat. In 2002, 

U.S. meat exports accounted for about $7 billion. The World Trade 

Organization (WTO), of which the United States is a member, provides the 

institutional framework for conducting international trade, including trade 

in meat products. WTO member countries agree to a series of rights and 

obligations that are designed to facilitate global trade. When a country 

regulates imports, including imported meat, WTO guidelines stipulate that 

member countries have the right to determine their own “appropriate levels 

of protection” in their regulations to protect, among other things, human 

and animal health. Member countries must have a scientific basis to have 

levels of protection that are higher than international guidelines. To 

encourage member countries to apply science-based measures in their 

regulations, WTO relies on the international standards, guidelines, and 

recommendations that its member countries develop within international 

organizations, such as the Codex Alimentarius Commission for food safety 

and the OIE for animal health and the safety of animal products for human 

consumption. 

While ensuring that food products are safe and of high quality usually 

promotes trade, one country’s food safety regulations could be interpreted 

by another country as a barrier to trade. It is difficult, however, to 

distinguish between a legitimate regulation that protects consumers but 

incidentally restricts trade from a regulation that is intended to restrict 

17See http://www.cdc.gov/drugresistance/actionplan/ (downloaded Apr. 11, 2003).
Page 17 GAO-04-490 Antibiotic Use in Animals

trade and protect local producers, unless that regulation is scientifically 

documented.

Antibiotic-Resistant 

Bacteria Have Been 

Transferred from 

Animals to Humans, 

but Researchers 

Disagree About the 

Extent of Potential 

Harm to Human Health

Research has shown that antibiotic-resistant bacteria have been 

transferred from animals to humans, but the extent of potential harm to 

human health is uncertain. Evidence from epidemiologic studies suggests 

associations between patterns of antibiotic resistance in humans and 

changes in antibiotic use in animals. Further, evidence from epidemiologic 

studies that include molecular subtyping to identify specific pathogens has 

established that antibiotic-resistant campylobacter and salmonella bacteria 

are transferred from animals to humans. Many of the studies we reviewed 

found that this transference poses significant risks for human health. 

Researchers disagree, however, about the extent of potential harm to 

human health from the transference of antibiotic-resistant bacteria. 

Antibiotic-Resistant 

Bacteria Have Been 

Transferred from Animals to 

Humans

Antibiotic-resistant bacteria have been transferred from animals to 

humans. Evidence that suggests that this transference has taken place is 

found in epidemiologic studies showing that antibiotic-resistant E. coli and 

campylobacter bacteria in humans increase as use of the antibiotics 

increases in animals. Evidence that establishes transference of antibioticresistant bacteria is found in epidemiologic studies that include molecular 

subtyping. These studies have demonstrated that antibiotic-resistant 

campylobacter and salmonella bacteria have been transferred from animals 

to humans through the consumption or handling of contaminated meat. 

That is, strains of antibiotic-resistant bacteria infecting humans were 

indistinguishable from those found in animals, and the researchers 

concluded that the animals were the source of infection.
Page 18 GAO-04-490 Antibiotic Use in Animals

Epidemiologic Evidence 

Suggests That Patterns of 

Antibiotic Resistance in Humans 

Are Associated with Changes in 

Antibiotic Use in Animals

Evidence from epidemiologic studies that do not include molecular 

subtyping indicates that patterns of antibiotic resistance in humans are 

associated with changes in the use of particular antibiotics in animals. For 

example, work conducted in the United States in the 1970s showed an 

association between the use of antibiotic-supplemented animal feed in a 

farm environment and the development of antibiotic-resistant E. coli in the 

intestinal tracts of humans and animals.18 In the study, isolates from 

chickens on the farm and from people who lived on or near the farm were 

tested and found to have low initial levels of tetracycline-resistant E. coli 

bacteria. The chickens were then fed tetracycline-supplemented feed, and 

within 2 weeks 90 percent of them were excreting essentially all 

tetracycline-resistant E. coli bacteria. Within 6 months, 7 of the 11 people 

who lived on or near the farm were excreting high numbers of resistant E. 

coli bacteria. Six months after the tetracycline-supplemented feed was 

removed, no detectable tetracycline-resistant organisms were found in 8 of 

the 10 people who lived on or near the farm when they were retested. 

Another study,19 based on human isolates of Campylobacter jejuni

submitted to the Minnesota Department of Health, reported that the 

percentage of Campylobacter jejuni in the isolates that were resistant to 

quinolone increased from approximately 0.8 percent in 1996 to 

approximately 3 percent in 1998.20

18Stuart B. Levy, George B. Fitzgerald, and Ann B. Macone, “Spread of Antibiotic-Resistant 

Plasmids from Chicken to Chicken and from Chicken to Man,” Nature, vol. 260, no. 5546 

(1976): 40-42; and Stuart B. Levy, George B. Fitgerald, and Ann B. Macone, “Changes in 

Intestinal Flora of Farm Personnel after Introduction of a Tetracycline-Supplemented Feed 

on a Farm,” New England Journal of Medicine, vol. 295 (1976): 583-588.

19Kirk E. Smith, John M. Besser, Craig W. Hedberg, Fe T. Leano, Jeffrey B. Bender, Julie H. 

Wicklund, Brian P. Johnson, Kristine A. Moore, Michael T. Osterholm, and the investigation 

team, “Quinolone-resistant Campylobacter jejuni infections in Minnesota, 1992-1998,” New 

England Journal of Medicine, vol. 340, no. 20 (1999). 

20These percentages are from isolates from people who acquired the infections in the United 

States. There was a greater increase in the number of quinolone-resistant human isolates 

when infections acquired from foreign travel and from people who took fluoroquinolones 

prior to the collection of stool samples were included. Noting this, the percentage change 

between 1996 and 1998 of the domestically acquired infections was found to be statistically 

significant. FDA approved the use of fluoroquinolones in animals in 1995.
Page 19 GAO-04-490 Antibiotic Use in Animals

There is also evidence to suggest that antibiotic-resistant enterococcus has 

developed from the use of antibiotics in animals. Vancomycin21 resistance 

is common in intestinal enterococci of both exposed animals and 

nonhospitalized humans only in countries that use or have previously used 

avoparcin (an antibiotic similar to vancomycin) 22 as an antibiotic growth 

promoter in animal agriculture.23 Since the EU banned the use of avoparcin 

as a growth promoter, several European countries have observed a 

significant decrease in the prevalence of vancomycin-resistant enterococci 

in meat and fecal samples of animals and humans.

Evidence Shows That 

Antibiotic-Resistant 

Campylobacter and 

Salmonella Bacteria Have 

Been Transferred to 

Humans

Epidemiologic studies that include molecular subtyping have demonstrated 

that antibiotic-resistant campylobacter and salmonella bacteria have been 

transferred from animals to humans through the consumption or handling 

of contaminated meat. That is, strains of antibiotic-resistant bacteria 

infecting humans were indistinguishable from those found in animals, and 

the authors of the studies concluded that the animals were the source of 

infection.

Campylobacter Bacteria The strongest evidence for the transfer of antibiotic-resistant bacteria from 

animals to humans is found in the case of fluoroquinolone-resistant 

campylobacter bacteria. Campylobacter is one of the most commonly 

identified bacterial causes of diarrheal illness in humans. The strength of 

the evidence is derived in part from the fact that the particular way 

fluoroquinolone resistance develops for campylobacter bacteria makes it 

easier to identify the potential source of the resistance. Most chickens are 

colonized with campylobacter bacteria, which they harbor in their 

intestines, but which do not make them sick. Fluoroquinolones are given to 

flocks of chickens when some birds are found to have certain infections 

caused by E. coli. In addition to targeting the bacteria causing the infection, 

treatment of these infections with fluoroquinolones almost always replaces 

susceptible campylobacter bacteria with fluoroquinolone-resistant 

campylobacter bacteria. Because fluoroquinolone resistance is located on 

21The antibiotic vancomycin has been reserved to treat infections, such as enterococcus 

infections, in humans that are resistant to antibiotics normally used for treatment.

22Avoparcin has never been approved for food animal use in the United States.

23Anthony E. van den Bogaard and Ellen E. Stobberingh, “Epidemiology of Resistance to 

Antibiotics Links between Animals and Humans,” International Journal of Antimicrobial 

Agents, vol. 14 (2000): 327-335.
Page 20 GAO-04-490 Antibiotic Use in Animals

the chromosome of campylobacter, the resistance is generally not 

transferred to other species of bacteria. Therefore when fluoroquinoloneresistant campylobacter bacteria are detected in human isolates, the 

source is likely to be other reservoirs of campylobacter bacteria, including 

animals. In some cases, molecular subtyping techniques have shown that 

fluoroquinolone-resistant isolates of campylobacter from food, humans, 

and animals are similar. 

Fluoroquinolone-resistant Campylobacter jejuni in humans has increased 

in the United States and has been linked with fluoroquinolone use in 

animals. CDC reported that in the United States the percentage of 

Campylobacter jejuni in human isolates that were resistant to 

fluoroquinolones increased from 13 percent in 1997 to 19 percent in 2001.24

A study in Minnesota found that fluoroquinolone-resistant Campylobacter 

jejuni was isolated from 14 percent of 91 chicken products obtained from 

retail markets in 1997.25 Through molecular subtyping, the strains isolated 

from the chicken products were shown to be the same as those isolated 

from nearby residents, thereby bolstering the case that the chickens were 

the source of the antibiotic resistance. 

During the 1980s, the resistance of campylobacter bacteria to 

fluoroquinolones increased in Europe. European investigators 

hypothesized that there was a causal relationship between the use of 

fluoroquinolones in animals and the increase in fluoroquinolone-resistant 

campylobacter infections in humans. For example, an epidemologic study 

that included molecular subtyping in the Netherlands found that among 

different strains of campylobacter bacteria, the percentage of 

fluoroquinolone-resistant strains in isolates tested had risen from 0 percent 

in both human and animal isolates in 1982 to 11 percent in human isolates 

and 14 percent in poultry isolates by 1989.26 The authors concluded that the 

24Centers for Disease Control and Prevention, National Antimicrobial Resistance 

Monitoring System: Enteric Bacteria 2001 Annual Report (2003): 10.

25Kirk E. Smith, John M. Besser, Craig W. Hedberg, Fe T. Leano, Jeffrey B. Bender, Julie H. 

Wicklund, Brian P. Johnson, Kristine A. Moore, Michael T. Osterholm, and the investigation 

team, “Quinolone-resistant Campylobacter jejuni Infections in Minnesota, 1992-1998,” New 

England Journal of Medicine, vol. 340, no. 20 (1999).

26Hubert Ph. Endtz, Gijs J. Ruijs, Bert van Klingeren, Wim H. Jansen, Tanny van der Reyden, 

and R. Peter Mouton, “Quinolone Resistance in Campylobacter Isolated from Man and 

Poultry Following the Introduction of Fluoroquinolones in Veterinary Medicine,” Journal of 

Antimicrobial Chemotherapy, vol. 27 (1991): 199-208.
Page 21 GAO-04-490 Antibiotic Use in Animals

use of two new fluoroquinolones, one in humans in 1985 and one in animals 

in 1987, was responsible for the quinolone-resistant strains. The authors 

asserted that the extensive use of fluoroquinolones in poultry and the 

common route of campylobacter infection from chickens to humans 

suggest that the resistance was mainly due to the use of fluoroquinolones in 

poultry.

Salmonella Bacteria Several epidemiologic studies using molecular subtyping have linked 

antibiotic-resistant salmonella infections in humans, another common 

foodborne illness, to animals. For example, in 1998 bacteria resistant to 

ceftriaxone were isolated from a 12-year-old boy who lived on a cattle farm 

in Nebraska.27 Molecular subtyping revealed that an isolate from the boy 

was indistinguishable from one of the isolates from the cattle on the farm. 

No additional ceftriaxone-resistant salmonella infections were reported in 

that state or adjoining states that could have been the cause of the 

infection. Similarly, an epidemiologic study in Poland from 1995 to 1997 

using molecular subtyping found identical profiles for ceftriaxone-resistant 

salmonella bacteria in isolates from poultry, feed, and humans.28 The 

researchers concluded that the salmonella infections were introduced in 

the poultry through the feed and reached humans through consumption of 

the poultry. Researchers in Taiwan also found that Salmonella enterica 

serotype choleraesuis bacteria that were resistant to ciprofloxacin in 

isolates collected from humans and swine were closely related and, 

following epidemiologic studies, concluded that the bacteria were 

transferred from swine to humans.29

27Paul D. Fey, Thomas J. Safranek, Mark E. Rupp, Eileen F. Dunne, Efrain Ribot, Peter C. 

Iwen, Patricia A. Bradford, Frederick J. Angulo, and Steven H. Hinrichs, “CeftriaxoneResistant Salmonella Infection Acquired by a Child from Cattle,” New England Journal of 

Medicine, vol. 342 (2000): 1242-1249.

28Andrzej Hoszowski and Dariusz Wasyl, “Typing of Salmonella enterica subsp. enterica

serovar Mbandaka Isolates,” Veterinary Microbiology, vol. 80 (2001): 139-148.

29Po-Ren Hsueh, Lee-Jene Teng, Sung-Pin Tseng, Chao-Fu Chang, Jen-Hsien Wan, Jing-Jou 

Yan, Chun-Ming Lee, Yin-Ching Chuang, Wen-Kuei Huang, Dine Yang, Jainn-Ming Shyr, 

Kwok-Woon Yu, Li-Shin Wang, Jang-Jih Lu, Wen-Chien Ko, Jiunn-Jong Wu, Feng-Yee Chang, 

Yi-Chueh Yang, Yeu-Jun Lau, Yung-Ching Liu, Cheng-Yi Liu, Shen-Wu Ho, and Kwen-Tay Luh, 

“Ciprofloxacin-Resistant Salmonella enterica Typhimurium and Choleraesuis from Pigs to 

Humans, Taiwan,” Emerging Infectious Diseases, vol. 10, no. 1 (2004): 60-68.
Page 22 GAO-04-490 Antibiotic Use in Animals

Researchers have also documented human infections caused by multidrugresistant strains of salmonella linked to animals. In 1982, researchers used 

molecular subtyping to show that human isolates of multidrug-resistant 

salmonella bacteria were often identical or nearly identical to isolates from 

animals.30 In the mid-1990s, NARMS data showed a rapid growth of 

multidrug resistance in Salmonella enterica serotype Typhimurium 

definitive type (DT) 104 among humans.31 Molecular subtyping found that 

human isolates with this strain of multidrug resistance in Salmonella 

enterica serotype Typhimurium DT104 in 1995 were indistinguishable from 

human isolates with this strain tested in 1985 and 1990. These results 

indicated that the widespread emergence of multidrug resistance in 

Salmonella enterica serotype Typhimurium DT104 may have been due to 

dissemination of a strain already present in the United States. Because food 

animals are the reservoir for most domestically acquired salmonella 

infections and transmission from animals to humans occurs through the 

food supply, the researchers concluded that the human infections were 

likely from the animals.

Recently, there has been an emergence of multidrug-resistant Salmonella 

enterica serotype Newport infections that include resistance to 

cephalosporins,32 such as cefoxitin.33 Based on molecular subtyping, 

multidrug-resistant salmonella isolates from cattle on dairy farms were 

found to be indistinguishable from human isolates. An epidemiologic study 

found that the infections in humans were associated with direct exposure 

30Thomas F. O’Brien, John D. Hopkins, Elaine S. Gilleece, Antone A. Medeiros, Ralph L. Kent, 

Billie O. Blackburn, Marion B. Holmes, Joseph P. Reardon, James M. Vergeront, Wendy L. 

Schell, Eleanor Christenson, Marjorie L. Bissett, and Erskine V. Morse, “Molecular 

Epidemiology of Antibiotic Resistance in Salmonella from Animals and Human Beings in the 

United States,” New England Journal of Medicine, vol. 307, no. 1 (1982): 1-6.

31Efrain M. Ribot, Rachel K. Wierzba, Frederick J. Angulo, and Timothy J. Barrett, 

“Salmonella enterica serotype Typhimurium DT104 Isolated from Humans, United States, 

1985, 1990, and 1995,” Emerging Infectious Diseases, vol. 8, no. 4 (2002): 387-391.

32Cephalosporins are antibiotics that are commonly used, especially in children, to treat 

severe salmonella infections.

33Amita Gupta, John Fontana, Colleen Crowe, Barbara Bolstorff, Alison Stout, Susan Van 

Duyne, Mike P. Hoekstra, Jean M. Whichard, Timothy J. Barrett, Frederick J. Angulo, for the 

National Antimicrobial Resistance Monitoring System PulseNet Working Group, 

“Emergence of Multidrug-Resistant Salmonella enterica Serotype Newport Infections 

Resistant to Expanded-Spectrum Cephalosporins in the United States,” Journal of 

Infectious Diseases, vol. 188 (2003): 1707-1716.
Page 23 GAO-04-490 Antibiotic Use in Animals

to a dairy farm, and the authors hypothesized that the infections were 

associated with handling or consuming the contaminated foods.

Many Studies Have Found 

That Transference of 

Antibiotic-Resistant 

Bacteria from Animals to 

Humans Is a Human Health 

Risk, but Researchers 

Disagree About the Extent 

of Risk

The extent of harm to human health from the transference of antibioticresistant bacteria from animals is uncertain. Many studies have found that 

the use of antibiotics in animals poses significant risks for human health, 

and some researchers contend that the potential risk of the transference is 

great for vulnerable populations. However, a small number of studies 

contend that the health risks of the transference are minimal.

Many Researchers Contend That 

Antibiotic Use in Animals Poses 

Significant Risk for Human 

Health 

Some studies have sought to determine the human health impacts of the 

transference of antibiotic resistance from animals to humans. For example, 

the Food and Agriculture Organization of the United Nations (FAO), OIE, 

and WHO recently released a joint report based on the scientific 

assessment of antibiotic use in animals and agriculture and the current and 

potential public health consequences.34 The report states that use of 

antibiotics in humans and animals alters the composition of microorganism 

populations in the intestinal tract, thereby placing individuals at increased 

risk for infections that would otherwise not have occurred. The report also 

states that use of antibiotics in humans and animals can also lead to 

increases in treatment failures and in the severity of infection.

