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The Use of Drugs in Food Animals: Benefits and Risks (1999)

Chapter: 2 Food-Animal Production Practices and Drug Use

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Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
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2
Food-Animal Production Practices and Drug Use

OVERVIEW

Food-animal production has intensified over the past 50 years. The number of livestock and poultry farms in the United States has decreased, but the density of animals on those farms has increased substantially. Production also has become more efficient; a greater quantity of commodities is produced by fewer animals. The increase in efficiency results from several factors, including preventive medicine, genetic selection, and improved nutrition and management. Veterinary medical care in food animals consists of the use of: (1) vaccines and prophylactic medication to prevent or minimize infection; (2) antibiotics and parasiticides to treat active infection or prevent disease onset in situations that induce high susceptibility; and (3) antibiotic drugs and hormones for production enhancement, growth promotion, and improved feed efficiency. This chapter provides a historical description of the major food-animal industries, the challenges faced by each that influence drug use today, and the types of drugs in use and the trends associated with food-animal production. It might appear that some of the data presented are unbalanced with regard to the quantity of information presented and the inferences made regarding health statistics and antibiotic drug use. The imbalance largely reflects the availability of data from quality-assurance programs and feeding and production records.

The structure of the major food-animal industries varies considerably, and this variation has an important influence on accountability (the recorded instances of use, duration, procurement records, containment, security, and appropriateness of use) for use of drugs and the ease of implementing quality-assur-

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

ance programs within individual industries. The structure of the industries also affects the ease of identifying the source of a problem (whether it is a pathogenic microorganism, a drug residue, or an antibiotic-resistant bacteria) and the ease with which consumer preferences flow back through the system to stimulate changes in the genetics and breeding of stock to produce the desired product.

In all of the animal industries, antibiotic drugs are used for three primary reasons: (1) therapeutically, for treating existing disease conditions; (2) prophylactically, at subtherapeutic concentrations1; and (3) subtherapeutically for production enhancement (increased growth rate and efficiency of feed use). Therapeutic use generally occurs after diagnosis of a disease condition, and treatment is governed by the drug’s label instructions or in accordance with extra-label instructions provided by a veterinarian in the context of a valid and current veterinarian–client–patient relationship (VCPR). Subtherapeutic doses are used when pathogens are known to be present in the environment or when animals encounter a high-stress situation and are more susceptible to pathogens. Subtherapeutic doses are smaller than those required to treat established infections. They might also use compounds developed exclusively as production enhancers that have no therapeutic purpose. Although the U.S. Food and Drug Administration (FDA) defines subtherapeutic concentration as <200 g/t of feed, there is a wide range of concentrations below that for which different antibiotics are formulated into feeds and fed to different species.

As summarized in Cromwell (1991), there are three mechanisms of action through which antibiotics appear to enhance growth and production. The first involves direct biochemical events that are affected by antibiotics: nitrogen excretion, efficiency of phosphorylation reactions in cells, and direct effects on protein synthesis. The second involves direct effects on metabolism, including the effects of antibiotics on the generation of essential vitamins and cofactors by intestinal microbes and the way that antibiotics affect the population of microbes that make these nutrients. In addition, the feeding of antibiotics is associated with decreases in gut mass, increased intestinal absorption of nutrients, and energy sparing. This results in a reduction in the nutrient cost for maintenance, so that a larger portion of consumed nutrients can be used for growth and production, thereby improving the efficiency of nutrient use for productive functions. The third proposed mechanism of action is eliminating subclinical populations of pathogenic microorganisms. The elimination of this route of metabolic drain allows more efficient use of nutrients for production.

The goal of an efficient livestock operation is to maintain animals that are free of disease or injury, that gain weight well if they are intended for market, or that stay in optimal condition if they are kept as breeding stock. The producer

1  

Antibiotics are used in food animals therapeutically to treat disease and sub-therapeutically (at <200 g/t of feed) to increase production performance, to increase efficiency in the use of feed for growth or output, and to modify the nutrient composition of an animal product.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

relies on many methods of disease prevention and treatment. The worst case is having diseased and injured animals deprived of therapeutic treatment. Such a situation results in needless pain and suffering and, in far too many cases, in death. Leaving sickness or injury untreated is the most expensive alternative for the owner and is certainly the least humane for the animal.

The strategies for raising food animals are pertinent to the larger issue of human health effects from drug use in food animals. The intensiveness of farm production in this country has increased because of the advantages inherent in the use of drugs that prevent or control infection and promote growth in animals. Strong incentives for the use of these drugs exist to assure the public that only healthy animals enter the food chain and to maintain the profitability of the industry.

A significant limit to animal production efficiency is any form of disease stress that animals might encounter in their production lives. Traditional growth promoters, such as the steroidal and nonsteroidal estrogenic agents, are less effective when used, because even low-grade disease affects general metabolism. For this reason, pharmacological strategies to prevent or treat animal diseases are used, and the drugs of choice for bacterial infections are antibiotics. Adequate use of antibiotics is necessary for several reasons. Improvements in feed efficiency reduce environmental pollution, for example, through reduced nitrogen and phosphorus losses in animal waste products. Illness in herds and flocks decreases production and nutritional use efficiency (Elsasser et al. 1995, 1997). Klasing and co-workers (1987) suggested that the antigenic challenge of the immune system in animals fighting off disease stress and illness causes repartitioning of nutrients away from growth and production to support the mechanisms that participate in restoring homeostasis and health. Repartitioning of nutrients is a process in which hormone and immune cytokines direct one type of cell to not take up and use a given nutrient and to spare the availability of that nutrient while facilitating other cells (e.g., immune function cells) in increasing their metabolism and uptake of nutrients (Elsasser et al. 1995).

THE POULTRY INDUSTRY

Originating in the 1700s, the U.S. poultry industry grew in size and genetic diversity as chickens were brought to North America on ships from Europe and Asia. In the 1870s, farmers began to select breeding stock, emphasizing specific traits pertaining to meat and egg production. Bugos (1992) outlined the evolution of the broiler and egg-layer industries and the breeding that propelled rapid advances in each. In 1928, before modern breeding began for broilers, the average broiler required 112 days and 22 kg of feed to reach a 1.7-kg market weight. By 1990, broilers required 42 days and less than 4 kg of feed to reach a market weight of 2.0 kg. Laying hens produced an average of 93 eggs per year in 1930, 174 eggs per year in 1950, and 252 eggs per year in 1993. Immediately after

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

World War II, the broiler industry was concentrated in the northeastern and the midwestern states. However, by 1991, 54 percent of broilers were produced in just four states: Arkansas (16 percent), Georgia (15 percent), Alabama (14 percent), and North Carolina (9 percent) (Knutson 1993). Broiler production in the United States increased from 1.6 billion birds in 1960 to 7.0 billion birds in 1994, a number that corresponds to 13.6 billion kg (30 billion lb) of meat with a value of $10 billion (FSIS 1994b). Annual per capita consumption of poultry meat (chicken and turkey) was projected to be 43 kg (94 lb) in 1995. Similarly, egg production in the United States has grown from 59 million eggs produced in 1950 to 70 million eggs produced in 1994, with average consumption projected to be 240 eggs per capita in 1995. Selective breeding has propelled the poultry industry and allowed the breeders to become relatively independent; at the same time, broiler, layer, and turkey industries have become integrated (Rogers 1993).