Similarly, a recent review of studies regarding increased illnesses due to 

antibiotic-resistant bacteria found significant differences in treatment 

outcomes of patients with antibiotic-resistant bacterial infections and 

patients with antibiotic-susceptible bacterial infections.35 For example, one 

study found that hospitalization rates of patients with nontyphoidal 

salmonella infections were 35 percent for antibiotic-resistant infections 

and 27 percent for antibiotic-susceptible infections. That study also found 

34Food and Agriculture Organization of the United Nations, Office International des 

Epizooties, and World Health Organization, Joint FAO/OIE/WHO Expert Workshop on NonHuman Antimicrobial Usage and Antimicrobial Resistance: Scientific Assessment 

(Geneva, Switzerland, Dec. 1-5, 2003).

35Karin Travers and Michael Barza, “Morbidity of Infections Caused by AntimicrobialResistant Bacteria,” Clinical Infectious Diseases, vol. 34, suppl. 3 (2002): S131-S134.
Page 24 GAO-04-490 Antibiotic Use in Animals

that the length of illness was 10 days for antibiotic-resistant infections 

versus 8 days for antibiotic-susceptible infections. Another study found 

diarrhea from Campylobacter jejuni infections lasted 12 days for 

antibiotic-resistant infections versus 6 days for susceptible infections. Also, 

based on this review, the authors estimated that fluoroquinolone resistance 

likely acquired through animals leads to at least 400,000 more days of 

diarrhea in the United States per year than would occur if all infections 

were antibiotic-susceptible. The authors estimated that antibiotic 

resistance from nontyphoidal salmonella infections mainly arising from 

animals could account for about 8,700 additional days of hospitalization 

per year.

Experts are especially concerned about safeguarding the effectiveness of 

antibiotics such as vancomycin that are considered the “drugs of last 

resort” for many infections in humans. Evidence suggests that use of the 

antibiotic avoparcin in animals as a growth promoter may increase 

numbers of enterococci that are resistant to the similar antibiotic 

vancomycin. A particular concern is the possibility that vancomycinresistant enterococci could transfer resistance to other bacteria. Some 

Staphylococcus aureus infections found in hospitals are resistant to all 

antibiotics except vancomycin, and human health can be adversely 

affected, as treatment could be difficult, if not impossible, if these strains 

develop resistance to vancomycin, too. Recently, two human isolates of 

Staphylococcus aureus were found to be resistant to vancomycin.
Page 25 GAO-04-490 Antibiotic Use in Animals

With the increase in infections that are resistant to vancomycin, the 

streptogramin antibiotic quinupristin/dalfopristin (Q/D, also known as 

Synercid) has become an important therapeutic for life-threatening 

vancomycin-resistant enterococcus infections.36 Virginiamycin, which is 

similar to Q/D, has been used in animals since 1974, and Q/D was approved 

for human use in 1999. NARMS data from 1998 to 2000 indicate that Q/Dresistant Enterococcus faecium has been found in chicken and ground 

pork purchased in grocery stores, as well as in human stools.37 Experts 

hypothesize that use of virginiamycin in poultry production has led to Q/Dresistant bacteria in humans because the antibiotics are very similar, but 

the human health consequences of this have not been quantified.38

Experts are also concerned about risks to vulnerable populations such as 

individuals with compromised immune systems or chronic diseases, who 

are more susceptible to infections, including antibiotic-resistant infections. 

For example, salmonella infections are more likely to be severe, recurrent, 

or persistent in persons with human immunodeficiency virus (HIV). 

Another concern is that people with resistant bacteria could inadvertently 

spread those bacteria to hospitalized patients, including those with 

weakened immune systems.

36Vancomycin-resistant enterococcus infections are easily transmitted in health care settings 

and are difficult to treat.

37J. McClellan, K. Joyce, S. Rossiter, T. Barrett, F. J. Angulo, and the NARMS Enterococci 

Working Group, “High-Level Gentamicin Resistant Enterococci and 

Quinupristin/Dalfopristin Resistant E. faecium from Ground Pork Purchased from Grocery 

Stores” (paper presented at the 41st Interscience Conference on Antimicrobial Agents and 

Chemotherapy annual meeting, Chicago, Ill., 2001), and K. Gay, K. Joyce, J. Stevenson, F. 

Angulo, T. Barrett, and the NARMS Working Group, “Quinupristin/Dalfopristin-Resistant 

Enterococcus faecium Isolated from Human Stools, Retail Chicken, and Retail Pork: EIP 

Enterococci Project” (paper presented at the International Conference on Emerging 

Infectious Diseases, Atlanta, Ga., March 2002).

38Joshua R. Hayes, Angela C. McIntosh, Sadaf Qaiyumi, Judith A. Johnson, Linda L. English, 

Lewis E. Carr, David D. Wagner, and Sam W. Joseph, “High-Frequency Recovery of 

Quinupristin-Dalfopristin-Resistant Enterococcus faecium Isolates from the Poultry 

Production Environment,” Journal of Clinical Microbiology, vol. 39, no. 6 (2001): 2298-2299; 

and D. L. Smith, J. A. Johnson, A. D. Harris, J. P. Furuno, E. N. Perencevich, and J. G. Morris 

Jr., “Assessing Risks for a Pre-Emergent Pathogen: Virginiamycin Use and the Emergence of 

Streptogramin Resistance in Enterococcus faecium,” The Lancet Infectious Diseases, vol. 3 

(2003): 241-249.
Page 26 GAO-04-490 Antibiotic Use in Animals

Other Researchers Contend 

That Evidence of Human 

Health Risk from Antibiotic 

Use in Animals Is Lacking

Although it is generally agreed that transference is possible, some 

researchers contend that the health risks of the transference are minimal.39

Proponents of this view note that not all studies have shown an increase in 

antibiotic-resistant bacteria. For example, one study conducted between 

1997 and 2001 found no clear trend toward greater antibiotic resistance in 

salmonella bacteria.40

Proponents of this view also assert that restricting the use of antibiotics in 

animal agriculture could lead to greater levels of salmonella and 

campylobacter bacteria reaching humans through meat, thus increasing the 

risk of human infections. Conversely, some of these researchers also argue 

that the risk to humans of acquiring these infections from animals can be 

eliminated if meat is properly handled and cooked. They also cite a few 

studies that have concluded that the documented human health 

consequences are small. For example, they noted that one study estimated 

that banning the use of virginiamycin in animals in the U.S. would lower the 

number of human deaths by less than one over 5 years.41

39I. Phillips, M. Casewell, T. Cox, B. De Groot, C. Friis, R. Jones, C. Nightingale, R. Preston, 

and J. Waddell, “Does the Use of Antibiotics in Food Animals Pose a Risk to Human Health? 

A Critical Review of Published Data,” Journal of Antimicrobial Chemotherapy, vol. 53, no. 

1 (2004): 28-52.

40Jennifer M. Stephen, Mark A. Toleman, Timothy R. Walsh, Ronald N. Jones, and the 

SENTRY Program Participants Group, “Salmonella Bloodstream Infections: Report from the 

SENTRY Antimicrobial Surveillance Program (1997-2001),” International Journal of 

Antimicrobial Agents, vol. 22 (2003): 395-405.

41I. Phillips, M. Casewell, T. Cox, B. De Groot, C. Friis, R. Jones, C. Nightingale, R. Preston, 

and J. Waddell, “Does the Use of Antibiotics in Food Animals Pose a Risk to Human Health? 

A Critical Review of Published Data,” Journal of Antimicrobial Chemotherapy, vol. 53, no. 

1 (2004): 42.
Page 27 GAO-04-490 Antibiotic Use in Animals

Federal Agencies Have 

Increased Surveillance 

of Antibiotic 

Resistance from 

Animals to Assess 

Human Health Risk; 

Effectiveness of Risk 

Reduction Efforts Is 

Not Yet Known

FDA, CDC, and USDA have increased their surveillance activities related to 

antibiotic resistance in animals, humans, and retail meat since beginning 

these activities in 1996. New programs have been added, the number of 

bacteria being studied has increased, and the geographic coverage of the 

sampling has been expanded. In addition, all three agencies have 

sponsored research on the human health risk from antibiotic resistance in 

animals. FDA has taken several recent actions to minimize the human 

health risk of antibiotic resistance from animals, but the effectiveness of its 

actions is not yet known. These activities include administrative action to 

prohibit the use of the fluoroquinolone enrofloxacin (Baytril) for poultry 

and the development of a recommended framework for conducting 

qualitative risk assessments of all new and currently approved animal drug 

applications with respect to antibiotic resistance and human health risk. 

Federal Surveillance 

Activities for Antibiotic 

Resistance in Animals and 

Humans Have Increased

FDA, CDC, and USDA have six surveillance activities ongoing to identify 

and assess the prevalence of resistant bacteria in humans, animals, or retail 

meat. (See table 1.) Since 1996, these activities have expanded to include 

additional bacteria, greater geographic coverage, and new activities. Two of 

these activities—NARMS and Collaboration in Animal Health, Food Safety 

and Epidemiology (CAHFSE)—focus on antibiotic resistance from 

animals. The other four activities—Foodborne Diseases Active 

Surveillance Network (FoodNet), PulseNet, PulseVet, and National Animal 

Health Monitoring System (NAHMS)—focus on foodborne disease or 

animal health in general, not antibiotic resistance, but are nevertheless 

relevant to issues of antibiotic resistance. Figure 3 shows how these 

different surveillance activities provide data about various aspects of 

antibiotic resistance.
Page 28 GAO-04-490 Antibiotic Use in Animals

Table 1: Federal Surveillance Activities Related to Antibiotic Resistance and Foodborne Disease or Animal Health

Activity Purpose Lead agency Bacteria

Source of bacteria 

isolates

Focus on antibiotic resistance

National 

Antimicrobial 

Resistance 

Monitoring 

System—Enteric 

Bacteria 

(NARMS)

To monitor antimicrobial resistance among 

foodborne bacteria isolated from humans, animals, 

and retail foods and perform research to further 

evaluate resistance, including molecular analysis, 

and develop special projects to better understand 

resistance. Implement response activities to 

mitigate the resistance and perform epidemiologic 

studies. 

CDC (Human 

NARMS)

• Salmonella Typhi 

• non-Typhi 

Salmonella

• Campylobacter

• E. coli O157:H7

• Enterococcus

• Shigella

Humans 

USDA (Animal 

NARMS)

• Non-Typhi 

Salmonella

• Campylobacter

• generic E. coli

• Enterococcus

Animals: on farm, 

diagnostic, slaughter/ 

processing

FDA (Retail 

Meat NARMS)

• Non-Typhi 

Salmonella

• Campylobacter

• generic E. coli

• Enterococcus

Retail samples of 

ground beef, ground 

turkey, pork chops, 

chicken breastsa

Collaboration in 

Animal Health, 

Food Safety and 

Epidemiology 

(CAHFSE)

To assess the presence of bacteria, relate the 

onset and duration of infection with antibiotic use 

patterns in animals, and describe on-farm trends in 

the prevalence of bacteria.

USDA • Salmonella

• Campylobacter

• generic E. coli

• Enterococcus

Swine (on farm), 

expanding to include 

slaughter/processing

Focus on foodborne disease or animal health

Foodborne 

Diseases Active 

Surveillance 

Network 

(FoodNet)

To determine the incidence of foodborne diseases, 

monitor foodborne disease trends, and determine 

the proportion of foodborne diseases attributable to 

specific foods and settings. 

CDC • Salmonella

• Campylobacter

• Shigatoxin-producing 

E. coli (e.g., E. coli

O157:H7)

• Shigella

• Listeria

• Vibrio

• Yersinia

• Cryptosporidium

• Cyclospora

Humans 

PulseNet To provide data on the extent and relatedness of 

outbreaks and individual isolates of foodborne 

disease.

CDC • Non-Typhi 

Salmonella

• E. coli O157:H7

• Listeria

• Shigella

• Campylobacter

Humans and foodb

PulseVet To conduct DNA fingerprinting of animal bacteria. USDA • Salmonella Animals from 

slaughter/processing
Page 29 GAO-04-490 Antibiotic Use in Animals

Source: GAO.

a

The retail meat program of NARMS, with USDA, will also look at susceptibilities of 

recovered E. coli and salmonella bacteria obtained from their produce surveys.

b

PulseNet includes any type of food, not just retail meat.

Figure 3: Sources of Data from Surveillance Activities about Antibiotic Resistance and Foodborne Disease or Animal Health

Note: CAHFSE = Collaboration in Animal Health, Food Safety and Epidemiology; 

NARMS = National Antimicrobial Resistance Monitoring System—Enteric Bacteria; 

NAHMS = National Animal Health Monitoring System; FoodNet = Foodborne Diseases Active 

Surveillance Network.

National Animal 

Health 

Monitoring 

System 

(NAHMS)

To collect, analyze, and disseminate data on 

animal health, management, and productivity.

USDA • Salmonella Animals on farm

(Continued From Previous Page)

Activity Purpose Lead agency Bacteria

Source of bacteria 

isolates

CAHFSE

Animals Humans Retail Meat

Source: GAO. 

NARMS

NAHMS PulseVet FoodNet PulseNet

Analyze samples from animals

Analyze samples from humans

Analyze samples from retail meat

Focus on foodborne disease

Focus on antibiotic resistance
Page 30 GAO-04-490 Antibiotic Use in Animals

NARMS and CAHFSE Focus on 

Antibiotic Resistance

NARMS monitors changes in susceptibilities of bacteria in humans and 

animals to antibiotics. To assess the extent of changes in levels of 

resistance, NARMS collects animal and human isolates of six different 

bacteria, specifically non-Typhi Salmonella, Campylobacter, E. coli,

Enterococcus, Salmonella Typhi, and Shigella.42 These activities are 

conducted under three independent, yet coordinated, programs, with FDA 

serving as the funding and coordinating agency. The human program 

gathers isolates from humans and is led by CDC. The animal program, led 

by USDA, gathers isolates from animals on farms, from slaughter and 

processing plants, and from diagnostic laboratories. The retail meat 

program gathers samples of meat purchased at grocery stores and is run by 

FDA. The agencies work together to standardize results through ongoing 

quality control efforts.

NARMS has expanded in three major ways—range of bacteria tested, 

geographic coverage, and number of programs—since it was established in 

1996. For example, human NARMS started by looking at two bacteria and 

now studies six bacteria.43 Further, NARMS also assessed the potential of 

other bacteria to become sources of resistance by collecting and assessing 

listeria and vibrio isolates in pilot studies.44 With regard to geographic 

coverage, the number of participating health departments has increased 

from 14 state and local health departments in 1996 to all 50 states and 

Washington, D.C., in 2003.45 Finally, the retail meat program was added in 

2002. Initially, 5 states participated in the retail meat program, but by 2004, 

10 states were participating. Despite this recent expansion, all of NARMS 

experienced budget cuts in fiscal year 2004, calling into question future 

expansion efforts. For example, the USDA budget for the animal program 

was cut 17.6 percent for 2004.

42Two of the bacteria studied in NARMS—Salmonella Typhi and Shigella—do not occur in 

food animals but are acquired by humans as a result of poor hygiene. As a result, they are 

not tested in the animal or retail meat programs of NARMS.

43NARMS began testing human non-Typhi salmonella and E. coli O157:H7 isolates. As of 

early 2004, NARMS tests Salmonella Typhi, non-Typhi salmonella, E. coli, campylobacter, 

enterococcus, and shigella isolates.

44Because little antibiotic resistance was found in these isolates, these bacteria are no longer 

tested for antibiotic susceptibility. 

45In 1999, testing of campylobacter isolates was limited to seven of these departments. By 

2003, 10 states were participating in campylobacter testing. 
Page 31 GAO-04-490 Antibiotic Use in Animals

NARMS has also produced collaborative research efforts among FDA, 

CDC, and USDA and helped further scientific understanding of antibiotic 

resistance. For example, data from NARMS led CDC to conclude that the 

proportion of campylobacter isolates resistant to ciprofloxacin in 2001 was 

2.4 times higher than in 1997.46 Similarly, FDA and CDC officials reported 

that NARMS data were used to evaluate antibiotic resistance to 

fluoroquinolones, and CDC officials told us that after NARMS data showed 

an increased number of cases of Salmonella Newport infections in humans, 

researchers at CDC and USDA shared human and animal isolates to 

determine whether the same pattern existed in animals.

CAHFSE, established by USDA in 2003, collects samples from animals on 

farms to identify changes in antimicrobial resistance over time. The first 

animals that are being tested in the program are swine. USDA conducts 

quarterly sampling of 40 fecal and 60 blood samples from animals from 

farms in four states. As of March 2004, 40 farms were participating in 

CAHFSE. In addition to the laboratory analyses, there are plans for risk 

analyses, epidemiologic studies, and field investigations, as well as analysis 

of samples collected at slaughter, and the addition of more species, funding 

permitted. 

Other Activities Focus on 

Foodborne Disease or Animal 

Health

FoodNet, PulseNet, PulseVet, and NAHMS focus on foodborne disease or 

animal health rather than antibiotic resistance. FoodNet, the principal 

foodborne disease component of CDC’s Emerging Infections Program, is a 

collaborative project with 10 states (referred to as FoodNet sites), USDA, 

and FDA.47 The goals of FoodNet are to determine the incidence of 

foodborne diseases, monitor foodborne disease trends, and determine the 

proportion of foodborne diseases attributable to specific foods and 

settings. FoodNet data are derived from specimens collected from patients. 

Isolates from these specimens are sent to NARMS for susceptibility testing. 

CDC officials reported that one of every 20 patients with a specimen in 

FoodNet also has an isolate in NARMS. 

A recent development has been the linking of the NARMS and FoodNet 

data systems. For example, FoodNet data can be used to determine 

46CDC, National Antimicrobial Resistance Monitoring System for Enteric Bacteria 

(NARMS): 2001 Annual Report, Atlanta, Ga: HHS, CDC, 2003.