An Integrated Industry

Integration is defined as the unified control of several successive (vertical) or similar (horizontal) economic, especially industrial, processes formerly carried out independently. When that definition is applied to the various animal industries, it is notable that the poultry industry is vertically integrated with the exception of the primary breeders who produce the parent strains for commercial production. The swine industry is progressing rapidly toward complete vertical integration. The dairy industry, by its very nature, involves some degree of vertical integration, and the beef and sheep industries remain largely unintegrated. Some effort has been made, starting with the processors, to integrate beef cattle production, but in general the various segments of these industries continue to operate independently.

In vertical integration, the integrator (the poultry company) buys the breeder’s eggs that become the parent stock of the broilers and delivers the hatched broiler chicks to others who are under contract to grow the birds, usually in floor pens with 10,000 to 20,000 birds per pen (Lasley 1983). Turkeys are bred and managed similarly to broilers, except that pens of 5,000 to 10,000 birds are more common (Lasley et al. 1983). The integrator maintains ownership of the birds, and supplies the feed and medication to the grower. Integrators also own their feed mills (to control costs and customize feed) where the grain can be purchased in bulk at cost savings to the grower–producer. In addition, integrators own the slaughter and processing facilities, and they generally market the finished product.

Poultry diets, which constitute 68 percent of total production costs, consist of corn and soybean-meal mixtures with vitamins and minerals, and typically include two or three medications (North 1984). Starter, grower, finisher, and layer diets are designed to meet the needs of the birds in each phase of development.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

Medications and vaccinations make up 2.16 percent of the total production costs (Agrimetrics Associates 1994).

History and Trends in Drug Use

The growth-enhancing effect of antibiotics was first demonstrated for poultry. Various nutritional studies in chicks showed that antibiotic-fermentation products influenced the growth of chicks (Moore et al. 1946; Stokstad et al. 1949). By 1951, the addition of growth-promoting antibiotics to feed had become standard practice (CAST 1981). The history of antibiotics, growth-promotion compounds, arsenical compounds, and coccidiostats has been reviewed (NAS 1969; Fagerberg and Quarles 1979; CAST 1981; IOM 1989). An earlier review of poultry experiments showed an important advantage in the use of low concentrations of various antibiotics (NAS 1969) that was evident in the superior growth of birds that received antibiotics. The majority of drug use in poultry management practice today is prophylactic, with the bulk of medications encompassing application of antiprotozoal compounds and antibiotic growth promoters.

The poultry production system serves as an interface between animal and human health and affects the environment, so it is important to describe drug use in the context of the overall system as well as to define what process controls are in place to address the safety and quality of the products. In terms of the overall system, intensive management and confinement operations minimize some kinds of infection and facilitate control of others. For example, Salmonella gallinarum and Salmonella pullorum, which are spread congenitally through the fertilized egg, are controlled by using breeding birds that test negative. Tuberculosis has been virtually eliminated by culling from the flock birds that test positive.

Calnek et al. (1991) assembled a comprehensive treatise on diseases of poultry. Vaccination of day-old chickens controls some viral infections, such as Newcastle and Marek’s diseases. Turkeys are routinely vaccinated against Newcastle (5 days of age) and hemorrhagic enteritis (2 to 3 weeks of age), and sometimes against erysipelas, Bordetella avium, cholera, and influenza, depending on local experience. Antibacterials and other chemicals are frequently used for controlling other infections such as coccidia, worms, fungi, ectoparasites, and several bacterial infections.

In practice, broiler producers almost always include a coccidiostat (Table 2–1) in grower rations, as well as an arsenical, and an antibiotic (Table 2–2) for improved feed efficiency and body weight gains and for reduced morbidity and mortality. Control of coccidiosis is imperative with modern management systems for broilers and turkeys. Table 2–1 lists 20 coccidiostats labeled for use in broilers (Shepard et al. 1992), 11 of which also may be used in turkeys; only 2 are approved for layer chickens. The ionophores dominate the coccidiostats, but evolution of resistant coccidia has led many broiler producers to alternate

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–1 Coccidiostats Approved for Use in Broilers (B), Turkeys (T), and Layers (L)

Sulfonamides

Ionophores

Others

Sulfachloropyrazine (B)

Lasalocid (B)

Amprolium (B, T)

Sulfamethazine (B, T)

Maduramycin (B)

Arsanilate (B, T, L)

Sulfadimethoxine (B, T)

Monensin (B, T)

Buquinolate (B, L)

Sulfamyxin (B, T)

Narasin (B, T)

Clopindol (B, T)

Sulfanitran (B)

Salinomycin (B, T)

Dequinate (B)

Sulfaquinoxaline (B, T)

 

Nequinate (B)

 

 

Nicarbazin (B)

 

 

Robenidine (B)

 

 

Zoalene (B, T)

 

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

TABLE 2–2 Major Claims of Antibiotics Approved for Use in Chickens and Turkeys

Compound

Growth and Feed Efficiency

Various Infections

Bambermycin

yes

no

Bacitracina

yes

yes

Chlortetracycline

yes

yes

Erythromycina

no

yes

Gentamycin

no

yes

Neomycin

no

yes

Novobiocin

no

yes

Oleandomycin

yes

yes

Oxytetracyclinea

no

yes

Penicillin

yes

yes

Roxarsone

yes

yes

Spectinomycin

yes

yes

Streptomycin

no

yes

Tetracycline

no

yes

Tylosina

yes

yes

Virginiamycin

yes

yes

Fluoroquinolones

no

yes

aAlso labeled for use in layer chickens.

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

coccidostats in “shuttle” programs. Several turkey farms now use a coccidiosis vaccine with good results.

All of the antibiotics listed in Table 2–2 are marketed over the counter. Several of these antibacterials are labeled for use against some other specific infections, but some viral infections still periodically devastate the industry. For example, in extreme cases of avian influenza, houses can be depopulated and sanitized to eradicate the virus. Mycoplasma galisepticum and Mycoplasma synovia were ubiquitous and required prophylaxis in broilers, for example, with tylosin or oxytetracycline. On the other hand, mycoplasmas have been controlled in most turkey flocks by using breeders that test negative. According to Shepard et al. (1992), 16 antibiotics are approved for use in broilers or turkeys (Table 2–2), but only 4 of these may be used in layers. In addition, 2 arsenicals are approved for control of blackhead, 4 compounds are available for worms, and 1 fungicide is approved for broilers.

There are three categories of antiprotozoal drugs: ionophores, sulfonamides, and other chemical compounds. They are routinely administered through feed. Some ionophores are not well absorbed across the intestinal wall or are not sufficiently toxic to dictate a withdrawal period and so they can legally be used until slaughter. (Withdrawal is the period required by law between the final administration of a drug and the time when the animal can be harvested for food. The withdrawal period allows drug residue concentrations to fall in the tissue or milk of treated animals to those considered nonthreatening to human health.) Chemical coccidiostats (e.g., amprolium, roxarsone) are most often used in broiler starter diets and traditionally have been followed by ionophores. Most chemical coccidiostats require withdrawal periods.

Antiprotozoal drugs used to combat Histomonas infections in turkeys and pheasants are similar to the organic arsenical compounds used in broiler chickens. Nitrarsone (4-nitrophenyl arsenic acid) is the only compound approved to prevent histomoniasis and the subsequent sequella produced by the protozoa in combination with some bacteria. Two other compounds previously approved for this purpose, ipronidazole and furazolidone, were recently removed from the market. Furazolidone is a member of the nitrofuran family of compounds, which were removed from the market by the FDA’s Center for Veterinary Medicine because of their carcinogenic potential; however, similar compounds are still in use in human medicine today.