47CDC officials reported that USDA and FDA provide one-third of the funding for FoodNet, 

and the agencies and states each have representatives on FoodNet’s steering committee.
Page 32 GAO-04-490 Antibiotic Use in Animals

whether an individual was hospitalized, and NARMS data can reveal 

whether the bacteria that infected the person were resistant to antibiotics. 

CDC officials reported that because of the linked databases, they were able 

to determine whether, for example, someone with an antibiotic-resistant 

salmonella infection was more likely to be hospitalized than someone with 

an antibiotic-susceptible salmonella infection. FoodNet also has a role in 

the retail meat program of NARMS. The FoodNet sites purchase the meat 

samples from grocery stores, examine the samples for the prevalence or 

frequency of bacterial contamination, and forward isolates of the bacteria 

to FDA for susceptibility testing for antibiotic resistance.

PulseNet is CDC’s early warning system for outbreaks of foodborne 

disease. USDA recently established a similar animal program, called 

PulseVet. PulseNet studies isolates from humans and suspected food, and 

PulseVet studies isolates from animals.48 Both PulseNet and PulseVet 

conduct DNA fingerprinting of bacteria49 and compare those patterns to 

other samples in order to identify related strains. The PulseNet and 

PulseVet isolates are tested for antibiotic resistance at CDC and USDA, 

respectively. FDA also performs DNA fingerprinting on salmonella and 

campylobacter isolates obtained from the retail meat program of NARMS 

and submits these data to PulseNet. 

NAHMS, which focuses on healthy animals, was initiated by USDA in 1983 

to collect, analyze, and disseminate data on animal health, management, 

and productivity across the United States. Since 1990, USDA has annually 

conducted studies on animal health, including information about antibiotic 

use, through NAHMS. Each study focuses on different animals, including 

swine, cattle (both dairy and beef), and sheep. NAHMS provides only a 

snapshot of a particular species or commodity; it does not track changes 

over time. While NAHMS contributes information about healthy animals, a 

USDA official told us that it also includes information about antibiotics 

used and may include information on the route of administration and the 

reason for treatment, which can be useful in further understanding NARMS 

findings. In addition, researchers and veterinarians are able to access the 

NAHMS database for studies of disease incidence, risk assessment, and 

48PulseNet fingerprints salmonella, E. coli, listeria, and shigella isolates, and PulseVet 

fingerprints salmonella and plans to include, as funding allows, campylobacter, 

enterococcus, and generic E. coli isolates.

49DNA fingerprinting is performed through genetic relatedness studies using pulsed-field gel 

electrophoresis.
Page 33 GAO-04-490 Antibiotic Use in Animals

preventive treatment techniques. Further, bacteria samples obtained from 

NAHMS have been added to the NARMS database. 

Federally Funded Research 

Is Under Way to Study the 

Human Health Risk of 

Antibiotic Resistance in 

Food Animals

Under the federal Interagency Task Force on Antimicrobial Resistance 

action plan, FDA, CDC, and USDA have initiated a number of research 

efforts that are relevant to antibiotic use in animals and human health. 

These ongoing research efforts focus on defining the effects of using 

various animal drugs on the emergence of antibiotic-resistant bacteria and 

identifying risk factors and preventive measures. Through CDC, FDA 

currently has cooperative agreements with four veterinary schools to study 

ways to reduce antibiotic-resistant bacteria in animals and is assessing the 

prevalence of antibiotic-resistant DNA in feed ingredients.50 In addition, 

FDA annually issues a 3-year research plan that describes research 

focusing on, among other things, antibiotic resistance in animals and its 

consequences for human health. Current studies include efforts to examine 

the consequences of antibiotic use in animals, the transmission of 

antibiotic resistance, and the processes underlying the spread of antibiotic 

resistance. In total, CDC has funded three projects under its Antimicrobial 

Resistance Applied Research extramural grant program. One of these 

grants, for example, is to study the prevalence of antibiotic-resistant E. coli

in chicken and ground beef products, examine the risk factors for human 

colonization with a resistant strain of E. coli, and compare characteristics 

of antibiotic-susceptible and antibiotic-resistant isolates from meat with 

those of antibiotic-susceptible and antibiotic-resistant isolates from 

humans. Similarly, USDA has funded studies of antibiotic resistance in 

chicken, turkey, pork, and dairy products. These studies have provided 

additional sources of isolates to FDA for risk assessment purposes. Also, 

USDA’s Cooperative State Research, Education, and Extension Service has 

funded over 30 studies related to antibiotic resistance since 2000 and 

awarded an additional $8 million in grants in 1999 and 2000. Funded 

research includes studies on the prevalence, development, and possible 

transmission of antibiotic resistance; the epidemiology of antibiotic 

resistance; and the evaluation of management practices and potential 

prevention/intervention strategies for antibiotic resistance.

50Animal feeds may include animal products or parts which have DNA. For example, cattle 

feed, may include blood and blood products, among others. See 21 C.F.R. §§ 

589.2000(a)(1),(7),(b)(2003).
Page 34 GAO-04-490 Antibiotic Use in Animals

FDA Has Taken Action to 

Minimize the Potential 

Human Health Risk of 

Antibiotic Resistance from 

Animals, but It Is Too Early 

to Determine Effectiveness 

FDA has taken a variety of actions to minimize the risk to the public health 

of antibiotic resistance in humans resulting from the use of antibiotics in 

animals, although it is still too early to determine the effectiveness of these 

actions. First, FDA has taken action to prohibit the use of an already 

approved animal drug for poultry because of concerns about human health 

risk. Second, the agency developed a recommended framework for 

reviewing all new animal antibiotic applications with respect to antibiotic 

resistance and human health risk. Third, FDA has begun reviewing 

antibiotics currently approved for use in animals according to its new 

framework to determine whether FDA needs to act to ensure that the drugs 

are safe. It is too early to determine the effectiveness of FDA’s review of 

currently marketed drugs. FDA has not made drugs used in animals that are 

critically important for human health its top priority for review, and any 

remedial actions pursued by the agency may take years to complete.

FDA Has Initiated Action to 

Prohibit the Use of Enrofloxacin 

in Poultry, but Proceedings Not 

Yet Complete 

On October 31, 2000, FDA proposed withdrawing the approval of 

enrofloxacin (Baytril), a fluoroquinolone drug used in poultry,51 after 

human health risks associated with the use of the drug in chickens and 

turkeys were documented by, among others, NARMS. Enrofloxacin is 

administered to flocks of poultry in their water supply to control mortality 

associated with E. coli and Pasteurella multocida organisms. FDA had 

found that new evidence, when evaluated with information available when 

the application was approved, demonstrated that enrofloxacin used with 

poultry flocks has not been shown to be safe for humans. Specifically, FDA 

determined that the use of enrofloxacin in poultry causes the development 

of a fluoroquinolone-resistant strain of campylobacter in poultry, which, 

when transferred to humans, is a significant cause of fluoroquinoloneresistant campylobacter infections in humans.

Before proceeding with formal efforts to withdraw approval for use of 

enrofloxacin with poultry flocks, FDA considered a number of alternative 

actions. For example, the agency determined that changing the label to 

limit use to the treatment of individual birds and limiting use to one time or 

one treatment per individual bird were impractical. The agency also 

considered and rejected the establishment of a registry that would require 

veterinarians to demonstrate the need for the drug. FDA proceeded with its 

efforts to withdraw approval of enrofloxacin for use in poultry because 

5165 Fed. Reg. 64954 (Oct. 31, 2000). There were two fluoroquinolones approved at that time: 

sarafloxacin hydrochloride and enrofloxacin.
Page 35 GAO-04-490 Antibiotic Use in Animals

FDA knew that there were alternative effective drugs for treating these 

illnesses in poultry.

In February 2002, FDA announced that a hearing would be held on the 

proposal to withdraw approval of enrofloxacin.52 Since FDA’s proposed 

action to ban the use of enrofloxacin in poultry, representatives of both 

FDA and Bayer, the manufacturer of Baytril, as well as numerous experts, 

have provided testimony on the question of its safety. Submission of 

written testimony was due in December 2002, and cross-examination of 

witnesses took place from late April 2003 through early May 2003. The final 

posthearing briefs and responses were delivered in July and August 2003. 

On March 16, 2004, an FDA administrative law judge issued an initial 

decision withdrawing the approval of the new animal drug application for 

Baytril. This decision will become final unless it is appealed to the FDA 

Commissioner by Bayer or another participant in the case or the 

Commissioner chooses to review it on his own initiative.53 If the 

Commissioner reviews and upholds the initial decision, Bayer or another 

participant may choose to appeal in court.54

Effectiveness of FDA’s 

Framework for Reviewing New 

Animal Drugs Is Not Yet Known 

FDA has determined that the human health risk from antibiotic use in 

animals is not acceptable, and the agency may initiate risk management 

strategies to contain such risk. In October 2003, as part of its efforts to 

approve and regulate animal drugs, FDA issued Guidance for Industry #152. 

The guidance outlines a framework for determining the likelihood that an 

antibiotic used to treat an animal would cause an antibiotic resistance 

problem in humans who consume meat or other food products from 

animals. The guidance’s risk assessment framework is based on three 

factors—the probability that resistant bacteria are present in the target 

animal, the probability that humans would ingest the bacteria in question 

from the relevant food commodity, and the probability that human 

exposure to resistant bacteria would result in an adverse health 

consequence. The resulting overall risk estimate is ranked as high, medium, 

or low. 

52After the original notice of FDA’s plans to withdraw approval of enrofloxacin for poultry, 

the only other manufacturer of an approved fluoroquinolone for poultry, Abbott 

Laboratories, voluntarily requested withdrawal of the approval for its drug sarafloxacin 

hydrochloride (SaraFlox).

53The only other participant in the case is the Animal Health Institute.

54See 21 C.F.R. §§ 12.120-12.140(2003).
Page 36 GAO-04-490 Antibiotic Use in Animals

Because the guidance is new, it is not yet known how the results of a risk 

assessment conducted according to the guidance will influence FDA’s 

decisions to approve new drug applications. Agency officials told us that 

FDA has never denied a new or supplemental animal drug application 

because of evidence that the drug caused antibiotic resistance in humans. 

In addition, the risk assessment guidance states that drugs with high risk 

may still be approved, though with specific use restrictions, if there is a 

reasonable certainty of no harm to human health when the drug is 

approved. These restrictions might include availability only by 

prescription, restrictions on uses not specified on the label (known as 

extralabel use), limitations for use in individual animals (versus groups of 

animals) for fewer than 21 days, and requirements for postapproval 

monitoring. FDA has previously used these kinds of restrictions with some 

drugs. While agency officials told us that the extralabel use prohibitions for 

animal drugs have generally reduced unauthorized use, such use 

restrictions may not prevent human health risk. For example, while FDA 

had earlier limited fluoroquinolones to use by or under the order of a 

veterinarian and prohibited the extralabel use of fluoroquinolones, the 

agency has now concluded that a human health risk exists despite these 

restrictive measures.

FDA officials reported that the agency has reviewed about seven new drug 

applications using the risk assessment framework in Guidance for Industry 

#152. Some of those drugs have been approved. Other drugs have been 

approved but with label claims different from those requested in the 

application. FDA officials have not denied approval to any of these new 

drug applications. 
Page 37 GAO-04-490 Antibiotic Use in Animals

Timing and Effectiveness of FDA 

Plans to Review Currently 

Marketed Animal Antibiotics for 

Human Health Risk Are 

Uncertain

To determine whether future regulatory actions may be necessary, FDA is 

conducting risk assessments for drugs currently used in animal agriculture 

that are also important for human medicine. FDA began with two 

quantitative risk assessments for drugs ranked as critically important for 

human health at the time the assessments were initiated. FDA completed 

the assessment for fluoroquinolones in October 2000 and expects to 

complete the assessment for virginiamycin, a streptogramin drug related to 

Synercid, its counterpart for humans, in 2004.55 The quantitative risk 

assessments calculate estimates of the number of cases of infection. 

Agency officials told us that they had hoped that the quantitative risk 

assessment approach would provide a template for future risk 

assessments. However, FDA decided that it did not. 

FDA officials told us that as a result, the agency plans to review other 

currently marketed antibiotics using the qualitative risk assessment 

framework outlined in Guidance for Industry #152, which uses broad 

categories to assess risk. An FDA official reported that if the information 

necessary to complete any section of the qualitative risk assessment were 

unavailable, the agency would assign a higher score to the product, to err 

on the side of caution. After outlining possible risk management steps, if 

any, the agency would allow a drug’s sponsor (generally pharmaceutical 

firms) to provide additional information to help FDA reconsider its risk 

estimate. Generally, these qualitative risk assessments are considered to be 

a starting point for examining human health risk for some drugs. 

55Virginiamycin is no longer considered a critically important drug. Synercid, was the first 

antibiotic approved for the treatment of vancomycin-resistant Enterococcus faecium

bacteremia and was the only drug available for treatment when the risk assessment began. 

Since that time, other drugs have been developed, and the status of virginiamycin has been 

reduced from critically important to highly important for human health.
Page 38 GAO-04-490 Antibiotic Use in Animals

FDA has not made drugs that are critically important for human health its 

top priority for review.56 (See app. III for more detail on evaluating the 

importance of an animal drug for human health.) Instead, the agency

focused its first qualitative risk assessments on subtherapeutic penicillin 

and tetracycline drugs.57 These assessments are expected to be completed 

by April 2004. FDA officials told us that the agency will then conduct 

qualitative risk assessments for therapeutic penicillin and tetracycline 

drugs, followed by assessments for those drugs that are defined in 

Guidance for Industry #152 as critically important for human health. As of 

March 2004, there were four such categories of drugs.58 

For a number of reasons, it is not known whether FDA’s new framework for 

reviewing currently approved and marketed animal drugs will be able to 

effectively identify and reduce any human health risk. First, under this 

plan, it may take years for FDA to identify and reduce any human risk of 

acquiring antibiotic resistance from meat. FDA has not developed a 

schedule for conducting the qualitative risk assessments on the currently 

approved drugs, and the assessments may take a significant amount of time 

to complete. For example, based on the current schedule, FDA officials 

told us they expect the qualitative risk assessment of subtherapeutic 

penicillins and tetracyclines, which were begun in 2002, to take nearly 2 

years to complete. Second, FDA officials told us that the risk estimation 

from the qualitative risk assessments will only use data already available in 

the original new drug application and any supplemental drug applications, 

rather than actively seeking new evidence. However, FDA told us that new 

evidence was an important factor in its risk assessment of 

fluoroquinolones. Finally, while FDA can pursue a number of enforcement 

options if its reviews uncover a human health risk, it is not known if they 

will be effective or how long it will take for such changes to take effect. As 

the enrofloxacin case demonstrates, risk management strategies may not 

mitigate human health risk, and administrative proceedings can extend for

56FDA has rated classes of animal drugs as critically important, highly important, or 

important to human health.

57Subtherapeutic drugs are typically used to enhance growth rates or improve feed 

efficiency. 

58Categories of drugs identified in Guidance for Industry #152 as critically important for 

human health include third-generation cephalosporins, fluoroquinolones, macrolides, and 

trimethoprim/sulfamethoxazole.
Page 39 GAO-04-490 Antibiotic Use in Animals

several years after FDA decides to take enforcement action.59 An FDA 

official also told us that if the drug sponsor voluntarily cooperates in 

implementing risk management strategies, lengthy administrative 

proceedings may be avoided.

Federal Agencies Do 

Not Collect Data 

Needed to Address the 

Risk of Antibiotic 

Resistance Associated 

with Use in Animals

Although they have made some progress in monitoring antibiotic resistance 

associated with antibiotic use in animals, federal agencies do not collect 

data on antibiotic use in animals that are critical to supporting research on 

the human health risk. Data on antibiotic use would allow agencies to link 

use to the emergence of antibiotic-resistant bacteria, help assess the risk to 

human health, and develop strategies to mitigate resistance. FDA and 

USDA do not collect these data because of costs to the industry and other 

factors. Countries that collect antibiotic use data, depending on the amount 

and type of data collected, have been able to conduct more extensive 

research than U.S. agencies. 

Federal Agencies Do Not 

Collect Needed Data

According to FDA, CDC, and USDA, more data are needed on antibiotic use 

in animals in order to conduct further research on antibiotic resistance 

associated with this use. In particular, FDA has stated that it needs 

information on the total quantity of antibiotics used in animals, by class; 

the species they are used in; the purpose of the use, such as disease 

treatment or growth promotion; and the method used to administer the 

antibiotic. WHO and OIE have also recommended that countries collect 

such data. This information could be used for the following:

• To link antibiotic use to emerging strains of antibiotic-resistant 

bacteria. Antibiotic use information would clarify the relationship 

between resistance trends in NARMS and the actual use of antibiotics. 

For example, detailed on-farm data on antibiotic use and other 

production practices that are linked to bacteria samples from animals 

could help identify the conditions under which resistant bacteria 

develop. 

59By law, the Secretary of HHS can also determine that there is an imminent hazard from an 

animal drug. In such cases, the authority to market the drug could be immediately 

suspended pending challenges from the manufacturer. 21 U.S.C. §360b(e)(2000).
Page 40 GAO-04-490 Antibiotic Use in Animals

• To help assess risk to human health. Information on antibiotic use 

would help assess the likelihood that humans could be exposed to 

antibiotic-resistant bacteria from animals. This potential exposure is 

important in determining the risk that antibiotic use in animals may 

pose to human health. 

• To develop and evaluate strategies to mitigate resistance. Data on 

antibiotic use would help researchers develop strategies for mitigating 

increased levels of resistant bacteria in animals, according to CDC 

officials. Strategies could be developed based on such factors as the way 

the drug is administered, dosage levels, or use in a particular species. In 

addition, unless data are available for monitoring the effects of these 

interventions, researchers cannot assess the strategies’ effectiveness.