The integration of the poultry industry facilitates tracing a potential residue in meat or eggs to its origin. The integrator companies have much to gain by avoiding altogether any hint of problems, such as drug residues in poultry foods. This constitutes a powerful motivation to control drug and chemical use.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

Routes of Drug Administration

Feed

Several diet formulations are typically fed to poultry from hatching to market. Prestarter and starter diets are fed to broilers for up to 19 days after hatching. These diets might contain up to three drug components: (1) a prophylactic coccidiostat, (2) a growth-promoter antibiotic, and (3) an organic arsenical compound that has both growth promoter and coccidiostat activity. A battery of grower diets are fed for the next 8 to 12 days to maintain the metabolic requirements of these fast-growing birds, and withdrawal diets of one or two types are fed in the remaining days before market. Thus, the diets used in each phase are progressively reduced in drug use and cost. To comply with FDA-mandated drug-withdrawal periods, organic arsenical compounds are not used in withdrawal diets.

Most poultry operations routinely monitor withdrawal feed to ensure compliance, for several reasons. First and foremost, monitoring reduces any potential risk that drug residues will remain in tissues, and second, the difference in cost between withdrawal diets and grower diets is substantial. The cost differences might exceed $20/t; if grower feed were fed in place of withdrawal feed, the cost of gain would increase. The industry has adopted what is known as a “two-bin system” for most broiler houses. This system places two bulk tanks at each grower’s house and eliminates mixing of withdrawal feed with other types. Further monitoring by tissue analyses is done before slaughter. Fat and other samples are tested for residues of pesticides, herbicides, and heavy metals.

One-Day-of-Age Injection

Two drugs are currently approved (ceftiofur sodium and gentamicin sulfate) for one-day-of-age injection of chicks. Neither drug is absorbed gastrointestinally. Both have been used to protect the poult or chick from injection-site abscesses after vaccination for Marek’s disease. Because mass incubation and hatching techniques create significant challenges with aerosols of various genera of Enterobacteriaceae, one-day-of-age injections can be used to improve early viability.

Water Medication

Sick poultry are generally medicated through drinking-water systems. Systemic or intestinal medication can be given that way, and the industry has learned how to achieve and maintain therapeutic concentrations of drugs by studying the actual water use for each class of poultry, and accounting for the age of the birds and the environmental temperature. Although the actual overall water-soluble

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

systemic use of drugs in poultry is declining, a recently approved therapeutic-concentration fluoroquinolone antibiotic may now be administered to poultry via drinking water. Summaries of drug use in poultry from 1989 to 1994 are presented in Tables 2–3, 2–4, and 2–5. The amount of antibiotics administered to poultry, especially the amount administered in medicated feeds, declined for the following reasons:

  • use of preventive medicine, including implementation of biosecurity procedures, vaccination, genetic selection, and eradication of various pathogens, resulting in specific-pathogen-free stocks;

  • reduction in the number of available efficacious compounds for treating respiratory diseases caused by Escherichia coli and Pasteurella multocida, and for treating other infections such as those caused by Staphylococcus aureus;

  • efforts to control cost, including improving environmental conditions and culling unhealthy birds;

  • concentration and focus on residue avoidance; and

  • innovation on the part of manufacturers of vaccines and biological agents to rapidly meet the demands of industry when exotic diseases occur.

These reasons notwithstanding, there is cause for concern in the poultry industry. In recent years only one new systemic antibiotic, a fluoroquinolone, has been approved for treatment of diseases caused in poultry by E. coli. The use of that antibiotic is being criticized because its effectiveness as a last line of defense in human antibiotic therapy might be undermined by further FDA approval and use in animals. The removal of the nitrofurans from the market further complicated the situation. When exotic or variant respiratory viruses emerge in an area, septicemic E. coli infections cause excessive mortality if no treatment is initiated. In the past, vaccine strategies were developed and implemented to prevent the spread of the newly emerged virus and to decrease the stresses on poultry that facilitate opportunistic secondary bacterial infection such as occurs with E. coli.

TABLE 2–3 Cost of Drug and Vaccine Use in Broilers from 1989 to 1994

Treatment

1989

1990

1991

1992

1993

1994

Vaccine (¢/broiler)

0.14

0.15

0.14

0.14

0.13

0.14

Direct medication (¢/broiler)

0.09

0.09

0.07

0.06

0.05

0.06

Feed medication (¢/broiler)

0.58

0.68

0.60

0.56

0.56

0.52

Total (¢/broiler)

0.81

0.92

0.81

0.76

0.74

0.72

Diseased or condemned (%)

1.01

0.96

0.80

0.85

0.67

0.81

 

Source: Agrimetrics Associates, Inc., 1994.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–4 Turkey Medication and Vaccine Cost Analysis

Treatment

1st Half 1989

1990

1991

1992

1993

1994

Confined hens

 

Feed medication ($/t of feed)

2.91

2.93

3.14

3.09

3.171

3.22

Feed conversion (lb feed/lb weight gain)

2.401

2.400

2.380

2.448

2.471

2.397

Field medication and vaccine ($/lb)

0.0038

0.0032

0.0035

0.0034

0.0031

0.0035

Feed medication ($/lb)

0.0035

0.0035

0.0037

0.0038

0.0039

0.0039

Confined toms

 

Feed medication ($/t of feed)

2.62

2.85

1.64

3.17

3.21

3.03

Feed conversion (lb feed/lb weight gain)

2.686

2.660

2.582

2.579

2.583

2.667

Field medication and vaccine ($/lb)

0.0043

0.0039

0.0035

0.0036

0.0034

0.0035

Feed medication ($/lb)

0.0035

0.0038

0.0021

0.0041

0.0041

0.0040

 

Source: Agrimetrics Associates, Inc., 1994.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–5 Cost of Medication and Vaccination Used for Turkeys and Broilers in the United States

 

Medicationa

Vaccinationb

Target Use

Total Live Cost (¢/lb live weight)

Cost (¢/lb live weight)

Percentage of Total Live Cost

Cost (¢/lb live weight)

Percentage of Total Live Cost

Hen turkey

32

0.165

0.52

0.083

0.26

Tom turkey

26

0.231

0.64

0.116

0.32

Broiler

c

0.060

0.22

0.140

0.50

aWater-soluble medication only, excluding feed-grade drugs.

bVaccines and vaccine stabilizers.

cTotal live cost for chicken amounts to 28 ¢/lb live weight.

Source: Agrimetrics Associates, Inc., 1994.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

Growth Promotion

The poultry industry no longer uses low concentrations of tetracyclines, penicillin, or tylosin for growth promotion. Arsenical compounds are still used as partial coccidiostats and growth promoters. The primary reason for the use of nonsystemic growth promoters is for specific activity against clostridial species. The current practices of drug use for growth promotion in poultry are (1) use of low concentrations, 1 to 50 g/t; (2) routine use; (3) use of minimally or nonabsorbed drugs; (4) use of antibiotics having activity against Gram-positive organisms; and (5) use of nontherapeutic drugs. These drugs include bacitracins, bambermycins, lincomycin, and virginiamycin. All four of these drugs are classified by FDA as category I drugs, requiring no withdrawal period (Feed Additive Compendium 1995).

Disease Control

The three most serious bacterial diseases in poultry are caused by Salmonella, E. coli, and Clostridium. All have human health implications and highlight the need for safe and effective drugs to control these pathogens in birds as well as for the development of vaccination strategies to prevent clinical infection by pathogens (Cooper et al. 1994).

Salmonella Control

Salmonella infections are a persistent worldwide problem (Houston 1985). The total economic impact of human nontyphoid, foodborne salmonellosis in the United States is estimated to range from $0.6 billion to $3.5 billion annually (ERS 1996b). Efforts to control the spread of Salmonella do not have the same momentum in the United States as in Europe. One reason is that more cases of human salmonellosis are reported in Europe than in the United States. About 3 cases per 100,000 population occur in the United States, and at last report, 262 cases per 100,000 occur in Germany. The reasons for the difference are not the subject of this report, but some can be related to food-handling differences and the strains of Salmonella that have emerged to infect the human population.

Salmonella control in poultry is a growing concern today, principally because better detection and screening methods are establishing the magnitude of the problem. Also, recent increases in the virulence and in the pathogenicity of many Salmonella strains make infections with these bacteria more difficult to control. Official USDA statistics have documented a Salmonella-positive broiler carcass percentage rate between 35 and 75. The rate of positives varies by year within the same geographic region and the same processing plant. One major poultry integrator studied 328,000 cultures of Salmonella from one processing plant in North Carolina over a 17-year period. The results suggest that cumula-

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

tive annual rainfall is positively correlated with the incidence of the carcasses, testing positive for Salmonella (Colwell and Brooks 1994). The results are supported by the work of Opara et al. (1992) who studied water activity of the litter. On dirt-floor broiler housing, higher water activity of the litter correlates positively with a higher incidence of Salmonella contamination. With careful processing techniques and chlorine rinses, some broiler integrators can achieve as low as a 6 to 8 percent positive incidence of Salmonella. In addition, data have been gathered by several large poultry integrators to show that Salmonella-positive flocks are more expensive to raise (Bender and Mallinson 1991).

Escherichia coli Control

E. coli infection in poultry is among the most costly diseases to challenge the industry. The majority of American poultry isolates of E. coli are resistant to most if not all of the U.S.-approved poultry chemotherapeutic agents (Raemdonck et al. 1992). The same is true of isolates from Morocco (Filali et al. 1988). Turkeys are equally affected with Pasteurella multocida (Walser and Davis 1975) and E. coli (Glisson, J. R. 1995. University of Georgia, Athens, personal communication). It has been estimated that 2 to 4 percent of all turkey production losses are due to E. coli (Miles and Barnes 1995). Competitive exclusion products (cultures of live mixed populations of normal gut flora that competitively outgrow some undesirable bacteria and, therefore, aid in controlling enteric pathogens) appear to control E. coli pathotypes found in poultry (Weinack et al. 1981; Soerjadi et al. 1981). However, they do not inhibit the nonpathogenic commensal E. coli present in normal gut flora.

Clostridium Control

Clostridia frequently overgrow normal intestinal flora after infections with the coccidiosis parasite, Eimeria. Clostridial infections produce toxins that kill poultry at minimal doses. Coccidiostats are routinely used as prophylactic medication to prevent clinical diseases. Competitive exclusion products appear to control Clostridium if the coccidia control is reasonable (Dekich, M. A. 1995. Perdue Farms, Inc., personal communication). Clostridium species resistant to bacitracins are emerging in several areas in the United States. Twenty-six isolates of Clostridium perfringens were made from poultry in necrotic enteritis outbreaks, and the minimal inhibitory concentration (the concentration of an antibiotic that arrest the growth of a particular organism) was determined for bacitracins, lincomycin, virginiamycin, and penicillin. Preliminary data collected by Cummings et al. (1995) were interpreted by those authors to suggest a trend of increasing resistance to bacitracins and lincomycin in the Clostridium perfringens isolates. Most isolates showed sensitivity only to virginiamycin and penicillin. Probiotic organisms such as Lactobacillus spp. are efficacious under

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

specific conditions. Those conditions include monocultured birds challenged with Clostridium perfringens (Fukata et al. 1991).

In the future, much of the effort to control pathogens in food animals, including poultry, will depend on the increased use of vaccination programs. Advances in molecular biology will permit specific pathogen antigens to be cloned and synthesized, facilitating their use in vaccines to stimulate the animal’s own natural defense mechanisms.

THE SWINE INDUSTRY

In 1900, approximately 90 percent of U.S. farms maintained hogs. That percentage fell to 25 percent in 1969 (Hayenga et al. 1985). More than 3 million farms had hogs in 1950, but fewer than 250,000 had hogs in 1992 (NPPC 1994), and fewer than 100,000 are expected by the year 2000 (Hurt et al. 1992). However, the total number of hogs slaughtered in the United States has remained relatively constant, fluctuating between 1950 and 1992 from a low of 70 million (1975) to a high of 97 million (1980). Fewer farms are producing about the same number and total weight of hogs to meet consumer demands of 8 billion kg (17 billion lb) of total pork, or 31 kg (68 lb) of pork per capita, annually.

Substitution of capital for labor was the major force that led to fewer, larger, and more specialized farms. From the standpoint of economics, larger swine farms run more efficiently than do smaller units. Farms with 10,000 hogs enjoy nearly one-third greater efficiency than do those with 3,000 (Hurt et al. 1992).

Eight major breeds contribute to the U.S. hog herd, but marketed hogs are the result of crossbreeding in an effort to capture the best traits from each breed and some heterosis as well (Fredeen and Harmon 1983; NPPC 1994). Heterosis is the beneficial result of animal crosses in breeding to increase disease resistance, growth characteristics, and other physical qualities. Multinational companies offer genetically consistent hogs that produce more lean pork on less feed. Consumer preferences are relayed effectively through the pork processors to the producers on specialized farms, which now produce nearly identical animals delivered to slaughter. Slaughter facilities are now located near the hog farms and have started to move regionally from their traditional location in the Midwest to the Southeast. Iowa is still ranked first in swine production (approximately 25 percent of the market); North Carolina is now ranked second (13 percent) (ERS 1996a).

Marketing of hogs is changing from open markets, where farmers sell hogs to the highest bidder and where the quality of the hog has little effect on price, to contracts by which processors pay farmers a fee plus performance incentives to feed hogs to market weight (Barkema and Cook 1993). To achieve even greater control, a few processors raise and feed their own hogs in a vertically integrated production system similar to that for broiler chickens. These structural changes now in progress in the pork industry have profound implications. The processor

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

will be more sensitive than is a more distant producer to the potential ramifications of drug residues in pork, and tracing a residue to its origin will be facilitated by contracts and integration. Lifetime identification of food animals was recommended previously to facilitate tracing contaminations to their origins (NRC 1985).

Although some farrowings (the process of birthing piglets) are still in small houses on pastures, about 80 percent are in confinement (FSIS 1992) to better manage the environment, and the vast majority are in farrowing crates to optimize survival of the piglets. Commonly, after farrowings the farrowing house is emptied, pressure cleaned with hot water, and disinfected to minimize subsequent infections and optimize productivity. Pigs are weaned at 3 to 5 weeks of age to maximize the number of piglets born per sow per year. Research continues on ways to reduce the age at weaning to as little as 5 to 6 days to control more effectively several of the major infectious diseases of sows and piglets (Dial et al. 1992). Such control involves antibiotic medication of the sows before farrowing and the piglets until after weaning.

In the various management systems, weaned pigs might be moved to a nursery, a grower, or a feeder–finisher facility. Although more than three-fourths of the hogs are produced on “farrowtofinish” farms (FSIS 1992), some producers sell feeder pigs at 8 to 9 weeks of age (about 23 kg [50 lb] of body weight) for finishing on other specialized farms. Market hogs weigh about 114 kg (250 lb) at 4.5 to 6.5 months of age (NPPC 1994).