FDA recognizes that additional data on antibiotic use in animal production 

would facilitate research on the linkages to human resistance. To that end, 

FDA had considered a plan that would have required pharmaceutical 

companies to provide more detailed information on antibiotics distributed 

for use in animals.60 This information would have been reported as a part of 

FDA’s ongoing monitoring of these antibiotics after their approval. 

However, according to FDA officials, this more detailed reporting would 

have resulted in significant costs to the pharmaceutical industry.61

Consequently, FDA is analyzing other options to minimize the burden to the 

industry. 

In addition, the information that USDA collects through NAHMS is of 

limited use for supporting research on the relationship between antibiotic 

use in animals and emerging antibiotic-resistant bacteria. NAHMS was not 

designed to collect antibiotic use data; instead, as previously discussed, its 

main goal is to provide information on U.S. animal health, management, 

and productivity. Through NAHMS, USDA does collect some data on 

60In addition, the Animal Health Institute—a trade association representing veterinary 

pharmaceutical manufacturers—publishes yearly information on the total quantity of 

animal antibiotics sold by its members. The Animal Health Institute’s members account for 

about 85 percent of animal drug sales in the United States. Its reports present the data by 

antibiotic class and groups certain classes together. The data include amounts sold for both 

livestock and pets and are not separated by species. 

61According to Animal Health Institute officials, many manufacturers sell antibiotics to 

wholesale distributors or feed mills and cannot provide the details on the end use of their 

products. In addition, certain antibiotics are authorized for use in multiple species and for 

multiple purposes. 
Page 41 GAO-04-490 Antibiotic Use in Animals

antibiotic use, but only periodically and only for certain species. For 

example, it has studied the swine industry every 5 years since 1990 but has 

not yet studied broiler chickens—the most common type of poultry 

Americans consume. 

USDA’s Collaboration in Animal Health, Food Safety and Epidemiology 

(CAHFSE) is a new program designed to enhance understanding of 

bacteria that pose a food safety risk. USDA plans to monitor, over time, the 

prevalence of foodborne and other bacteria, as well as their resistance to 

antibiotics on farms and in processing plants. These data are expected to 

facilitate research on the link between agricultural practices, such as the 

use of antibiotics, and emerging resistant bacteria. Currently, however, 

CAHFSE does not provide information on the impact of antibiotic use for 

species such as poultry and cattle and for a significant portion of the swine 

industry. According to USDA, CAHFSE funding comes primarily from a 

limited amount of funding that is redirected from other USDA programs, 

and the program would need additional funding before it could expand to 

cover processing plants, more swine operations, or other species. USDA 

officials told us they plan to coordinate data collection and analysis efforts 

for CAHFSE with NARMS activities at FDA and CDC. 

According to the officials we spoke with at market research firms, private 

companies also collect some data on antibiotic use, but this information is 

developed for commercial purposes and is not always available for public 

research. These companies collect information on animal production 

practices, including antibiotic use, and sell this information to producers, 

who use it to compare their production costs and practices with those of 

other producers. They also sell these data to pharmaceutical companies, 

which use the information to estimate the future demand for their 

products. In any case, the market research firms do not design their data 

collection efforts to assist research on antibiotic resistance. 

Other Countries Collect 

Data That Are Useful for 

Conducting Research on 

Antibiotic Use and 

Developing Strategies to 

Mitigate Antibiotic 

Resistance

Unlike the United States, other countries, such as Denmark, New Zealand, 

and the United Kingdom, collect more extensive data on antibiotic use in 

animals. Among the countries we examined, Denmark collects the most 

comprehensive and detailed data, including information on the quantities 

of antibiotics used in different animal species by age group and method of 

administration. According to Danish researchers, these data have allowed 

them to take the following actions:
Page 42 GAO-04-490 Antibiotic Use in Animals

• Link antibiotic use in animals to emerging strains of antibioticresistant bacteria. Danish researchers have been able to determine how 

changes in the consumption of antibiotics in animals affect the 

occurrence of antibiotic-resistant bacteria. In addition, researchers 

began collecting additional data on antibiotic-resistant bacteria in 

humans in 2002, allowing them to explore the relationship between 

levels of antibiotic-resistant bacteria in animals, food, and humans.

• Develop strategies to mitigate resistance. By monitoring trends in 

antibiotic use and levels of antibiotic-resistant bacteria, Denmark has 

been able to adjust national veterinary use guidelines and revised 

regulations to minimize potential risk to human health. 

Other countries, such as New Zealand and the United Kingdom, have data 

collection systems that are not as comprehensive as Denmark’s. 

Nevertheless, these nations collect data on total sales for antibiotics used 

in animals by class of antibiotic. The United Kingdom is also working to 

more accurately track the sales of antibiotics for use in different species. 

These data show trends in use over time and identify the importance of 

different antibiotic classes for the production of livestock and poultry. 

According to the official responsible for the United Kingdom’s data 

collection system, collecting these data requires few resources. In addition, 

Canadian officials told us Canada is collecting some data on antibiotic use 

on farms and expects to collect data on sales of antibiotics used in animals. 

Canada also plans to develop comprehensive methods to collect use data 

and integrate these data into its antibiotic resistance surveillance system. 

According to Canada’s first annual report on antibiotic resistance, issued in 

March 2004, its next annual report will include some information on 

antibiotic use in animals. See appendix IV for information on other 

countries’ data collection systems. 
Page 43 GAO-04-490 Antibiotic Use in Animals

The United States and 

Its Key Trading 

Partners and 

Competitors Differ in 

the Restrictions They 

Place on the Use of 

Antibiotics in Animals

The United States and several of its key trading partners, such as Canada 

and South Korea, and its competitors, such as the EU, differ in their use of 

antibiotics in animals in two important areas: the specific antibiotics that 

can be used for growth promotion and the availability of antibiotics to 

producers (by prescription or over the counter).62

With respect to growth promotion in animals, the United States, as well as 

Australia, Canada, Japan, and South Korea, allow the use of some 

antibiotics from classes important in human medicine.63 However, the 

United States and Australia are currently conducting risk assessments to 

determine whether to continue to allow the use of some of these antibiotics 

for growth promotion. Canada plans to conduct similar risk assessments, 

and Japan is reviewing the use of antibiotics for growth promotion if those 

antibiotics are from classes used in humans. In contrast, New Zealand has 

completed its risk assessments of antibiotics used for growth promotion 

and no longer allows the use of any antibiotics for growth promotion that 

are also related to antibiotics used in human medicine. Similarly, the EU 

has prohibited its member countries from using antibiotics in feed for 

growth promotion if those antibiotics are from antibiotic classes used in 

human medicine. In addition, the EU has issued a regulation that will 

prohibit the use of all other antibiotics in feed for growth promotion by 

2006.64 

We found differences among the United States’ and other countries’ use of 

antibiotics for growth promotion in the following four antibiotic classes 

that FDA has ranked as critically or highly important in human medicine:

• Macrolides. The United States, Canada, and South Korea allow 

antibiotics from the macrolide class for growth promotion, but the EU 

62With regard to trade in meat, the key U.S. trading partners on which we obtained 

information were the EU, Australia, Canada, China, Denmark, Hong Kong, Japan, Mexico, 

New Zealand, Russia, and South Korea; the key U.S. competitors were the EU, Australia, 

Brazil, Canada, and Denmark. We did not independently verify the information in foreign 

government documents, which included laws and regulations. 

63China, Hong Kong, and Mexico allow the use of antibiotics for growth promotion. We did 

not obtain information on whether these include antibiotics from classes important in 

human medicine.

64The EU will still allow the use of coccidiostat and histomonostat drugs as feed additives 

for growth promotion. These drugs control parasites, and many coccidiostat and 

histomonostat drugs are not used in humans.
Page 44 GAO-04-490 Antibiotic Use in Animals

and New Zealand do not.65 In the United States, tylosin, a member of this 

class, is among the most commonly used antibiotics for growth 

promotion in swine. As of March 2003, Australia allowed antibiotics 

from the macrolide class for growth promotion, but it had a review 

under way on some antibiotics in this class, including tylosin, to 

determine if growth promotion use should continue.

• Penicillins and tetracyclines. The United States, Canada, and South 

Korea allow certain antibiotics from these two classes to be used for 

growth promotion, but Australia, the EU, Japan, and New Zealand do 

not. Furthermore, as mentioned earlier, the United States is currently 

conducting risk assessments on these two classes to determine whether 

to continue allowing their use for growth promotion. 

• Streptogramins. The United States, Canada, and South Korea allow the 

use of virginiamycin, an antibiotic from this class, for growth promotion, 

but the EU and New Zealand do not. The United States is conducting a 

risk assessment on the use of virginiamycin for growth promotion and 

disease prevention. As of April 2003, Australia permitted virginiamycin 

for growth promotion, but the Australian agency that regulates 

antibiotic use in animals has recommended that approval of this use be 

withdrawn. 

Appendix V lists antibiotics—including antibiotics from the above 

classes—that are frequently used in U.S. animal production.

With regard to the availability of antibiotics to livestock and poultry 

producers, public health experts advocate requiring a veterinarian’s 

prescription for the sale of antibiotics. They believe that this requirement 

may help reduce inappropriate antibiotic use that could contribute to the 

emergence of antibiotic-resistant bacteria in animals and the human health 

risk associated with these resistant bacteria. 

The United States and Canada permit many antibiotics to be sold over the 

counter, without a veterinarian’s prescription, while the EU countries and 

New Zealand are more restrictive regarding over-the-counter sales.66 The 

65The United States has not started a risk assessment for any antibiotic in this class.

66Australia, Brazil, China, Hong Kong, Japan, Mexico, Russia, and South Korea permit the 

sale of some antibiotics over the counter. We did not obtain more detailed information on 

which antibiotics these countries allow to be sold in this manner. 
Page 45 GAO-04-490 Antibiotic Use in Animals

United States and Canada generally allow older antibiotics, such as 

sulfamethazine, to be sold over the counter, but they require a prescription 

for newer antibiotics, such as fluoroquinolones. In addition, with regard to 

the availability of antibiotics from antibiotic classes that are important in 

human medicine, the United States and Canada allow livestock and poultry 

producers to purchase several antibiotics over the counter, including 

penicillins, tetracyclines, tylosin, and virginiamycin. However, Canada is 

considering changing its rules to require prescriptions for antibiotics used 

in animals for all antibiotic uses except growth promotion. 

In contrast, the EU countries and New Zealand are more restrictive 

regarding over-the-counter sales of antibiotics for use in animals. Unlike 

the United States and Canada, the EU does not allow penicillins, 

tetracyclines, tylosin, and virginiamycin to be sold over the counter and 

will end all over-the-counter sales by 2006. Denmark, an EU member, 

already prohibits all over-the-counter sales. Similarly, New Zealand requires 

producers to have a veterinarian’s prescription for antibiotics that it has 

determined are associated with the development of resistant bacteria in 

humans.

Appendix IV contains additional information on the key U.S. trading 

partners and competitors discussed in this section, including, as previously 

mentioned, their systems for collecting data on antibiotic use.

Antibiotic Use in 

Animals Has Not 

Significantly Affected 

U.S. Trade but Could 

Be an Issue in the 

Future

To date, antibiotic resistance associated with use in animals has not been a 

significant factor affecting U.S. trade in meat products,67 according to 

officials of USDA’s Foreign Agricultural Service, the Office of the U.S. Trade 

Representative, the U.S. Meat Export Federation, and the U.S. Poultry and 

Egg Export Council. However, the presence of antibiotic residues in meat 

has had some impact on trade.68 In particular, Russia has previously banned 

U.S. poultry because of the presence of tetracycline residues. Furthermore, 

these officials indicated that other issues have been more prevalent in trade 

discussions, including the use of hormones in beef cattle and animal 

67Information obtained in the course of this study identified only Ukraine as having import 

requirements banning fresh or frozen poultry products that were treated with antibiotics for 

growth promotion. However, Ukraine is not a significant market for U.S. poultry.

68Antibiotic residues in meat may occur when antibiotics are improperly used. Traces of the 

antibiotic can remain in the meat tissue, which may affect human health when the meat is 

consumed.
Page 46 GAO-04-490 Antibiotic Use in Animals

diseases such as bovine spongiform encephalopathy (commonly referred 

to as mad cow disease) and avian influenza. For example, the EU currently 

bans U.S. beef produced with hormones. Many other nations ban the 

import of U.S. beef because of the recent discovery of an animal in the 

United States with mad cow disease. 

Although federal government and industry officials stated that antibiotic 

use in animals has not significantly affected U.S. trade to date, we found 

some indication that this issue might become a factor in the future. As 

USDA reported in 2003,69 antibiotic use in animals could become a trade 

issue if certain countries apply their regulations on antibiotic use in 

animals to their imports. For example, according to some government and 

industry officials, the United States’ use of antibiotics could become a trade 

issue with the EU as it phases out its use of all antibiotics for growth 

promotion by 2006. However, the EU is not currently a significant market 

for U.S. meat because of trade restrictions, such as its hormone ban that 

effectively disallows U.S. beef. Similarly, a Canadian task force reported in 

June 2002 that the issue of antibiotic resistance and differences in 

antibiotic use policies could become a basis for countries to place trade 

restrictions on exports of meat from countries that have less stringent use 

policies.70

The issue of antibiotic use in animals and of the potential human health risk 

associated with antibiotic-resistant bacteria have also received 

international attention. For example, in 2003, the Codex Alimentarius 

Commission, an international organization within which countries develop 

food safety standards, guidelines, and recommendations, issued draft 

guidance for addressing the risk of antibiotic resistance in animals. Codex 

also requested that a group of experts assess the risk associated with 

antibiotic use in animals and recommend future risk management options. 

In December 2003, these experts concluded that the risk associated with 

antibiotic-resistant bacteria in food represents a significantly more

69U.S. Department of Agriculture, Economic Research Service, International Trade and 

Food Safety: Economic Theory and Case Studies (Washington, D.C.: 2003).

70Report of the Advisory Committee on Animal Uses of Antimicrobials and Impact on 

Resistance and Human Health. Uses of Antimicrobials in Food Animals in Canada: 

Impact on Resistance and Human Health. A special report prepared at the request of the 

Veterinary Drugs Directorate, Health Canada. June 2002.
Page 47 GAO-04-490 Antibiotic Use in Animals

important human health risk than antibiotic residues—an issue that 

countries have already raised as a trade concern.71

Conclusions Antibiotics have been widely prescribed to treat bacterial infections in 

humans, as well as for therapeutic and other purposes in animals. 

Resistance to antibiotics is an increasing public health problem in the 

United States and worldwide. Published research results have shown that 

antibiotic-resistant bacteria have been transferred from animals to humans. 

In evaluating the safety of animal drugs, FDA considers their effect on 

human health. Such drugs are safe in this regard if there is reasonable 

certainty of no harm to humans when the drug is used as approved. Using 

this critieria, FDA has determined that the potential health risk from 

transference of antibiotic resistance from animals to humans is 

unacceptable and must be a part of FDA’s regulation of animal antibiotics. 

FDA, CDC, and USDA have made progress in their efforts to assess the 

extent of antibiotic resistance from the use of antibiotics in animals 

through both individual and collaborative efforts, including work through 

the Interagency Task Force. However, the effectiveness of these efforts 

remains unknown. FDA has developed guidance to evaluate antibiotics 

used in animals and intends to review all new drug applications and 

antibiotics currently approved for use with animals for this risk to 

determine if it needs to act to ensure that the drugs are safe. Although FDA 

has recently begun the reviews using this approach, its initial reviews have 

been for drugs other than those that are critically important for human 

health. FDA officials do not know how long each review will require. In 

addition, it is not yet known what actions FDA would take if concerns 

became evident. Although the agency has the authority to deny or 

withdraw approval of new or approved animal antibiotics that pose such a 

risk, FDA also has a variety of other options available. However, FDA 

action to prohibit the use of fluoroquinolone antibiotics in poultry has 

continued for more than 3 years. 

Finally, researchers and federal agencies still do not have critical data on 

antibiotic use in animals that would help them more definitively determine 

71Food and Agriculture Organization of the United Nations, Office International des 

Epizooties, and World Health Organization. Joint FAO/OIE/WHO Expert Workshop on NonHuman Antimicrobial Usage and Antimicrobial Resistance: Scientific Assessment. 

December 2003.
Page 48 GAO-04-490 Antibiotic Use in Animals

any linkage between use in animals and emerging resistant bacteria, assess 

the relative contribution of this use to antibiotic resistance in humans, and 

develop strategies to mitigate antibiotic resistance. The experience of 

countries such as Denmark indicates that data collection efforts are helpful 

when making risk-based decisions about antibiotic use in animals. While 

we recognize that there are costs associated with collecting additional data 

on antibiotic use in animals, options exist for collecting these data that are 

not cost-prohibitive. For example, the United Kingdom’s efforts to collect 

national sales data on antibiotic use in animals use relatively few 

resources. In addition, existing federal programs, such as FDA’s ongoing 

monitoring of approved antibiotics and USDA’s CAHFSE, can provide a 

data collection framework that can be expanded to begin collecting the 

needed data. FDA, CDC, and USDA recognize the importance of such 

information and have taken some steps to collect data, although they have 

not yet developed an overall collection strategy. Until the agencies have 

implemented a plan to collect critical data on antibiotic use in animals, 

researchers will be hampered in their efforts to better understand how this 

use affects the emergence of antibiotic-resistant bacteria in humans, and 

agencies will be hampered in their efforts to mitigate any adverse effects.

Recommendations for 

Executive Action

Because of the emerging public health problems associated with antibiotic 

resistance in humans and the scientific evidence indicating that antibioticresistant bacteria are passed from animals to humans, we recommend that 

the Commissioner of FDA expedite FDA’s risk assessments of the 

antibiotics used in animals that the agency has identified as critically 

important to human health to determine if action is necessary to restrict or 

prohibit animal uses in order to safeguard human health.