Disease Control and Use of Drugs and Chemicals

Pork producers and herd veterinarians view human food safety as an integral part of total herd health programs. Producers pay strict attention to the health of their herds, taking precautions and using a variety of management practices to protect herd health. Individual herd health programs are developed in close consultation with veterinarians.

Antibiotic drugs are used in pork production for disease prevention, treatment of disease, and growth promotion. The management system in place for individual swine production operations will determine the antibiotic used and the quantity.

In the extensive management of hogs until after World War II, common diseases, such as erysipelas and cholera, were controlled by vaccinations, slaughter, or treatment of individual hogs (Fredeen and Harmon 1983). Epidemics of the common infectious diseases were kept in check by stocking with low-density population. However, in the intensive management of common diseases today hogs usually are given subtherapeutic concentrations of antibiotic drugs in feed. Shepard et al. (1992) listed 29 antibiotic drugs approved by FDA (21 antibiotics and 8 chemotherapeutics).

Thus, in addition to antibiotics, antiparasitics are another major category

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–6 Major Claims of Antibiotics Approved for Use in Hogs

Compound

Growth and Feed Efficiency

Various Infections

Amoxicillina,b

no

yes

Ampicillina,b

no

yes

Apramycin

no

yes

Arsenilic acid

yes

yes

Bacitracin

yes

yes

Bambermycins

yes

no

Chlortetracycline

yes

yes

Efrotomycin

yes

no

Erythromycin

no

yes

Gentamycin

no

yes

Lincomycin

no

yes

Neomycin

no

yes

Oleandomycin

yes

no

Oxytetracycline

no

yes

Penicillin

yes

no

Spectinomycin

no

yes

Streptomycin

no

yes

Tetracycline

no

yes

Tiamulin

yes

yes

Tylosin

yes

yes

Virginiamycin

yes

no

aOnly in combination with chlortetracycline and penicillin.

bAvailable by prescription only.

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

of drugs for hogs. Nine chemical entities are approved in the United States (Shepard et al. 1992), several marketed by more than one company and in forms suitable for use in feed or by injection. They are recommended routinely for breeding animals, when new animals are introduced into a herd, and when weaned animals enter the feedlot. Controlling helminths is the principal objective, but insects also must be controlled. In general, although parasites can severely restrict productivity in hogs, several bacterial and viral infections are more cataclysmic (see Tables 2–6 and 2–7).

Growth and Metabolic Performance

Hog performance (growth rate and feed efficiency [pounds of feed consumed for a gain of 1 pound in carcass or body weight]) is improved with the use of subtherapeutic concentrations of any of 12 antibiotic drugs with claims for

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–7 Major Claims of Chemotherapeutics Approved for Use in Hogs

Compound

Growth and Feed Efficiency

Various Infections

Arsanilate sodium

no

yes

Arsanilic acid

yes

yes

Carbadox

yes

yes

Roxarsone

no

yes

Sulfaethoxypyridazinea,b

no

yes

Sulfachlorpyidazine

no

yes

Sulfamethazine

no

yes

Sulfathiazolea

no

yes

aOnly in combination with chlortetracyline and penicillin.

bAvailable by prescription only.

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

increased rate of gain or improved feed conversion. An important result of subtherapeutic use is reduced morbidity and mortality in growing pigs (Cromwell 1991). In breeding animals, feed-additive antibiotic drugs improve farrowing rate, litter size, birth weight, and pigs weaned per litter; and they reduce the incidence of mastitis (bacterial infection of the mammary gland), metritis, and agalactia. It is not surprising, therefore, that antibiotic drugs are used in about 90 percent of starter feeds, in 75 percent of grower feeds, in more than 50 percent of finisher feeds, and in at least 20 percent of sow feeds (Cromwell 1991). Although antibiotic resistance emerges in herds medicated continuously (Tribble 1991), the procedure does not seem to diminish the enhanced productivity effects (Cromwell 1991).

In swine production today, producers vaccinate piglets for some or all of the following diseases or microbes: erysipelas (46 percent), atrophic rhinitis (42 percent), Pasteurella pneumonia (28 percent), Haemophilus pleuropneumonia (13 percent), Streptococcus infections (12 percent), E. coli scours, and C. perfringens infections (FSIS 1993a). The piglets are castrated by the age of weaning (90 percent), given iron supplements and have tails docked (80 percent), treated for worms (48 percent), treated for mange and lice (40 percent), and given antibiotic injections (33 percent). Among sows and gilts, 60 to 70 percent are vaccinated for leptospirosis, parvovirus, and erysipelas; 50 percent for E. coli scours; 33 percent for atrophic rhinitis; and more than 20 percent for transmissible gastroenteritis, C. perfringens infections, and pseudorabies (FSIS 1992). Eighty-five percent of sows and gilts are wormed, and 72 percent are treated for mange and lice.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

THE DAIRY INDUSTRY

Milk cows were brought to the United States in the 1600s. The dairy industry has changed considerably since then. In 1910, more than 20 million cows were maintained on 5 million farms, averaging 4 cows per farm. In 1993, a total of 9.6 million dairy cows were on 159,450 farms (FSIS 1994b). Yet production of dairy products has increased substantially. Milk production increased from 61 million kg (135 million lb) in 1984 to 70 million kg (154 million lb) in 1994, while the total number of milk cows decreased by approximately 1.2 million. Milk production increased from 5,598 kg (12,316 lb) per cow in 1983 to 7,478 kg (16,451 lb) per cow in 1995 (ERS 1996a).

Consumers drink an average of 104.5 kg (230 lb) of milk and eat approximately 12 kg (26 lb) of cheese, 7.3 kg (16 lb) of ice cream, and 2.3 kg (5 lb) of butter per capita annually. Providing consumers with milk, cheese, ice cream, and other dairy products involves collaboration among several specialized subunits, including the dairy farm, state health department, milk hauler, processing plant, and distributor.

Dairy farms are partially vertically integrated in that the dairy producer controls the genetic selection of breeding stock, breeds the animals, raises the young stock, manages the producing animals, and sells the raw product. The processors and distributors are generally independent of the producer, although some large processors are producer-owned cooperatives. Animal health is closely associated with milk production and the profits subsequently generated. Therefore, it is important that dairy farmers in conjunction with herd veterinarians practice sound management and health programs to maintain optimal herd health. As with the other food-animal species, prevention is the key to the control of diseases in dairy cattle; however, maintaining a healthy herd is also highly dependent on therapeutic drug use to treat such diseases as laminitis, anaplasmosis, pinkeye, coccidiosis, foot rot, metritis, respiratory infections, dystocia, enteritis, and, of course, mastitis.

According to a 1991–1992 survey (FSIS 1993b), 90 percent of dairy calves are removed from their dams within 24 hours, and essentially all heifer calves are given colostrum from the first milking to provide maternal antibodies and thus passive immunity. Most calves are housed individually in hutches or in pens in a barn and are fed milk until 6 to 8 weeks of age. After weaning, calves are usually raised in groups, dehorned, have extra teats removed, and are identified, usually with ear tags. Severe diarrhea (scours, 53 percent) and respiratory infections (21 percent) are the major causes of death before weaning, and between weaning and calving (11 percent and 31 percent, respectively). These two health problems together caused the death of 1.2 percent of all heifers—more than half of the total mortality losses (FSIS 1993b; APHIS 1993).

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–8 Intramammary Antibiotics Approved for Dairy Cattle

Compound

Rxa

OTCb

Lactating Cows

Dry Cows

Amoxicillin

yes

no

yes

no

Cephapirin

no

yes

yes

yes

Cloxacillin

yes

no

yes

yes

Erythromycin

no

yes

yes

yes

Hetacillin

yes

no

yes

no

Novobiocinc

yes

yes

yes

yes

Oxytetracycline

no

yes

yes

yes

Pirlimycin

yes

no

yes

yes

Penicillin

no

yes

yes

yes

Penicillin/Novobiocin

no

yes

yes

yes

Penicillin/Streptomycind

yes

yes

yes

yes

aRx = Available by prescription.

bOTC = Available over the counter.

cOTC for dry cows and Rx for lactating cows.

dOTC for low doses and Rx for high doses.

Source: Adapted from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

Disease Control and Prophylactic Treatments

Most dairy producers vaccinate heifers for diseases such as leptospirosis (81 percent), infectious bovine rhinotracheitis (IBR, 90 percent), bovine viral diarrhea (BVD, 87 percent), parainfluenza type 3 (PI3, 85 percent), bovine respiratory syncytial virus (BRSV, 66 percent), and brucellosis (65 percent). In addition, 54 percent are given coccidiostats in their feed and 60 percent are wormed. Dairy farmers also vaccinate more than 30 percent of nonlactating cows for leptospirosis, IBR, BVD, and PI3; and 22 percent for BRSV. Parasiticides are used extensively, mostly in heifers for control of coccidia and nematodes.

Therapeutic Treatment of Disease

Although vaccinations are a major means of controlling viral and bacterial infections in dairy herds, diarrhea and respiratory disease are the most common illnesses among calves and heifers. Therapeutic use of drugs is called for in the treatment of such reproductive problems as retained placentas and metritis. Among the diseases afflicting dairy cattle, mastitis is recognized as the most costly. In fact, intramammary infection (Table 2–8) is the most costly disease to U.S. animal agriculture. In Table 2–9, health costs for dairy animals are divided by functional category (Shook 1989). The mammary-gland category is the largest, accounting for approximately half of the total health costs for the dairy cow.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–9 Distribution of Health Costs ($) per Cow by Functional Categorya

Category

Laborb

Expenseb

Totalb,c

Expense (Least-Squares Solution)d

Mammary

48.3

23.76

30.20

17.80

Reproductive

17.3

8.93

11.24

11.75

Locomotive

32.2

1.08

5.37

3.74

Digestive

3.7

1.13

1.62

0.40

Respiratory

1.8

1.16

1.40

0.51

Other

13.6

5.83

7.64

3.38

Total

116.9

41.89

57.47

37.58

aCompiled by Shook (1989).

bFrom Hansen et al. (1979).

cTotal includes expense plus labor at $8.00/hour.

d From Shanker et al. (1982).

More than 80 percent of dairy farmers used veterinarians to treat sick animals and supply drugs relating back to a high level of accountability for drug use in the dairy industry. However, a substantial number of farmers also obtained drugs elsewhere. In most rural agricultural regions of the nation, many FDA-approved drugs are available over the counter at feed supply, milk plant cooperative, or general farm supply stores. In the dairy industry, as well as in all other food-animal industries, the availability and use of antibiotics make it more difficult to produce accurate statistical documentation of drug use and disease incidence.

Questions have been raised about the appropriateness of over-the-counter drug availability. However, with the dairy industry as an example, most dairy farmers are very good at recognizing commonly-encountered illnesses in their cows and calves, and they opt for the convenience of treating the animals as the need arises. This is rather successful for the dairy industry because of the active residue surveillance program and the penalties associated with drug use violations (discussed in detail in subsequent chapters). As a result, difficulties in tracking and predicting the emergence of drug resistance are increased.

Mastitis was found to be second only to milk yield in explaining variance in profit (Andrus and McGilliard 1975). Annual losses due to mastitis shown in Table 2–10 average $184 per cow (DeGraves and Fetrow 1993). Thus, with a current cow population of approximately 9.6 million, the annual cost of this disease to the dairy industry approaches $2 billion. This figure is approximately 11 percent of the total value of farm milk sales.

Organisms present in milk from mastitic cows pose little threat to human health. The bacteria that commonly cause bovine mastitis seldom cause disease in humans. Some strains of Staphylococcus aureus, a common cause of mastitis,

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–10 Estimated Annual Losses Caused by Mastitisa

Source of Loss

Loss per Cow ($)

Percentage of Total Loss

Reduced production

121.00

66.0

Discarded milk

10.45

5.7

Early cow replacement cost

41.73

22.6

Reduced cow sale value

1.14

0.1

Treatment

7.36

4.1

Veterinary services

2.72

1.5

Total loss

184.40

100.0

aAssumptions: One-third of cows infected in an average of 1.5 quarters; milk loss 856 lb per infected quarter; milk price $12.07/100 lb of milk.

Source: Dairy Field Day, Coastal Plain Experiment Station, Tifton, Georgia, June 1994.

can produce enterotoxins that cause nausea, vomiting, abdominal cramps, and diarrhea when ingested. However, if milk is cooled properly, pasteurized, and handled correctly thereafter, the danger of toxin formation is remote.

An important public health concern is the potential for antibiotics used in mastitis treatment to remain as residues in milk or meat. Careful use of antibiotics (avoidance of products not approved for use in dairy cattle, use of proper dosages, and compliance with withdrawal times specified on product labels) is intended to minimize the potential for antibiotic residues to carry over into meat and milk. Given the potential for drug residues in dairy products, the industry is seeking alternatives to antibiotic use in herd health programs.

Antibiotic Drug Use

A comprehensive program of mastitis control has been adopted for reducing the incidence of intramammary infections in dairy cows. The key is prevention of the disease, and prevention is best accomplished by improving milking hygiene and decreasing exposure to pathogens between milkings. However, new infections still occur and must be eliminated to reduce the overall incidence of mastitis in the dairy herd.

Established infections caused by major udder pathogens can be eliminated by spontaneous recovery, culling of chronically infected cows, treatment during lactation, and treatment at time of drying off (Philpot and Nickerson 1992). Spontaneous recovery occurs when the infected cow is cured of an intramammary infection without medical intervention; however, that phenomenon takes place at most in 20 percent of established infections. The majority of spontaneous recoveries occur in mammary gland quarters with mild or recent cases of mastitis and only rarely in quarters with well-established or chronic infections. Culling is

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

often used as a last resort to eliminate chronic infections from herds that are unresponsive to therapy. Consideration should be given to culling those cows whose continued presence in the herd constitutes a reservoir of infection that might ultimately spread to uninfected cows.

Obviously, spontaneous recovery and culling have serious limitations in terms of usefulness for eliminating established infections. Drug therapy remains the principal alternative for eliminating existing infections in a herd. During lactation, treatment is efficacious against some mastitis-causing bacteria and poor against others. Most preparations have been designed with little or no attention to the natural defense mechanisms operating within the udder. In addition, several host factors might influence or be influenced by antibiotic therapy. Thus, because of treatment failures, new strategies are needed to improve cure rates for existing mastitis and to reduce the incidence of new infections.

Production Enhancers

The potential to exploit hormone-dependent mechanisms to increase the production of milk has been understood for several decades. Some 50 years ago, research showed increased growth rates in rats injected with a crude pituitary extract. Later it was discovered that the extract, which contains a protein hormone called somatotropin, also affects lactation, and research with lactating cows ensued. Before the 1980s, progress was slow in bovine somatotropin (bST) research because the availability of bST was restricted to that which could be extracted from pituitary glands of slaughtered animals, limiting studies to a few cows and short time frames (OTA 1991).