Additionally, because more data on antibiotic use in animals—such as the 

total quantity used, by class; the species in which they are used; the 

purpose of the use, such as disease treatment or growth promotion; and the 

method used to administer—are needed to further address the risk of 

antibiotic resistance, we also recommend that the Secretaries of 

Agriculture and of Health and Human Services jointly develop and 

implement a plan for collecting data on antibiotic use in animals that will 

adequately (1) support research on the relationship between this use and 

emerging antibiotic-resistant bacteria, (2) help assess the human health 

risk related to antibiotic use in animals, and (3) help the agencies develop 

strategies to mitigate antibiotic resistance.
Page 49 GAO-04-490 Antibiotic Use in Animals

Agency Comments and 

Our Response

We provided USDA and HHS with a draft of this report for review and 

comment. We also provided segments of the draft related to trade matters 

to the Department of State and the Office of the U.S. Trade Representative. 

In their written comments, USDA and HHS generally agreed with the report 

and provided comments on certain aspects of our findings. 

USDA stated that our report recognized the many issues and complexities 

of efforts to address the risk to humans from antibiotic use in animals. The 

department also provided information on the extent of research related to 

antibiotic resistance that it has funded since 1998. We added this 

information to the report. Regarding our conclusion that antibioticresistant salmonella and campylobacter bacteria have been transferred 

from animals to humans, USDA agreed that it is likely that a transfer has 

occurred. However, USDA suggested that some of the studies we cited to 

support that conclusion were, by themselves, inadequate to support a 

causal link. We believe that our conclusion is firmly supported by a body of 

scientific evidence, but we have clarified our description of some studies in 

response to USDA’s comments. On the issue of human health risks, USDA 

commented that we cited few sources of scientific evidence to support the 

view that the human health risks from the transference of antibioticresistant bacteria are minimal. We found that only a few studies have 

concluded that the risk is minimal, while many studies have concluded that 

there is a significant human health risk from the transference. With respect 

to our recommendation that USDA and HHS jointly develop and implement 

a plan for collecting data on antibiotic use in animals, USDA stated that our 

report highlights the importance of the data that the CAHFSE program 

could provide on the impact of antibiotic use in various animal species. 

However, USDA pointed out that additional funding resources would be 

needed to expand CAHFSE and other data collection and research efforts. 

We revised the report to better reflect USDA’s concern about funding.

HHS agreed with our finding that antibiotic-resistant salmonella and 

campylobacter bacteria have been transferred from food animals to 

humans. HHS provided references to additional research studies that 

support our conclusion. We were aware of all of the studies cited by HHS, 

but we did not include them in the report because we believe that our 

conclusion was already amply supported. Regarding our conclusion that 

researchers disagree about the extent of human health risk caused by the 

transference of antibiotic resistance, HHS provided information from an 

unpublished study that found that the course of illness was significantly 

longer for persons with antibiotic-resistant campylobacter cases than for 
Page 50 GAO-04-490 Antibiotic Use in Animals

those with antibiotic-susceptible infections. Most of the studies we 

identified found modest but significant human health consequences, 

similar to those in the unpublished study described in HHS’s comments. 

Regarding our recommendation that the agencies jointly develop and 

implement a plan for collecting data on antibiotic use in animals, HHS 

stated that the most useful and reliable antibiotic use data are those 

maintained by pharmaceutical companies. HHS said current regulations 

would have to be revised to put the data that pharmaceutical companies 

are required to report to FDA in a more relevant format for research on 

antibiotic resistance. As the two agencies develop and implement their plan 

to collect the relevant data, if they agree that pharmaceutical companies 

are an important source, they should take whatever regulatory actions 

might be necessary if the sources they identify will not provide the data 

voluntarily. HHS also proposed that discussions between HHS and USDA 

for improving antibiotic use data collection be conducted through the 

Interagency Task Force on Antimicrobial Resistance. 

We note that while USDA’s comments on antibiotic use data emphasized 

collecting on-farm data through its new CAHFSE program, HHS’s 

comments focused on obtaining data on antibiotic use in animals from 

pharmaceutical companies. We believe these differing approaches 

illustrate the need for USDA and HHS to jointly develop and implement a 

plan to collect data. We agree with HHS that the Interagency Task Force 

could serve as a forum for discussions between USDA and HHS on this 

matter.

USDA’s written comments and our more detailed responses to them are in 

appendix VI. HHS’s written comments are in appendix VII. In addition, 

HHS, USDA, the Department of State, and the Office of the U.S. Trade 

Representative provided technical comments, which we incorporated into 

the report as appropriate.

As agreed with your offices, unless you publicly announce the contents of 

this report earlier, we plan no further distribution until 30 days from the 

date of this letter. At that time, we will send copies of this report to the 

Secretaries of Agriculture and of Health and Human Services and of State; 

the U.S. Trade Representative; and other interested officials. We will also 

provide copies to others upon request. In addition, the report will be 

available at no charge on GAO’s Web site at http://www.gao.gov.
Page 51 GAO-04-490 Antibiotic Use in Animals

If you have any questions about this report, please call Marcia Crosse at 

(202) 512-7119 or Anu Mittal at (202) 512-3841. Other contacts and key 

contributors are listed in appendix VIII.

Marcia Crosse

Director, Health Care—Public

Health and Military Health Care Issues

Anu K. Mittal

Director, Natural Resources 

and Environment
Page 52 GAO-04-490 Antibiotic Use in Animals

Appendix I

Objectives, Scope, and Methodology ApApenednxidexiIs

This report examines the (1) scientific evidence regarding the transference 

of antibiotic resistance from animals to humans through the consumption 

or handling of contaminated meat, and the extent of potential harm to 

human health, (2) progress federal agencies have made in assessing and

addressing the human health risk of antibiotic use in animals, (3) types of 

data that federal agencies need to support research on the human health 

risk of antibiotic use in animals and the extent to which these data are 

collected, (4) use of antibiotics in animals in the United States compared 

with antibiotic use by its key agricultural trading partners and competitors, 

and (5) information that is available on the degree to which antibiotic use 

in animals has affected U.S. trade.

We used the term “animal” to refer to animals raised for human 

consumption, such as cattle, sheep, swine, chickens, and turkeys; the term 

“meat” to refer to beef, lamb, pork, chicken, and turkey; and the term 

“contaminated meat” to refer to meat that contains antibiotic-resistant 

bacteria. We limited the scope of our work to the transference of antibioticresistant bacteria from animals to humans through the consumption or 

handling of contaminated meat. Specifically, we looked at the evidence for 

transference of antibiotic-resistant foodborne intestinal pathogens from 

animals to humans. We did not examine issues related to antibiotics used 

on plants and seafood, antibiotic residues in animals, or the effects of 

antibiotics present in the environment because of the application of animal 

waste to agricultural lands. 

To examine the scientific evidence regarding the transference of antibiotic 

resistance from animals to humans through the consumption or handling of 

contaminated meat, and the extent of harm to human health, we searched 

medical, social science, and agricultural databases, which included the 

Department of Health and Human Services’ (HHS) National Library of 

Medicine, for studies published in professional journals. We identified 

articles published since the 1970s on antibiotic use and resistance in 

animals and humans, as well as articles on antibiotic-resistant foodborne 

illnesses. We interviewed officials from HHS’s Food and Drug 

Administration (FDA) and Centers for Disease Control and Prevention 

(CDC) and the U.S. Department of Agriculture (USDA) to determine how 

these agencies are assessing the human health risk of antibiotic use in 

animals. We also reviewed reports related to the human health risk of 

antibiotic use in animals. Finally, we interviewed officials from relevant 

professional organizations (e.g., the American Medical Association) and 

public health advocacy groups (e.g., the Center for Science in the Public 
Appendix I

Objectives, Scope, and Methodology 

Page 53 GAO-04-490 Antibiotic Use in Animals

Interest) to identify other data or studies on the issue of human health risk 

from antibiotic use in animals.

To determine federal agencies’ progress in assessing and addressing the 

human health risk of antibiotic use in animals, we examined documents 

from FDA, CDC, and USDA. These documents include reports on results 

from the federal government’s antibiotic resistance surveillance program 

and on the progress of the federal Interagency Task Force on Antimicrobial 

Resistance, documents presented in an FDA administrative court 

concerning the agency’s proposal to withdraw the approval of the use of a 

certain antibiotic used in poultry that is also an important antibiotic in 

human medicine, and FDA’s framework to assess the human health risk of 

antibiotic use in animals. 

To examine the types of data that federal agencies need concerning 

antibiotic use in animals in order to support research on the human health 

risk and the extent to which these data are collected, we reviewed federal 

agency documents and reports and interviewed FDA, CDC, and USDA 

officials. In particular, we discussed the status of FDA’s efforts to collect 

data on U.S. antibiotic use in animals, the status of USDA’s programs that 

collect data on antibiotic use, and CDC’s initiatives that would benefit from 

use data. We reviewed foreign government reports to determine how other 

countries use antibiotic use data for research; we also reviewed 

international reports from the World Health Organization (WHO) and the 

Office International des Epizooties (OIE), which provide guidelines on the 

types of use data that countries should collect. We also interviewed 

officials from Denmark, which collects extensive data on antibiotic use in 

animals, and from Canada, which plans to implement a data collection 

system. We discussed the availability of data on U.S. antibiotic use in 

animals with officials from pharmaceutical companies, industry 

associations, state veterinary offices, firms that collect data on antibiotic 

use in animals, and public health advocacy groups.
Appendix I

Objectives, Scope, and Methodology 

Page 54 GAO-04-490 Antibiotic Use in Animals

To examine how the use of antibiotics in animals in the United States 

compares with antibiotic use by its key agricultural trading partners and 

competitors, we obtained and reviewed information on antibiotic use in 

animals for the United States and its key partners and competitors in 

international meat trade. 1

 Using international trade data, we identified the 

European Union (EU) and 11 countries—Australia, Brazil, Canada, China, 

Denmark,2 Hong Kong, Japan, Mexico, New Zealand, Russia, and South 

Korea—as key U.S. trading partners or competitors.3 We obtained 

information on countries’ antibiotic use in animals through discussions 

with officials of USDA’s Animal and Plant Health Inspection Service and 

Foreign Agricultural Service (FAS) and literature searches to identify 

relevant documents. In addition, we discussed antibiotic use in animals 

with government officials from Canada, a leading U.S. trading partner and 

competitor, and Denmark, a leading U.S. trading partner and competitor 

that took significant actions to curtail antibiotic use in animals during the 

late 1990s. We also e-mailed a questionnaire to FAS agricultural attachés in 

the EU and the key trading partner or competitor countries, except Canada 

and Denmark. For Canada and Denmark, we obtained responses to this 

questionnaire from Canadian and Danish government officials as part of 

our visits to these countries. We did not send this questionnaire to 

government officials of the EU and the other nine countries because of 

Department of State and FAS officials’ concerns that antibiotic use in 

animals may be a sensitive issue for some foreign governments and that 

some governments may be suspicious about the questionnaire’s underlying 

purposes; for the same reasons, in completing this questionnaire, the FAS 

agricultural attachés were instructed to not contact foreign government 

officials. As a result, the amount of information we obtained varies by 

country, and we were able to obtain only very limited information on 

antibiotic use in Brazil, China, Hong Kong, Japan, Mexico, Russia, and 

South Korea. We did not independently verify the information reported in 

1

To the extent information was available, we obtained information on policies to regulate 

antibiotic use, quantities of antibiotics sold, and systems to monitor antibiotic use in 

animals and antibiotic resistance associated with this use.

2

Although Denmark is an EU member, we included it in addition to the EU because it is a 

major U.S. competitor in pork exports.

3

To identify these countries, we used USDA’s Foreign Agricultural Service data on (1) 

countries’ trade of beef, pork, and poultry with the United States and (2) countries’ 

worldwide exports of these products. We selected those countries whose share of imports 

or exports of a product was at least 10 percent. In addition, we included China because it is 

a major importer of poultry although it does not trade extensively with the United States.
Appendix I

Objectives, Scope, and Methodology 

Page 55 GAO-04-490 Antibiotic Use in Animals

responses to this questionnaire or other documents, including laws and 

regulations, from the foreign countries. 

To obtain information on antibiotic use in U.S. animal production, we 

reviewed FDA regulations;4

 USDA’s National Animal Health Monitoring 

System reports on management practices, including antibiotic use 

practices in beef cattle and swine production; a University of Arkansas 

study of antibiotic use in broiler chickens; the Animal Health Institute’s 

annual reports on antibiotic use in animals; and a Union of Concerned 

Scientists report.5,6

 We did not independently verify the information 

contained in these reports. In addition, we spoke with officials from state 

veterinarians’ offices and from agricultural industry organizations, 

including the American Veterinary Medicine Association, the National Pork 

Producers Council, the American Meat Institute, the National Cattlemen’s 

Beef Association, the U.S. Poultry and Egg Export Council, the National 

Chicken Council, and pharmaceutical and poultry companies. We also 

visited livestock and poultry farms in Georgia, Maryland, and Pennsylvania. 

We compared the United States’ policies regulating antibiotic use in 

animals with the policies of those key trading partners and competitors for 

which this information was available. In addition, we summarized available 

information on countries’ activities to address antibiotic resistance 

associated with antibiotic use in animals, and, for the United States, we 

developed a list of the antibiotics most commonly used in beef cattle, 

swine, and broiler chickens. 

To examine information that is available on the degree to which antibiotic 

use in animals has affected international trade, we reviewed reports on 

trade and food safety issues from USDA’s Economic Research Service and 

FAS, foreign governments, and international organizations. We also 

examined records of USDA’s Food Safety and Inspection Service to identify 

countries that have requirements concerning antibiotic use for the meat 

they import. In addition, we reviewed the reports and standards of 

international trade organizations, such as the World Trade Organization, 

4

21 C.F.R. parts 520, 522, and 558 (2003).

5

H.D. Chapman, Z.B. Johnson, “Use of Antibiotics and Roxarsone in Broiler Chickens in the 

USA: Analysis for the Years 1995 to 2000,” Poultry Science, 81: 356-364, (2002).

6

M. Mellon, C. Benbrook, and K.L. Benbrook, “Hogging It! Estimates of Antimicrobial Abuse 

in Livestock,” Union of Concerned Scientists, January 2001.
Appendix I

Objectives, Scope, and Methodology 

Page 56 GAO-04-490 Antibiotic Use in Animals

the Codex Alimentarius Commission, and OIE. We discussed antibiotic use 

and other potential trade issues with officials from the Office of the U.S. 

Trade Representative, FAS, and meat industry trade associations.

We also identified several studies on estimates of the potential economic 

impacts of restrictions on antibiotics used in meat production. These are 

described in detail in appendix II.

We conducted our work from May 2003 through April 2004 in accordance 

with generally accepted government auditing standards. 
Page 57 GAO-04-490 Antibiotic Use in Animals

Appendix II

Studies of the Economic Impacts of 

Restricting Antibiotic Uses in Animals ApendxiI

In this appendix we identify and summarize eight recent studies that 

provide estimates of the potential economic impacts of restrictions on 

antibiotics used in livestock production. Specifically, these studies estimate 

the economic effects of a partial and/or total ban of antibiotics used in 

animals. For several decades, antibiotics have been used for a variety of 

production management reasons, from therapeutic uses to increased 

productivity, such as feed efficiency or weight gain. In economic terms, 

higher productivity results in more final product supplied to the market, at 

a lower cost to consumers. Despite the use of a variety of economic 

models, assumptions about model parameters, and data sets, the economic 

impacts on consumers and producers of the studies that we identified were 

generally comparable. Overall, the studies conclude that a ban or partial 

ban on antibiotics in animal production would increase costs to producers, 

decrease production, and increase retail prices to consumers. For example, 

the studies indicate that the elimination of antibiotic use in pork 

production could increase costs to producers ranging from $2.76 to $6.05 

per animal,1

 which translates into increased consumer costs for pork 

ranging from $180 million per year to over $700 million per year. Table 2 

summarizes the eight studies.

1

The WHO study described in this appendix also has estimated a cost of $1.04 per animal; 

however, the study was done to estimate economic impacts on the Danish swine market. 

(See World Health Organization, Impacts of Antimicrobial Growth Promoter Termination 

in Denmark, Department of Communicable Diseases, Prevention and Eradication and 

Collaborating Centre for Antimicrobial Resistance in Foodborne Pathogens, 2003.)
Appendix II

Studies of the Economic Impacts of 

Restricting Antibiotic Uses in Animals

Page 58 GAO-04-490 Antibiotic Use in Animals

Table 2: Economic Studies That Estimate the Effects of Restrictions on Antibiotic Use

Economic impacts

Economic study Purpose of the study Year Producers Consumers

World Health 

Organization (WHO), 

Impacts of 

Antimicrobial Growth 

Promoter Termination 

in Denmark

To review the economic 

impacts resulting from 

the Danish ban of the 

use of antibiotics for 

growth promotion 

purposes in swine and 

poultry production.

2003 Cost increase of $1.04 per 

swine or 1 percent of total 

production costs.

No cost changes for poultry.

Hayes and Jensen, 

“Lessons from the 

Danish Ban on FeedGrade Antibiotics,” 

Center for 

Agricultural and Rural 

Development

To determine the 

economic impacts of a 

ban on antibiotics in pork 

production in the United 

States from the 

experience with such a 

ban in Denmark.

2003 Costs increase by $4.50 per 

head in first year.

Total 10-year cost over $700 

million.

Retail price increases by 2%.

Miller et al., 

“Productivity and 

Economic Effects of 

Antibiotics Used for 

Growth Promotion in 

U.S. Pork 

Production,” Journal 

of Agricultural and 

Applied Economics

To estimate the net 

benefit of antibiotics used 

for growth promotion to 

swine producers in the 

United States using the 

1990 and 1995 NAHMS 

swine survey data.a

2003 Increased profits of $0.59 per 

marketed swine or 9% 

profitability.

Miller et al., 

“Producer Incentives 

for Antibiotic Use in 

U.S. Pork 

Production,” 

American Agricultural 

Economics 

Association Annual 

Meetings

To validate the 

productivity and 

economic impacts of 

antibiotic use for swine 

producers at the farm 

level using the NAHMS 

2000 survey.