In the late 1970s, new research showed that the physiological basis for more efficient milk production in genetically superior cows was the better use of absorbed nutrients. Scientists recognized the need for new concepts regarding nutrient regulation in animals. More recent work demonstrated that somatotropin exerts key control over nutrient use. When administered exogenously, either pituitry-derived or the recombinant DNA-derived analog markedly improves milk production efficiency in lactating cows. In the last decade, the refinement in production technology and development of easily used delivery technologies (i.e., long acting hormone delivery implants) has established an important role for somatotropin in the dairy industry. Today recombinant DNA-derived somatotropin is approved by FDA for use in dairy cattle to boost milk production.

THE BEEF INDUSTRY

Although cattle were brought to America in the 1620s, the practice of animal husbandry was not widespread (Thompson 1942) by current standards. By the time interest in improved cattle evolved in America, stockmen could import breeds that emerged in Europe after Robert Bakewell (1725–1795) demonstrated

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

the improvement in cattle through controlled breeding (Thompson 1942). From that period until after World War II, pure breeds were the focus of beef breeding. Crossbreeding, originally developed for adapting types of cattle for the Gulf Coast region, currently provides heterosis and genetic variation, which are needed for optimal performance in various environments. New European breeds were introduced in the 1960s, and consumer demand for less fat caused breeders to change from small-framed, early-maturing cattle to larger cattle having less fat deposition at market weight. Consumption of beef declined slightly from 48 kg (106 lb.) per capita in 1984 to 42 kg (93 lb.) in 1994. More than 10.5 billion kg (23 billion lb) of beef was produced in the United States in 1994.

The number of cattle fluctuated from 63 million to 100 million between 1925 and 1994 (FSIS 1994c). Breeding-cow herds vary greatly in size. About half have 10 to 99 cows, but 12 percent have more than 500 and 10 percent have fewer than 10 cows (FSIS 1993a). Nearly 75 percent of beef calves are born between February and May. More than 80 percent of the farms have mixed-bred cows; only 4 percent have purebreds exclusively.

At 2 to 4 months of age, calves typically are sorted by sex (bulls destined to be steers are castrated and dehorned) and tagged for identification. In 1992, on average, calves were weaned at about 7 months, when they weighed about 227 kg (500 lb) (FSIS 1993a). Ideally, for about 45 days after weaning (a period called backgrounding), calves should be fed a high-protein, high-energy concentrate and given access to high-quality hay and pasture to optimize their transition to the next phase. Following this period, calves might be fed on pasture or range similar to that for the breeding herd. More typically, they are shipped (often hundreds of miles) to stock farms, where they are fed for growth (not finishing) for up to 1 year on small grain pastures or corn or sorghum stubble (Boykin et al. 1980).

Feeding cattle in western and midwestern feedlots became much more common with the availability of inexpensive grains during the 1960s. Forty years ago, nearly all cattle were fed on small farms, mostly in the north-central region of the country. Today, feedlots are concentrated in the western corn belt, the eastern Great Plains, and the High Plains of Texas. Most feedlot cattle are purchased at auction or through order buyers (VanArsdall and Nelson 1983).

Until the 1960s, most cattle were moved large distances to slaughter plants near major population centers (Koch and Algeo 1983). More recently, meat packers have moved closer to where cattle are fed, providing advantages in labor, waste management, transportation, and efficiency. Most cattle are purchased by meat packers directly from feedlots. Packers distribute more than 95 percent of the beef in boxes directly to retail stores and fast-food chains (Knutson 1993).

Vertical integration, which typifies the broiler industry and is increasing in the hog industry, has not made much progress in the beef industry. Given the relatively disjointed structure of the beef industry, animals can be traced from the slaughter plants to the feeder and sometimes to the stock farm, but only rarely to the farm of origin.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

Disease Prevention

To safeguard against disease emergence during periods of stress, calves are given vaccinations against respiratory (for Clostridium and respiratory-disease complex) and gastrointestinal (primarily viral) diseases, and they are treated for worms and ectoparasites. After shipping, on entry into the feedlot, cattle are typically vaccinated again for Clostridium and respiratory-disease complex, further treated for worms and ectoparasites, and given a steroid-type implant for growth promotion. For 28 to 65 days they also are given a prophylactic combination of tetracycline and sulfamethazine to prevent disease during the initial stressful period accompanying feedlot entry. Other antibiotic drugs are fed throughout the finishing period, including ionophores to improve feed efficiency and growth rate and tylosin to prevent liver abscesses (Koch and Algeo 1983).

The following measures can be taken to prevent diseases in beef cattle:

  • use of adequate and balanced nutrition, which is essential for optimal immune functioning in animals;

  • elimination or reduction of the population of vectors, for example, the face fly, which transfers pinkeye; the mosquito, which transmits anaplasmosis; and the culicoid, which transmits bluetongue;

  • good pasture management, such as weed control, rotational grazing, adequate fertilizing, fresh water, and fenced-out muddy areas to help control disease infestations and prevent stress, which might leave animals, especially newborns, weak and more susceptible to disease; and

  • keeping the facilities and environment as clean as possible. Any invasive procedure, such as that requiring an esophageal tube or a syringe, should be done with clean hands and clean equipment to avoid human transmission of disease.

Trends in Drug Use

Anabolic compounds are widely used to promote weight gain and feed efficiency in cattle. Most are derivatives of reproductive steroid hormones (estrogen, progesterone, or testosterone) and generally work by interacting with specific steroid hormone receptors (Hancock et al. 1991). Residue data indicate a wide safety margin for human health in the use of those drugs in cattle (Henricks et al. 1983). Some data indicate that increases in estrogen residues from implanting steers are no greater than are those found in heifers at some stages of the natural estrus cycle (Henricks et al. 1983).

Some of the most devastating cattle diseases, such as foot-and-mouth disease, brucellosis, and tuberculosis, have been controlled through national eradication and surveillance programs. Others, such as clostridial infections, are controlled by vaccination. Respiratory diseases are managed by mass vaccinations and treatment of affected individuals. Such diseases as diarrhea are managed by treatment of individual calves.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

Because the largest potential for creating drug residues in beef tissues arises from treatment of cattle in feedlots, feedlot operators emphasize control of infectious diseases at the time cattle enter the lot, 2 to 4 months before slaughter (the duration of this period depending mostly on the price of grain and on market prices for finished cattle). Various feed additives (Tables 2–11 and 2–12) and implant treatments are approved for use throughout the feeding period. Eight feed-additive antibiotics are labeled for improved growth or feed efficiency. Shepard et al. (1992) also list 11 antibiotics with no claims for growth or feed efficiency, 18 parasiticides and 6 sulfonamides for cattle, and 3 estrus synchronizers for beef cattle and dairy heifers. The parasiticides include 11 wormers, 2 coccidiostats, 4 ectoparasiticides, and 1 endectocide. Additionally, insecticides and insecticidal ear tags for beef cattle are approved by EPA.

Therapeutic Drug Use

Therapeutic use of drugs in cattle is often necessary. Most commonly drugs are administered for enteric and respiratory diseases in calves and feeder cattle, and for reproductive infections in breeding herds. Although therapy is more expensive than preventing disease and injury through the use of healthful conditions and vaccination, it is necessary when these measures fail. The costs incurred are for:

  • medication;

  • visits by the veterinarian;

  • additional time required to move infected animals to and from the treatment area;

  • segregation of infected animals, which might involve separate feeding, watering, shelter, and observation;

  • weight loss;

  • reduced value of chronic cases that never return to their original condition; and

  • death.