2003 Four scenarios:b

• Ban on AGP: profits decrease 

by $3,813

• Ban on ADP: profits increase 

by $2703

• Ban on AGP and ADP: profits 

decrease by $1128

• Limitation of AGP and ADP: 

Profits increase by $12,438

Brorsen, 

Lehenbauer, Ji, and 

Conner, “Economic 

Impacts of Banning 

Subtherapeutic Use 

of Antibiotics in 

Swine Production,” 

Journal of 

Agricultural and 

Applied Economics

To estimate the 

economic impacts on 

producers and 

consumers of a ban on 

the use of antibiotics in 

swine production.

2002 Costs would increase by $2.37 - 

$3.11 per hog with an average of 

$2.76 per hog.

Total costs would be $153.5 

million per year in the short run 

and $62.4 million per year in the 

long run.

Costs to consumers increase by 

$89 million per year in the short run 

to $180 million per year in the long 

run.
Appendix II

Studies of the Economic Impacts of 

Restricting Antibiotic Uses in Animals

Page 59 GAO-04-490 Antibiotic Use in Animals

Source: GAO analysis of sources cited.

a

NAHMS is the National Animal Health Monitoring System. 

b

Within these scenarios, Miller et al. define AGP as antibiotics used for growth promotion and ADP as 

antibiotics used for disease prevention. The annual estimates of economic impacts for these scenarios 

are for a producer that has a 1,020-head barn of swine. A swine producer could have many such barns 

in his/her operation.

c

The National Research Council estimates of retail price increases are ranges based on whether 

consumers would substitute other meat. The lower change in price assumes that substitution of other 

meat mitigates the price impact by 50 percent, while the higher change in retail price assumes no 

substitution.

d These estimates are in 1984 dollars.

Mathews, Jr., 

“Economic Effects of 

a Ban Against 

Antimicrobial Drugs 

Used in U.S. Beef 

Production,” Journal 

of Agricultural and 

Applied Economics

To examine the 

economic effects of a 

ban on antibiotic use in 

U.S. beef production on 

two policy alternatives—

a partial ban and a full 

ban.

2002 Partial ban: Cattle prices 

increase by 0.49 percent. 

Producer income declines by 

$15 million.d

Full ban: Cattle prices increase 

by 3.32 percent. Producer 

income declines by $113.6 

million.d

Partial ban: Costs to consumers 

increase by $54.7 million.d

Full ban: Costs to consumers 

increase by about $361 million.d

Hayes, Jensen, 

Backstom, and 

Fabiosa, “Economic 

Impact of a Ban on 

the Use of Over-theCounter Antibiotics,” 

Center for 

Agricultural and Rural 

Development

To estimate the likely 

economic impacts of a 

ban on antibiotics in the 

U.S. pork industry based 

on the impacts of such a 

ban in Sweden.

1999 Costs would increase by $5.24 - 

$6.05 per head.

Net profit declines by 

$0.79/head.

Total net present value of 

forgone profits over 10 years 

declines by $1.039 billion.

Retail price would increase by 5 

cents per pound.

Nationally, annual increase of 

consumer costs of $748 million.

National Research 

Council

“Costs of Eliminating 

Subtherapeutic Use 

of Antibiotics” in The 

Use of Drugs in Food 

Animals: Benefits 

and Risk

To examine the 

economic costs to 

consumers of the 

elimination of 

subtherapeutic use of 

antibiotics for poultry, 

beef, and pork.

1999 Retail meat price increases (cents 

per pound):c

Chicken: (1 – 3)

Turkey: (2 – 3) 

Pork: (3 – 6) 

Beef: (3 – 6)

Total consumer costs for pork:

$382 million - $764 million per year.

For all meat products, consumer 

costs increase by $1.2 billion to $2.5 

billion per year.

(Continued From Previous Page)

Economic impacts

Economic study Purpose of the study Year Producers Consumers
Appendix II

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Page 60 GAO-04-490 Antibiotic Use in Animals

While these market effects are important to both producers and consumers 

of livestock products, they must be balanced against the health care costs 

of antibiotic resistance due to agricultural uses of antibiotics. Potential 

health costs imposed by increased antibiotic resistance include more 

hospitalizations, higher mortality rates, and higher research costs to find 

new and more powerful drugs.2

 From the point of view of proposals to 

reduce antibiotic use, these potential costs represent the benefits from 

reduced antibiotic use. These costs to society, however, are difficult to 

measure because of limited data on antibiotic use and resistance as well as 

the problematic nature of measuring the value of a human life. Moreover, 

while there are some estimates of the costs of antibiotic resistance from 

both medical and agricultural sources, no estimates exist that directly link 

the human health costs of antibiotic resistance with antibiotics used in 

animal production. Nevertheless, studies that have examined the costs of 

antibiotic resistance from all sources have found a wide range of estimates 

running into the millions and billions of dollars annually.3

 For example, one 

recent study (2003) estimated that the health cost to society associated 

with resistance from only one antibiotic, amoxicillin, was $225 million per 

year.4

 

We discuss the eight studies we reviewed in reverse chronological order, 

from 2003 to 1999. Most examine restrictions on antibiotics in the swine 

industry, but a few look at the beef and poultry industries as well. All of the 

studies measure the economic impacts of antibiotic restrictions on 

domestic U.S. markets, except the WHO study of the antibiotic restrictions 

recently imposed by Denmark. Also, most studies estimate only domestic 

economic impacts, not impacts on international trade. 

2

Ramanan Laxminarayan, “Fighting Antibiotic Resistance: Can Economic Incentives Play a 

Role?” Resources, Spring 2001, Issue 143.

3

Phelps (1989) estimated that the annual economic costs of drug resistance range from a 

best-case scenario of $100 million to a worst-case scenario of $30 billion, with the wide 

range of estimates accounted for by different assumptions about the economic value of a 

human life. Also, a study done by the Office of Technology Assessment in 1995 estimated 

that the cost of antibiotic resistance for six different strains of antibiotic bacteria reached 

about $1.3 billion in 1992 dollars. 

4

E.H. Elbasha, “Deadweight Loss of Bacterial Resistance Due to Overtreatment,” Health 

Economics, 2003, 12(2): 125-138.
Appendix II

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Page 61 GAO-04-490 Antibiotic Use in Animals

WHO (2003) Review of the 

Economic Impacts of 

Antibiotics for Growth 

Promotion in Denmark

In 2002, WHO convened an international expert panel to review, among 

other issues, the economic impact resulting from the Danish ban of 

antibiotics for growth promotion, particularly in swine and poultry 

production.5

 As part of this effort, Denmark’s National Committee for Pigs 

estimated that the cost of removing antibiotic growth promoters in 

Denmark totaled about $1.04 per pig, or a 1 percent increase in total 

production costs. In the case of poultry, however, there was no net cost 

because the savings associated with not purchasing these antibiotics offset 

the cost associated with the reduction in feed efficiency. Components of 

these costs included excess mortality, excess feeding days, increased 

medication, and increased workload.

A subsequent study by Jacobsen and Jensen (2003) used these costs as part 

of the agriculture sector of a general equilibrium model to estimate the 

impact on the Danish economy of the termination of antibiotic growth 

promoters.6

 The model used these cost assumptions in a baseline scenario 

that projects the likely development of the Danish economy to 2010. 

The results of the model indicated a small reduction in pig production of 

about 1.4 percent per year and an increase in poultry production of about 

0.4 percent. The authors explain that the increase in poultry production 

occurred because of the substitutability of these meats in consumption. In 

addition, this research included estimates of the consequences of removing 

antibiotic growth promoters on the export market. The model showed that 

exports of pork were forecast to be 1.7 percent lower than they would be in 

the absence of these growth promoters, while poultry exports would 

increase by about 0.5 percent.

The authors explained that some costs associated with modifications to 

production systems were difficult to measure and were not included in the 

analysis, although they may have been substantial for some producers. 

They also stated that the analysis does not take into account the possible 

positive effect that the removal of antibiotic growth promoters may have 

5

World Health Organization, Impacts of Antimicrobial Growth Promoter Termination in 

Denmark, Department of Communicable Diseases, Prevention and Eradication and 

Collaborating Centre for Antimicrobial Resistance in Foodborne Pathogens, 2003.

6

L.B. Jacobsen and H.G. Jensen, “Sector and Economy Wide Effects of Terminating the Use 

of Antimicrobial Growth Promoters in Denmark,” In: International Invitational Symposium; 

Beyond Antimicrobial Growth Promoters in Food Animal Production, November 6-7, 2002 

(subsequently revised, 2003), Foulum, Denmark. 
Appendix II

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Page 62 GAO-04-490 Antibiotic Use in Animals

had on consumer demand, both in the domestic and in the export markets. 

Moreover, they added that any costs must be set against the likely human 

health benefits to society.

Hayes and Jensen (2003) 

Study Based on the Danish 

Ban of Feed-Grade 

Antibiotics in the Pork 

Industry

In 2003, using a 1999 study by Hayes et al. of the potential economic 

impacts of a U.S. ban based on the ban in Sweden, as described below, and 

a recent ban on feed-grade antibiotics in Denmark, Hayes and Jensen 

estimated the economic impacts of a similar ban in the United States.7

 In 

1998, the Danish government instituted a voluntary ban on the use of 

antibiotics in pork production at the finishing stage, and in 2000 it banned 

antibiotics for growth promotion at both the weaning and the finishing 

stages. The results of the ban in Denmark, however, may be more 

applicable than the Swedish experience because, like the United States, 

Denmark is one of the largest exporters of pork and has somewhat similar 

production practices.8

 The authors compared the econometric results of a 

U.S. baseline without a ban with projected results based on assumptions 

taken from the ban in Denmark. Many of the same technical and economic 

assumptions that were used in the Swedish study were also used for the 

impacts based on the Danish ban. For instance, the authors included a sortloss cost of $0.64 per animal, a similar assumption for loss of feed 

efficiency, and decreases in piglets per sow.9

 Other key assumptions and 

features unique to the study include the following:

• the use of only one case or scenario—a “most-likely” scenario—unlike 

the study based on the Swedish ban;

• increased costs of $1.05 per animal at the finishing stage and $1.25 per 

animal at the weaning stage;

7

Dermot J. Hayes and Helen H. Jensen, “Lessons from the Danish Ban on Feed-Grade 

Antibiotics,” Briefing Paper 03-BP 41, Center for Agricultural and Rural Development, Iowa 

State University, Ames, Iowa, June 2003. 

8

While the United States and Denmark are both leading pork exporters, their market 

structures are different. In Denmark, unlike in the United States, farmer cooperatives 

dominate production, processing, and distribution systems.

9

Sort-loss costs represent discounts or penalties for increased weight variability for 

marketing swine that are either too light or too heavy. The Swedish experience indicated 

that removal of antibiotics in feed increased this variability at marketing. However, because 

they were able to influence the packers to accept more light weight pigs, Swedish producers 

actually did not have a problem with sort loss. 
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• a vaccine cost of $0.75 per animal; and 

• a capital cost of about $0.55 per animal; 

According to the study, a major economic impact in the U.S. pork market of 

a ban similar to the Danish ban would be a cost increase of about $4.50 per 

animal in the first year. Across a 10-year period, the total cost to the U.S. 

pork industry was estimated to be more than $700 million. With a lower 

level of pork production, retail prices would increase by approximately 2 

percent. The authors conclude that a ban at the finishing stage would 

create very few animal health concerns, while a ban at the weaning stage 

would create some serious animal health concerns and lead to a significant 

increase in mortality. They also note that, as happened immediately 

following the ban at the weaning stage in Denmark, the total use of 

antibiotics in the United States at this production stage may rise. 

Miller et al. (2003) Study 

Using 1990 and 1995 

NAHMS Data on the 

Economic Effects of 

Antibiotics Used for Growth 

Promotion in U.S. Pig 

Production

Miller et al. (2003) used 1990 and 1995 National Animal Health Monitoring 

System (NAHMS) swine survey data to estimate the net benefit of 

antibiotics used for growth promotion to swine producers.10 The NAHMS 

database provides statistically valid estimates of key parameters related to 

the health, management, and productivity of swine operations in the United 

States.11 The authors used econometric methods to estimate the 

relationships between growth-promoting antibiotics and productivity 

measures, such as average daily weight gain (ADG) and feed conversion 

ratio (FCR), for grower/finisher pigs. Using these productivity measures, 

predictions on performance were then generated for an independent, 

medium-sized, midwestern farrow-to-finish pork producer in 1995. The 

performance figures were expressed in economic terms, such as 

profitability, using a swine enterprise budgeting model. The study includes 

the following key features and assumptions:

10Gay Y. Miller, Kenneth A. Algozin, Paul E. McNamara, and Eric J. Bush, “Productivity and 

Economic Effects of Antibiotics Used for Growth Promotion in U.S. Pork Production,” 

Journal of Agricultural and Applied Economics, 35,3(December 2003): 469-482. 

11The National Animal Health Monitoring System (NAHMS) is a program operated by 

veterinary and animal science professionals at USDA’s Center for Animal Health Monitoring. 

A primary function of this branch of USDA is to make periodic surveys and assessments of 

animal health management practices on commercial livestock farms across the United 

States.
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Page 64 GAO-04-490 Antibiotic Use in Animals

• The productivity measures estimated were ADG, FCR, and mortality 

rate (MR) during the grower/finisher stage of swine production.

• Explanatory variables included in the model were regional identifiers, 

size of operation, market structure variables, number of rations, 

mortality rate, number of days antibiotics were administered, number of 

antibiotics fed, number of diseases diagnosed in last 12 months, among 

others.

• The ADG and FCR equations were estimated jointly using the seemingly 

unrelated regression procedure.

• Because the theory as to an exact specification was unknown, the MR 

equation was estimated using a backward-stepwise linear regression. 

The authors estimated that increases in annual returns above costs from 

antibiotics for a 1,020-head finishing barn was $1,612, or $0.59 per swine 

marketed. This represents an improved profitability of approximately 9 

percent of net returns in 2000 for Illinois swine finishing operations. The 

authors also found that there is substitutability between antibiotics as 

growth promoters and other production inputs (such as number of rations) 

that could reduce the negative influence of removing antibiotics.

Miller et al. (2003) Study 

Using 2000 NAHMS Data to 

Estimate the Productivity 

and Economic Impacts of 

Antibiotic Use in U.S. Pig 

Production

In an updated study, Miller et al. (2003) estimated the combined effects of 

antibiotics used for growth promotion (AGP) and antibiotics used for 

disease prevention (ADP) in pork production using the NAHMS 2000 swine 

survey.12 Specifically, the authors measured the productivity and the 

economic impacts of these antibiotics on grower/finisher pigs for 

individual swine producers. The authors evaluated four scenarios, using 

varying degrees of bans of both AGP and ADP: (1) a ban on AGP, (2) a ban 

on ADP, (3) a ban on both AGP and ADP, and (4) a limitation on AGP and 

ADP to levels that maximize production. These scenarios were chosen 

because antibiotics that are used for different purposes have different 

impacts on productivity, improving it on one dimension while possibly 

diminishing it on another. First, the authors estimated four pork 

productivity dimensions related to the use of antibiotics using an 

12Gay Y. Miller, Xuanli Liu, Paul E. McNamara, and Eric J. Bush, “Producer Incentives for 

Antibiotic Use in U.S. Pork Production,” paper prepared for presentation at the American 

Agricultural Economics Association Annual Meeting, Montreal, Canada, July 2003.
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Page 65 GAO-04-490 Antibiotic Use in Animals

econometric model. Second, using the estimated productivity measures 

from the econometric model, they estimated economic impacts to pork 

producers for each antibiotic ban scenario using a spreadsheet farm budget 

model. The study includes the following key features and assumptions:

• Pork productivity was measured using four measures of productivity, 

including average daily weight gain, feed conversion ratio, mortality 

rate, and lightweight rate.

• These productivity measures were estimated using seemingly unrelated 

regression analysis and are modeled from the perspective of possible 

structural relationships among the measures.

• The study used the NAHMS 2000 study, which provides the most recent 

data available to investigate productivity impacts and impacts on farm 

costs and profitability.

Overall, the authors confirmed their earlier findings that a ban would likely 

cause substantial short-term losses to producers. However, decreasing the 

use of certain antibiotics to a more desirable level may be implemented 

without major losses. For scenario 1, a total ban on AGP would cost 

producers $3,813 in profits annually.13 For scenario 2, a ban on ADP would 

slightly improve profits by a gain of $2703 annually. For scenario 3, a ban on 

both AGP and ADP would lower producer profits by $1128 annually. For 

scenario 4, where AGP and ADP are applied at levels where swine 

productivity is maximized, producers would gain $12,438 annually 

compared with no antibiotic use. The authors conclude that restrictions on 

classes of AGP, the amount of time antibiotics are fed, and restrictions on 

ADP many be implemented by producers without major losses. However, 

they also note that some time dimensions ignored in their study may be 

important and that their use of nonexperimental data requires careful 

interpretation.

13Each scenario in the model estimates profit for a 1,020-head barn of swine. A swine 

producer, however, could have many such barns in his/her operation.
Appendix II

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Brorsen et al. (2002) Study 

on Economic Effects of a 

Ban on the Use of 

Antibiotics for Growth 

Promotion in Swine 

Production 

Brorsen et al. (2002) used a model similar to one developed by Wohlgenant 

(1993) to estimate the economic impacts on producers and consumers of a 

ban on antibiotics used for growth promotion in swine production.14 The 

authors used a model that allowed for feedback between beef and pork 

markets and measured changes in producer and consumer surplus 

resulting from shifts in both supply and demand. Moreover, the authors 

extended their two-commodity beef and pork model to include poultry. In 

their model, changes in production costs due to banning the use of 

antibiotics for growth promotion are measured indirectly by the net 

benefits from their use. The study includes the following key features and 

assumptions:

• The ban considered in this model is a complete ban on all antibiotics in 

feed.

• The effects of using antibiotics for growth promotion were assumed to 

be from improvements in (1) feed efficiency over drug cost, (2) reduced 

mortality rate, and (3) reduced sort-loss at marketing.

• The authors assumed a $45.00 per hundredweight market price for hogs.

• All parameters (i.e., demand and supply elasticities) used to solve the 

model were based on other economic studies, except the parameter that 

represented the change in production costs. Once these were obtained, 

retail quantity, retail price, farm quantity, and farm price were 

determined simultaneously.

• An econometric model was used to obtain the economic benefit from 

the improvement in feed-to-gain conversions in swine production.

• The mortality benefit in swine was assumed to range from 0 percent, to 

0.75 percent (most likely), to 1.5 percent.

14B. Wade Brorsen, Terry Lehenbauer, Dasheng Ji, and Joe Conner, “Economic Impacts of 

Banning Subtherapeutic Use of Antibiotics in Swine Production,” Journal of Agricultural 

and Applied Economics, 34,3 (December 2002): 489-500; and M.K. Wohlgenant “Distribution 

of Gains from Research and Promotion in Multi-Stage Production Systems: The Case of the 

U.S. Beef and Pork Industries,” American Journal of Agricultural Economics 75 (1993): 

642-651.
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• Net benefits of the use of antibiotics for growth promotion were 

estimated by summing the results of a simulation exercise based on the 

probability distributions of the three sources of economic benefits at the 

industry level.

The authors estimated that economic costs to swine producers from a ban 

on antibiotics used for growth promotion would range from $2.37 per hog 

to $3.11 per hog, with an average cost of $2.76 per hog. For swine 

producers, the estimated annual costs would be approximately $153.5 

million in the short run to $62.4 million in the long run. Estimated annual 

costs to pork consumers would increase by about $89 million in the short 

run to $180 million in the long run. 

Mathews, Jr. (2002) Analysis 

of the Economic Effects of a 

Ban on Antibiotics in U.S. 

Beef Production

Mathews, Jr. (2002) examined the economic effects of a ban on antibiotic 

use in U.S. beef production using two policy alternatives—a partial ban and 

a full ban.15 To estimate these effects, the author developed a series of 

economic models, including a firm-level, cost-minimization model that 

minimizes the cost of feeding cattle to final output weights for a base case, 

a full ban, and a partial ban (banning only selected antibiotics) scenario. 

Imbedded in this model is a growth function that incorporates the 

interaction between the growth rate of cattle and feed efficiency. The firmlevel effects were then aggregated across firms in a partial equilibrium 

framework to estimate national cattle supply, price, and value of 

production for the three scenarios. The study includes the following key 

features and assumptions:

• Variables included in the growth function were lagged average daily 

weight gain, feed efficiency, seasonal variables, and an interaction 

variable of average weight gain and feed efficiency. The growth model 

forms a “dynamic” link to the cost-minimization model by accounting 

for the impacts of recent feeding experiences. 

• In the cost-minimization model, feed costs were minimized, subject to 

protein levels and other feed constraints. The model finds the minimum 

cost for feeding a steer to a final weight estimated from the embedded 

growth function.

15Kenneth H. Mathews, Jr., “Economic Effects of a Ban Against Antimicrobial Drugs Used in 

U.S. Beef Production,” Journal of Agricultural and Applied Economics, 34, 3 (December 

2002): 513-530. 
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• The resulting model allowed final cattle weights, feeding costs, and the 

number of cattle fed per year to vary, resulting in livestock supplies that 

are endogenous to the model. 

• In the partial-ban scenario, substitute antibiotics were assumed to be 

functionally equivalent to and twice as costly as in the base scenario.

• Data for the aggregate analysis included annual average all-cattle prices 

and commercial beef production for the period 1975 through 1990. A 

base scenario was estimated using parameter and final steer weight 

estimates from the growth model for each quarter over an 11-year 

period, from January 1990 through January 2001.

Results of the partial-ban scenario indicated that aggregate annual income 

would decrease by nearly $15 million for producers, while annual 

consumer costs would increase by $54.7 million.16 For the full ban, a 4.2 

percent decline in beef production would yield a 3.32-percent increase in 

the price of cattle, from $42.60 to $47.12 per hundredweight. Also, the full 

ban translates into an annual consumer cost increase of $361 million. The 

author noted that the study did not take into account any effects of a ban or 

partial ban on trade in beef products.

Hayes et al. (1999) Study 

Based on the Swedish Ban 

of Antibiotics in the Pork 

Industry 

A study issued in 1999 by Hayes et al. at Iowa State University estimated 

the potential economic impacts of a ban on the use of antibiotics in U.S. 

pork production based on assumptions from a Swedish ban in 1986.17 To 

estimate baseline results, the authors used a simultaneous econometric 

framework of the U.S. pork industry that included several production and 

marketing segments: live inventory and production, meat supply, meat 

consumption, meat demand, and retail price transmission. The baseline 

results, or results with no change in antibiotic use, were compared to a 

range of estimates of a ban on antibiotics in pork production in the United 

States based on a set of technical and economic assumptions taken from 

the Swedish experience. These simulations included three different 

scenarios: a “most likely,” a “best-case,” and a “worst-case” scenario if the 

16All estimates for this study are in 1984 dollars.

17Dermot J. Hayes, Helen H. Jensen, Lennart Backstrom, and Jay Fabiosa, “Economic 

Impact of a Ban on the Use of Over-the-Counter Antibiotics, ” Staff Report 99-SR 90, Center 

for Agricultural and Rural Development, Iowa State University, Ames, Iowa, December 1999.
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ban were to be implemented in the United States. The key features and 

assumptions of the model for the “most likely” case included the following:

• a 10-year projection period from 2000 to 2009 from a 1999 baseline, with 

deviations from the baseline in the projection period reflecting the 

technical and economic assumptions taken from the Swedish ban;

• the pork, beef, and poultry markets, although the model assumed no 

change in the regulation of antibiotics on beef and poultry;

• technical assumptions: feed efficiency for pigs from 50 to 250 pounds 

declines by 1.5 percent, piglet mortality increases by 1.5 percent, and 

mortality for finishing pigs increases by 0.04 percent. Also, the “most 

likely” case extends weaning age by 1 week and piglet per sow per year 

decrease by 4.82 percent.

• veterinary and therapeutic costs would increase by $0.25 per pig, net of 

the cost for feed additives;

• additional capital costs would be required because of additional space 

needed for longer weaning times and restricted feeding, including $115 

per head for nursery space and $165 per head for finishing space;

• an estimated penalty of $0.64 per head for sort-loss costs; and

• input markets, such as the cost of antibiotics, are exogenous or not a 

part of the modeling system.

The authors in their “most likely” scenario estimated that the effects of a 

ban on the use of antibiotics would increase production costs by $6.05 

initially and $5.24 at the end of the 10-year period modeled. Because the 

supply of pork declines, however, net profit to farmers would decline by 

only $0.79 per head. Over a 10-year period, the net present value of forgone 

profits would be about $1.039 billion. For consumers, the retail price of 

pork increases by $0.05 per pound, which sums to a yearly cost of about 

$748 million for all consumers.

The authors also cited four important limitations to their study: (1) the 

estimated impacts represent an “average” farm and may mask wide 

differences across farms; (2) technical evidence from the Swedish 

experience must be regarded with caution as an indicator of what might 

happen in the United States; (3) consumers only respond to changes in the 
Appendix II

Studies of the Economic Impacts of 

Restricting Antibiotic Uses in Animals

Page 70 GAO-04-490 Antibiotic Use in Animals

price of pork; however, the model does not take into account how such a 

ban would affect the prices of beef and poultry; and (4) there was no 

attempt to factor in the positive effects of such a ban on consumer 

willingness to pay for pork produced without the use of feed-grade 

antibiotics.

National Research Council’s 

(1999) Economic Analysis 

of the Costs of Eliminating 

Subtherapeutic Use of 

Antibiotics in Animals

The National Research Council (NRC) examined the economic costs to 

consumers of the elimination of all subtherapeutic use of antibiotics in a 

chapter of a 1999 report entitled The Use of Drugs in Food Animals: 

Benefits and Risks.

18 Instead of measuring the consequences of eliminating 

antibiotics on farm costs and profits, NRC decided that a more viable 

alternative would be to measure costs to consumers in terms of the higher 

prices that would be passed on to consumers. According to NRC, this 

measurement strategy was followed for several reasons: changes in 

production costs do not necessarily translate into lower profits; depending 

on management practices, not all producers rely on these antibiotics to the 

same extent and would not all be equally affected by a ban; and some 

producers, for example those who produce for special niche markets, may 

actually benefit from such a ban.19 The study includes the following key 

features and assumptions:

• All cost increases are passed on to consumers in terms of percentage 

price changes.

• The model measures how much consumers would need to spend in 

order to maintain a similar level of consumption as before the ban.

• No change in consumption because of a ban on antibiotics would occur.

18National Research Council, “Costs of Eliminating Subtherapeutic Use of Antibiotics,” 

Chapter 7, in The Use of Drugs in Food Animals: Benefits and Risk, National Academy 

Press, Washington, D.C., 1999, 179-187. Although the precise definition is the subject of 

some debate, subtherapeutic use refers to antibiotic use in animal production to improve 

animal performance, such as enhanced growth rates or improved feed efficiency, whereas 

therapeutic use refers to antibiotics used to treat specific health problems.

19The NRC cites Colemon Natural Beef of Colorado, a company that raises its beef without 

antibiotic treatments or exogenous growth promoters, as an example of such a company. 
Appendix II

Studies of the Economic Impacts of 

Restricting Antibiotic Uses in Animals

Page 71 GAO-04-490 Antibiotic Use in Animals

• Per capita costs are estimated as the product of three items: (1) 

percentage increase in annual production costs, (2) retail prices, and (3) 

per capita annual retail quantity sold.

• Annual costs of a ban were estimated for four domestic retail markets—

chicken, turkey, beef, and pork—as well as a total cost for all meat.

NRC estimated that the average annual cost per capita to consumers of a 

ban on all antibiotic use was $4.84 to $9.72. On a commodity retail price 

basis, the change in price for poultry was lowest, from $0.013 per pound to 

$0.026 per pound; for pork and beef, prices ranged from $0.03 per pound to 

$0.06 per pound. Retail pork price increases ranged from $0.03 per pound 

to $0.06 per pound. Total national additional costs per year for pork 

consumption ranged from $382 million to $764 million, depending on 

assumptions about meat substitutes. As for all meat products combined, 

total consumer cost increases ranged from $1.2 billion to $2.5 billion per 

year. Finally, NRC noted that the reduction in profits and industry 

confidence that would result from such a ban may cause a reduction in 

research, and that society would lose the research benefits. Also, to 

determine whether this cost increase would be justified, the amount should 

be compared with the estimated health benefits.
Page 72 GAO-04-490 Antibiotic Use in Animals

Appendix III

FDA’s Procedures for Evaluating the 

Importance of an Animal Drug for Human 

Health ApendxiI

As part of the risk estimation outlined in Guidance for Industry #152, FDA 

developed a framework for evaluating the importance of an antibiotic to 

human medicine. FDA has ranked antibiotics as either critically important, 

highly important, or important. These rankings are based on five criteria, 

which are ranked from most (criterion 1) to least important (criterion 5):

1. The antibiotic is used to treat enteric pathogens that cause foodborne 

disease. 

2. The antibiotic is the sole therapy or one of the few alternatives to treat 

serious human diseases or is an essential component among many 

antibiotics in the treatment of human disease.

3. The antibiotic is used to treat enteric pathogens in nonfoodborne 

disease.

4. The antibiotic has no cross-resistance within the drug class and an 

absence of linked resistance with other drug classes.1

5. There is difficulty in transmitting resistance elements within or across 

genera and species of organisms.

Antibiotics that meet both of the first two criteria are considered by FDA to 

be critically important to human medicine. Drugs that meet either of the 

first two criteria are considered highly important to human medicine. 

Drugs that do not meet either of the first two criteria but do meet one or all 

of the final three criteria are considered important to human medicine. Of 

the 27 classes of animal drugs relevant to human health, 4 were ranked 

critically important, 18 highly important, and 5 important. The status of a 

particular antibiotic may change over time. For example, a drug may be 

considered to be critically important to human health because it is the sole 

therapy. Later, if new antibiotics become available to treat the same disease 

or diseases, the drug may be downgraded in its importance to human 

health.

1

Cross-resistance refers to the transmission of antibiotic-resistant determinants between 

bacterial species or genera and does not refer to transmission of antibiotic-resistant 

organisms between animals and humans.
Page 73 GAO-04-490 Antibiotic Use in Animals

Appendix IV

Information on Selected Countries’ Activities 

to Address Animal-Related Antibiotic 

Resistance ApendxiIV

This appendix provides information on efforts to address antibiotic 

resistance associated with antibiotic use in animals for the United States 

and some of its key trading partners and competitors. For the United 

States, more detailed information on these activities is in the letter portion 

of this report. For the United States’ key trading partners and competitors, 

to the extent that information was available, we summarized the countries’ 

activities and described antibiotic resistance surveillance systems and 

antibiotic use data collection systems. 

In addition, table 3 presents information on the total amount of antibiotics 

sold or prescribed for use in animals for the United States and three trading 

partners and competitors for which this information was available. 

Specifically, it shows 2002 antibiotic sales data for the countries that we 

identified as having government data collection systems on antibiotic use 

with the available data. Although the United States does not have a 

government system, we included information collected by the Animal 

Health Institute for comparison. Total meat production is also shown to 

represent the size of the animal production industries in these countries. 

Table 3: Antibiotic Sales and Meat Production, 2002

Source: Danish Integrated Antimicrobial Resistance Monitoring and Research Programme, Veterinary Institute, the New Zealand Food 

Safety Authority, the United Kingdom Veterinary Medicines Directorate, the Animal Health Institute, and the Food and Agriculture 

Organization of the United Nations.

Note: The antibiotic amounts do not include ionophores, an antibacterial that is a unique drug product 

developed for animal production and not related to traditional antibiotics. 

a

Denmark’s information is based on actual use of antibiotics. The other information is based on 

antibiotics sold for use in animals and includes limited use in other species.United States

Antibiotic sales 

(metric tons of active 

ingredient)

Metric tons of meat 

production (in millions)

Percent of world 

total meat 

production

Denmarka 94 2.1 1

New Zealand 106 1.3 1

United 

Kingdom 433 3.3 1

United States 5,896 39.0 16
Appendix IV

Information on Selected Countries’ 

Activities to Address Animal-Related 

Antibiotic Resistance 

Page 74 GAO-04-490 Antibiotic Use in Animals

Overview of activities. In 1999, federal agencies formed the Interagency 

Task Force on Antimicrobial Resistance to address antibiotic resistance 

issues.1

 In October 2003, FDA issued guidelines for assessing the safety of 

animal drugs (Guidance for Industry #152). FDA is conducting risk 

assessments of some antibiotics important in human medicine.

Antibiotic-resistance surveillance systems. FDA, CDC, and USDA collect 

information on antibiotic-resistant bacteria in humans, retail meat, and 

animals through the National Antimicrobial Resistance Monitoring System 

(NARMS).

Antibiotic use data collection systems. The Animal Health Institute, a 

trade association representing veterinary pharmaceutical companies, 

publishes the only publicly available data on the amount of antibiotics sold 

annually for use in animals. The Animal Health Institute collects these data 

from its member companies, which represent about 85 percent of the 

animal drug sales in the United States. The data show the amount of 

antibiotics sold by antibiotic class, but certain classes are reported 

together to abide by company disclosure agreements. See table 3 for 

information on the amount of antibiotics sold in the United States during 

2002. In addition, the United States collects some on-farm data through 

USDA’s National Animal Health Monitoring System (NAHMS) and 

Collaboration in Animal Health, Food Safety, and Epidemiology (CAHFSE) 

programs. 

Australia Overview of activities. In 1998, Australia established the Joint Expert 

Technical Advisory Committee on Antibiotic Resistance to provide 

independent expert scientific advice on the threat to human health of 

antibiotic-resistant bacteria caused by use in both animals and humans.2

 

Australia has begun to review the approved uses of antibiotics important in 

human medicine to determine if changes are needed. Australia’s review 

process includes performing a public health and an efficacy assessment. 

Like the United States’ risk assessment approach, Australia’s public health 

assessment considers the hazard, exposure, and potential impact of the 

1

In January 2001, the task force issued A Public Health Action Plan to Combat 

Antimicrobial Resistance (Part I Domestic Issues).

2

In September 1999, the committee released The use of antibiotics in food-producing 

animals: antibiotic-resistant bacteria in animals and humans.
Appendix IV

Information on Selected Countries’ 

Activities to Address Animal-Related 

Antibiotic Resistance 

Page 75 GAO-04-490 Antibiotic Use in Animals

continued use of the antibiotic on public health. The efficacy assessment 

considers whether the antibiotic is effective in animals for the purpose 

claimed and whether the label contains adequate instructions. As of April 

2003, Australia had completed its assessment of virginiamycin, a member 

of the streptogramin class, and was considering a recommendation to ban 

its use for growth promotion. In addition, as of March 2003, Australia was 

assessing the risk of the macrolide antibiotic class, including tylosin.

Antibiotic resistance surveillance systems. The committee’s 1999 report 

recommended establishing a comprehensive surveillance system to 

monitor antibiotic-resistant bacteria in animals. As of March 2003, a 

strategy for developing an antimicrobial resistance surveillance system was 

being completed. 

Antibiotic use data collection systems. Australia uses import data to 

monitor the annual quantity of antibiotics used in animals because all of the 

antibiotics used in the nation are imported. The data, which include 

information on the quantity of antibiotics imported by antibiotic class and 

end use, are not usually released publicly. A potential problem with this 

data collection method is that importers are not always able to anticipate 

how producers will use the antibiotic. 

Canada Overview of activities. Like the United States, Canada plans to do risk 

assessments of antibiotics important in human medicine and to make 

changes in approved antibiotic uses as appropriate based on these risk 

assessments. Canadian officials expect to initially focus on growth 

promotion uses of several antibiotic classes and antibiotics, including 

penicillins, tetracyclines, tylosin, and virginiamycin. Canada plans to use 

risk assessment methods similar to those used in the United States; 

however, Canada may also consider other factors, such as the benefits 

associated with antibiotic use. In addition, Canada is considering the 

adoption of a prescription requirement for all antibiotic uses in animals 

except growth promotion.

Antibiotic resistance surveillance systems. The Canadian Integrated 

Program for Antimicrobial Resistance Surveillance, started in 2002 and 

designed to use resistance surveillance methods consistent with the United 

States’ NARMS, collects information on antibiotic resistance from the farm 

to the retail levels. Canada issued the first annual report from this 

surveillance system in March 2004.
Appendix IV

Information on Selected Countries’ 

Activities to Address Animal-Related 

Antibiotic Resistance 

Page 76 GAO-04-490 Antibiotic Use in Animals

Antibiotic use data collection systems. Canada is integrating the collection 

of data on antibiotic use in humans and animals into its surveillance system 

and plans to use this information to support risk analysis and policy 

development. Collection of on-farm data on antibiotic use in animals 

through pilot projects is ongoing, and collection of data from 

pharmaceutical companies, importers, and distributors, such as feed mills 

and veterinarians, is planned.

The European Union Overview of activities. In 1999, an EU scientific committee on antibiotic 

resistance recommended that the growth promotion use of antibiotics from 

classes that are or may be used in human medicine be banned. Later that 

year, the EU completed action on this recommendation and banned the use 

of these antibiotics in feed for growth promotion. The scientific committee 

also recommended that the four remaining antibiotics used for growth 

promotion be replaced with other alternatives. In 2003, the EU issued a 

regulation adopting this recommendation, which banned the use of these 

antibiotics as of January 1, 2006.3

 In addition, Denmark, an EU member, 

ended the use of all antibiotics for growth promotion in 2000. 

Antibiotic resistance surveillance systems. Most EU members have a 

program to monitor antibiotic resistance, but the EU as a whole does not 

have a harmonized system that allows comparison of data across nations. A 

November 2003 directive from the European Parliament and the Council of 

the European Union set forth general and specific requirements for 

monitoring antibiotic resistance. Among other things, member countries 

must ensure that the monitoring system includes a representative number 

of isolates of Salmonella spp., Campylobacter jejuni, and Campylobacter 

coli from cattle, swine, and poultry. In particular, Denmark’s surveillance 

system, the Danish Integrated Antimicrobial Resistance Monitoring and 

Research Programme, monitors resistance in these and other bacteria in 

animals, meat, and humans. 

Antibiotic use data collection systems. The EU has proposed that its 

members collect data on antibiotic use in animals. EU countries’ efforts to 

collect this information are at varying stages of development. For example, 

while some EU countries are just developing programs to collect antibiotic 

3

The EU will still allow the use of coccidiostat and histomonostat drugs as feed additives for 

growth promotion. These drugs control parasites and many coccidiostat and histomonostat 

drugs are not used in humans.
Appendix IV

Information on Selected Countries’ 

Activities to Address Animal-Related 

Antibiotic Resistance 

Page 77 GAO-04-490 Antibiotic Use in Animals

use data, the United Kingdom and Denmark currently collect this 

information. 

The United Kingdom’s Veterinary Medicines Directorate collects data from 

veterinary pharmaceutical companies on the amounts of different 

antibiotics and other animal drugs sold in the United Kingdom. The 

directorate then separates these data into chemical groups, administration 

methods, and target species. For certain antibiotics that are sold for use in 

more than one species, it is not possible to determine the species in which 

they were used. However, the directorate is working to more accurately 

assign sales quantities to each species. See table 3 for information on the 

amount of antibiotics sold in the United Kingdom during 2002.

Denmark collects extensive data on the use of antibiotics in animals. In 

particular, through its VetStat program, Danish officials can obtain data on 

all medicines prescribed by veterinarians for use in animals. This program 

provides detailed information on antibiotic use, such as the quantity used, 

class of antibiotic used, species, age of animal, and the purpose of use, as 

well as the disease the antibiotic was used to treat. In addition, VetStat 

allows researchers to calculate the average daily doses that animals receive 

of various antibiotics. See table 3 for information on the amount of 

antibiotics used in Denmark during 2002.

Hong Kong Antibiotic resistance surveillance systems. Hong Kong has an antibiotic 

resistance surveillance system. We did not obtain additional information on 

this system.

Antibiotic use data collection systems. Hong Kong has an antibiotic use 

data collection system. We did not obtain additional information on this 

system.

Japan Overview of activities. Japan is currently reviewing the use of antibiotics 

for growth promotion if those antibiotics are from classes used in humans. 

According to an April 2004 report from the Office of the U.S. Trade 

Representative, the Japanese government has stated that these reviews will 

be based on science. 

Antibiotic resistance surveillance systems. Japan has an antibiotic 

resistance surveillance system. We did not obtain additional information on 

this system.
Appendix IV

Information on Selected Countries’ 

Activities to Address Animal-Related 

Antibiotic Resistance 

Page 78 GAO-04-490 Antibiotic Use in Animals

Antibiotic use data collection systems. Japan has an antibiotic use data 

collection system. We did not obtain additional information on this system.

Mexico Antibiotic resistance surveillance systems. In 2000 and 2001, FDA 

undertook a pilot study with Mexico to monitor the antimicrobial 

resistance of salmonella and E. coli isolates obtained from human samples. 

In September 2001, the pilot study was expanded into a 3-year cooperative 

agreement to include both human and animal monitoring. The primary 

objective of the agreement was to establish an antimicrobial resistance 

monitoring system for foodborne pathogens in Mexico comparable to the 

United States’ NARMS program. 

New Zealand Overview of activities. New Zealand established an Antibiotic Resistance 

Steering Group primarily to coordinate a program to gather and analyze 

information on the use of antibiotics in feed (including antibiotics for 

growth promotion), assist in developing a policy concerning this use, and 

assess the potential transfer of resistant bacteria from animals to humans.4

 

New Zealand has completed its risk assessments of antibiotics for growth 

promotion and no longer allows the growth promotion use of any 

antibiotics that are also related to antibiotics used in human medicine. New 

Zealand did not carry out a comprehensive risk analysis for any of the 

antibiotics being used for growth promotion because the available 

information was not sufficient. Instead, New Zealand used consistent 

rationale, including the mechanisms and potential for antibiotic resistance 

and the potential for that resistance to be transferred from animals to 

humans, in assessing each antibiotic (or class, such as the macrolide class). 

Antibiotic resistance surveillance systems. New Zealand is working to 

implement a comprehensive antibiotic resistance surveillance program. 

According to a January 2003 antibiotic resistance progress report, New 

Zealand has programs to monitor specific pathogens in animals, but the 

programs do not gather information specific to antibiotic resistance. While 

the government informally monitors the antibiotic resistance of E. coli and 

Staphylococcus aureus, the program provides very limited data. 

4

In July 1999, the expert panel released Antibiotic Resistance and In-Feed Use of 

Antibiotics in New Zealand.
Appendix IV

Information on Selected Countries’ 

Activities to Address Animal-Related 

Antibiotic Resistance 

Page 79 GAO-04-490 Antibiotic Use in Animals

Antibiotic use data collection systems. Since 2001, New Zealand has 

collected antibiotic sales data from a formal survey of pharmaceutical 

companies. The companies report the data voluntarily. Annual reports 

provide antibiotics sales statistics by antibiotic class, method of 

administration, type of use (including growth promotion), and animal 

species. The data are only indicative of use because antibiotics are used for 

multiple purposes, and it is impossible to know the exact use of all the 

antibiotics. New Zealand has considered changes to its data collection 

system to provide additional information. See table 3 for information on the 

amount of antibiotics sold in New Zealand during 2002.

South Korea Antibiotic use data collection systems. The Korea Animal Health Products 

Association, an industry group, monitors the quantity of antibiotics 

produced and sold by its members. The data are available on a monthly 

basis and, at a minimum, provide total antibiotic use quantities by species, 

specific antibiotic, and antibiotic class. 
Page 80 GAO-04-490 Antibiotic Use in Animals

Appendix V

Antibiotics Frequently Used in Animals ApendxiV

This appendix provides information available on the antibiotics that are 

frequently used on farms that produce feedlot cattle, swine, and broiler 

chickens in the United States. 

Antibiotic Use in U.S. 

Feedlot Cattle 

Production

In 1999, USDA’s National Animal Health Monitoring System (NAHMS) 

collected data on antibiotic use in beef cattle raised in feedlots. Table 4 lists 

the antibiotics identified as having at least 10 percent of feedlots using 

them in feed or water, or by injection, and the most frequent purpose of 

use, when this information is available. NAHMS provided only limited 

information on how the antibiotics were administered, so this information 

is not included in the table. The table also presents information on FDA’s 

rankings of the importance of the antibiotic class in human medicine. (See 

app. III for further information on FDA’s ranking system.) For those 

antibiotics not found in these rankings, we listed them as not important. In 

particular, over half of the feedlots surveyed used chlortetracycline in feed 

or water,1

 about one-third used tilmicosin to prevent disease, and over half 

used tilmicosin, florfenicol, and tetracyclines to treat disease. In addition, 

about one-third used cephalosporins, fluoroquinolones, and 

penicillins/amoxicillin to treat disease. However, the feedlots using these 

antibiotics do not administer them to all cattle. For example, although 42 

percent of feedlots use antibiotics to prevent respiratory disease, only 10 

percent of feedlot cattle receive antibiotics for this purpose.

1

NAHMS did not specify the purpose of this use, but included the possible purposes of 

disease treatment, disease prevention, and growth promotion.
Appendix V

Antibiotics Frequently Used in Animals 

Page 81 GAO-04-490 Antibiotic Use in Animals

Table 4: Antibiotics Frequently Used in Feedlot Cattle, 1999

Source: GAO analysis of USDA and FDA data.

a

The National Animal Health Monitoring System cited this antibiotic as an example for the class.

b

Used in a combination with chlortetracycline.

Antibiotic Use in U.S. 

Swine Production

In 2000, NAHMS collected data on antibiotic use in swine. Table 5 lists the 

antibiotics identified as those that at least 10 percent of producers use in 

feed or water or by injection for either nursery-age or older swine, the most 

frequent method of administration for these antibiotics, and the most 

frequent purpose of use. The table also presents information on FDA’s 

ranking of the importance of the antibiotic class in human medicine. For 

those antibiotics not found in these rankings, we listed them as not 

important. In particular, about half of the producers surveyed used tylosin 

and chlortetracycline in feed. In addition, about one-third of the producers 

surveyed used a penicillin to treat disease and bacitracin to promote 

growth. However, the producers using these antibiotics do not administer 

them to all of their swine.

Antibiotic class and antibiotic Most frequent purpose of use

Importance of antibiotic class in human 

medicine

Cephalosporin (third generation) Critically important

Ceftiofura Disease treatment

Fluoroquinolone Critically important

Enrofloxacina Disease treatment

Macrolide Critically important

Tilmicosin Disease treatment, disease prevention

Tylosina Disease treatment

Penicillin/Aminopenicillin Highly important

Penicillins/amoxicillin Disease treatment

Phenicol Not important

Florfenicol Disease treatment, disease prevention

Sulfonamide Not important

Sulfamethazineb Not specified

Tetracycline Highly important

Chlortetracycline Not specified

Oxytetracycline Disease treatment, disease prevention
Appendix V

Antibiotics Frequently Used in Animals 

Page 82 GAO-04-490 Antibiotic Use in Animals

Table 5: Antibiotics Frequently Used in Swine, 2000

Source: GAO analysis of USDA and FDA data.

a

A chlortetracycline/penicillin/sulfathiazole combination is used for growth promotion. 

Antibiotic Use in U.S. 

Broiler Production

USDA has not collected any data on antibiotic use in broiler chickens 

through NAHMS. However, a University of Arkansas study used data from a 

corporate database to track patterns of antibiotic use in broiler chickens 

from 1995 through 2000.2

 This study focused on the use of antibiotics in 

Antibiotic class and antibiotic 

Most frequent method of 

administration 

Most frequent purpose of 

use

Importance of antibiotic class 

in human medicine

Cephalosporin (third generation) Critically important

Ceftiofur Injection Disease treatment

Lincosamide Highly important

Lincomycin Injection Disease treatment

Macrolide Critically important

Tylosin Feed, injection Disease treatment, disease 

prevention, growth promotion

Penicillin Highly important

Procaine Penicillin G Injection Disease treatment 

Penicillin Benzathine Injection Disease treatment

Penicillina Feed Growth promotion

Pleuromutilin Not important

Tiamulin Feed Growth promotion

Polypeptide Not important

Bacitracin Feed Growth promotion

Sulfonamide Not important

Sulfathiazolea Feed Growth promotion

Tetracycline Highly important

Chlortetracycline Feed Disease treatment, disease 

prevention, growth 

promotion

Oxytetracycline Injection Disease treatment

Other Not important

Carbadox Feed Growth promotion

2

H.D. Chapman and Z.B. Johnson, “Use of Antibiotics and Roxarsone in Broiler Chickens in 

the USA: Analysis for the Years 1995-2000.” Poultry Science, vol. 81 (2002).
Appendix V

Antibiotics Frequently Used in Animals 

Page 83 GAO-04-490 Antibiotic Use in Animals

feed to promote growth and to prevent disease. Over the period of the 

study, the percentage of production units using antibiotics in feed 

decreased, in part because antibiotics did not prove to be as cost-effective 

as other feed additives that promote growth.3

 The study did not analyze 

data on antibiotics used in chickens for disease treatment. According to 

industry officials, producers seldom treat chickens for diseases.

Table 6 lists the antibiotics identified by the study as being used by at least 

10 percent of broiler production units and their purpose of use. Table 6 also 

presents information on FDA’s ranking of the importance of the antibiotic 

class in human medicine. For those antibiotics not found in these rankings, 

we listed them as not important. 

Table 6: Antibiotics Frequently Used in Feed for Broiler Chickens, 1995-2000

Source: GAO analysis of industry and FDA data.

3

A production unit in most cases represents a broiler complex comprising a group of farms, 

in a common geographical area, that is served by a single feed mill. 

Antibiotic class and 

antibiotic used 

Most frequent purpose

of use

Importance of antibiotic 

class in human medicine

Other Not important

Bambermycin Growth promotion/disease 

prevention

Polypeptide Not important

Bacitracin Growth promotion/ disease 

prevention

Streptogramin Highly important

Virginiamycin Growth promotion/ disease 

prevention
Page 84 GAO-04-490 Antibiotic Use in Animals

Appendix VI

Comments from the U.S. Department of 

Agriculture ApendxiVI

Note: GAO comments 

supplementing those in 

the report text appear 

at the end of this 

appendix.

See comment 1.

See comment 1.

Now on pp. 7 and 41.

See comment 2.
Appendix VI

Comments from the U.S. Department of 

Agriculture 

Page 85 GAO-04-490 Antibiotic Use in Animals

Now on p. 17.

See comment 3.

See comment 4.

See comment 5.

See comment 6.

Now on p. 18.
Appendix VI

Comments from the U.S. Department of 

Agriculture 

Page 86 GAO-04-490 Antibiotic Use in Animals

Now on p. 24.

Now on p. 17.
Appendix VI

Comments from the U.S. Department of 

Agriculture 

Page 87 GAO-04-490 Antibiotic Use in Animals

GAO’s Responses to 

USDA’s Comments

The following are our comments on the USDA letter, dated April 5, 2004.

1. We revised the report to include USDA’s concerns that additional 

funding would be needed to expand CAHFSE.

2. We clarified our discussion of some studies. References are cited in 

footnotes for studies discussed in the report.

3. We agree that the collection of both aggregate and detailed data on 

antibiotic use in animals is useful and that researchers need to know 

specifically how antibiotics are used in order to determine which of the 

uses is responsible for trends in antibiotic resistance. The report 

discusses both aggregate and detailed data. As USDA states, the report 

highlights the CAHFSE program, through which USDA is collecting 

specific, on-farm data on swine. In addition, the report discusses 

Denmark’s system, which collects detailed data on how antibiotics are 

used in animals.

4. We found that only a few studies have concluded that the risk is 

minimal, while many studies have concluded that there is a significant 

human health risk from the transference.

5. We revised the report to include information on research funded by 

USDA’s Cooperative State Research, Education, and Extension Service.

6. We clarified the report to reflect comments on specific studies. In 

addition, we clarified the report to indicate which results were from 

epidemiologic studies alone, and which results were from 

epidemiologic studies that included molecular subtyping techniques.
Page 88 GAO-04-490 Antibiotic Use in Animals

Appendix VII

Comments from the Department of Health and 

Human Services ApendxiVI
Appendix VII

Comments from the Department of Health 

and Human Services 

Page 89 GAO-04-490 Antibiotic Use in Animals
Appendix VII

Comments from the Department of Health 

and Human Services 

Page 90 GAO-04-490 Antibiotic Use in Animals
Appendix VII

Comments from the Department of Health 

and Human Services 

Page 91 GAO-04-490 Antibiotic Use in Animals
Appendix VII

Comments from the Department of Health 

and Human Services 

Page 92 GAO-04-490 Antibiotic Use in Animals
Appendix VII

Comments from the Department of Health 

and Human Services 

Page 93 GAO-04-490 Antibiotic Use in Animals
Appendix VII

Comments from the Department of Health 

and Human Services 

Page 94 GAO-04-490 Antibiotic Use in Animals
Page 95 GAO-04-490 Antibiotic Use in Animals

Appendix VIII

GAO Contacts and Staff Acknowledgments ApendxiVI

GAO Contacts Martin T. Gahart, (202) 512-3596

J. Erin Lansburgh, (202) 512-3017

Acknowledgments In addition to those named above, Gary Brown, Diane Berry Caves, Diana 

Cheng, Barbara El Osta, Ernie Jackson, Julian Klazkin, Carolyn Feis 

Korman, Deborah J. Miller, Sudip Mukherjee, Lynn Musser, Roseanne Price, 

and Carol Herrnstadt Shulman made key contributions to this report.

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