Feeding low concentrations of antibiotics to cattle with the intention of increasing the dose as signs of disease occur is different from subtherapeutic feeding to increase weight gain. The method of administration is through feed rather than injection, but the intention is therapeutic. Cattle are sometimes fed low concentrations of antibiotics during particularly stressful times when they are most apt to get sick—for example, at weaning or after being shipped a long distance. That regimen might be used for 2 or 3 weeks. Data from the former National Cattleman’s Association (1995) suggest that penicillins are not used for growth promotion in cattle and that the use of tetracyclines is in sharp decline as

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–11 Major Claims for Systemic Antimicrobials Approved for Use in Beef and Dairy Cattle

Compounds

Respiratory Infections

Diarrhea

Mastitis

Other Infections

Growth and Feed Efficiency

Antibiotics

 

Amoxicillina,b

yes

yes

no

yes

no

Ampicillina,b

yes

no

no

yes

yes

Bacitracin

no

no

no

yes

yes

Ceftiofura,b

yes

no

no

no

no

Chlortetracyclineb

no

no

no

yes

yes

Dihydrosteptomycinb

no

no

no

yes

yes

Erythromycinb

yes

no

no

yes

no

Furamazone

no

yes

no

no

no

Gentimycin

no

no

no

yes

no

Lasalocida

no

no

no

no

yes

Monensinc

no

no

no

no

yes

Neomycinb

no

no

no

yes

no

Oxytetracycline (oral)b

no

no

no

no

yes

Oxytetracycline (injection)b

yes

yes

no

yes

no

Penicillinb

yes

no

no

yes

no

Streptomycin

yes

yes

no

yes

no

Tetracycline

yes

yes

no

no

no

Tilmicosina

yes

no

no

no

no

Tylosind

no

no

no

yes

no

Sulfonamides

 

Sulfabromomethazine

yes

yes

yes

yes

no

Sulfachloropyridazine

no

yes

no

no

no

Sulfadimethoxineb

yes

no

no

no

no

Sulfaethoxypyridazinea

yes

yes

yes

yes

no

Sulfamethazine

yes

yes

yes

yes

no

Sulfamethoxine

yes

no

no

no

no

aAvailable by prescription only.

bApproved for lactating cattle.

cFor beef and pastured cattle.

dPreventive liver abscesses claim only.

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–12 Steroid Products Labeled for Improved Growth and/or Feed Efficiency in Cattle

Compound

Steers

Heifers

Estradiol

yes

yes

Estradiol/Progesterone

yes

no

Estradiol/Testosterone

no

yes

Estradiol/Trenbolone

yes

no

Melengestrol

no

yes

Trenbolone

yes

yes

Zeranol

yes

yes

 

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

a result of the suggestion to limit the use of these drugs pending results of research on human health.

Vaccinations

Like dairy cattle, beef cattle are vaccinated against brucellosis, leptospirosis, clostridial infections, and a bovine respiratory complex of diseases, which usually include IBR and PI3. Many outbreaks of disease in herds can be prevented on farms with good vaccination programs.

THE VEAL INDUSTRY

After World War II the number of calves, mostly cull males from dairy breeds, marketed for veal rose to more than 13 million (Knutson 1993), which at that time was similar to the number of dairy cattle. Most of these calves were “bob” veal, which were only a few days old and weighing about 100 pounds. The number of veal calves fell continuously from 1945 to about 1.4 million in 1992.

The veal calf industry as it exists today originated in the late 1960s. For veal, up to 0.9 million cull dairy bull calves are purchased at less than 1 week of age, mostly at auction (Wilson 1993). Typically, a veal farmer can receive more than 100 calves, originating from about 50 farms, to start a cycle. Throughout its 16-to 18-week feeding period, the veal calf is housed individually in a stall and maintained as a preruminant by feeding commercially available milkbased liquid diets. The starter usually contains an antibiotic (e.g., oxytetracycline). Typically, beginning at 4 to 6 weeks of age, the starter is gradually replaced with a liquid grower diet with less protein and limited iron and containing no antibiotic. The calves are slaughtered at 400 to 500 lb body weight. Iron is limited to create pale

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

muscle, but without anemia, because red blood cells have a higher priority for limited iron. The price paid for the calf is reduced proportionately to the intensity of red color in the muscle.

Veal calves encounter the same diseases as do other calves, particularly enteric and respiratory infections. FDA recently created a new policy for drug usage. Out of concern for veal animal well-being and for the industry, FDA now permits the use of some drugs already approved for beef or dairy cattle when they are used in veal calves under a valid veterinarian–client–patient relationship (VCPR) to ensure safe drug use and optimize animal health. Wilson (1993) listed 8 antibiotics, 2 sulfonamides, and 2 anthelmintics, which were used extralabel in veal calves under valid VCPRs.

Since 1991, 3 drugs have been labeled for veal calves: amoxicillin (respiratory infections), ampicillin (enteric infections), and decoquinate (coccidiosis). To assist in labeling new drugs for use in veal calves, USDA recently classified veal as a minor-use species, making research on calves eligible for funds in the IR4 program for new-drug approval.

THE SHEEP INDUSTRY

The number of sheep worldwide has risen almost continuously. In the United States, however, after a peak of about 56 million in 1942 (Parker and Pope 1983), the stock declined to about 10 million in 1985 (the lowest since records were begun in 1867), and remained relatively constant thereafter. Sheep now account for less than 1 percent of the U.S. red-meat consumption (Knutson 1993). Most marketed sheep derive from one or more of eight major breeds. Numbers of sheep in the smaller breeds have declined, while the larger breeds increased, reflecting demand for larger carcasses. Texas (20 percent), California (9 percent), Wyoming (9 percent), Colorado (7 percent), South Dakota (6 percent) and Montana (5 percent) account for 56 percent of the U.S. sheep flock (Knutson 1993).

Typically, in the western states, federal ranges have provided half of the feed for commercial sheep (Parker and Pope 1983). In that region, most ewes lamb in the spring on open range under the care of herders. Others are housed and fed feeds stored for the winter, and are lambed in sheds to optimize lamb survival. Grazing begins in the spring at the lower elevations and follows the receding snow toward higher elevations as spring and summer progress. Some slaughter lambs come directly from these ranges, more when forage is better, but most range lambs are sold or contracted to feedlots for finishing. Some feedlots have a capacity for more than 30,000 lambs.

Sheep are managed much more intensively in most of the rest of the country (Parker and Pope 1983). For example, in the north-central states, lambs often are weaned at 4 to 6 weeks of age and moved directly to dry lot feeding. This reduces the need for high-quality forage, minimizes worm infections and predation, and

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–13 Major Claims of Antibacterials Approved for Use in Sheep

Compound

Growth and Feed Efficiency

Various Infections

Chlortetracycline

yes

yes

Erythromycin

no

yes

Neomycin

no

yes

Oxytetracycline

no

yes

Penicillin

no

yes

Penicillin/Streptomycin

no

yes

 

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

increases the number of lambs marketed at seasonally high prices. Although this system requires more grain feeding, grains are readily available and can be the most economical source of energy in the region. The system also permits the farmer to maintain about 50 percent more ewes and to optimize the proportion of ewes that breed to lamb at 12 to 14 months of age. The most intensive management achieves 3-lamb crops with up to 6 lambs every 2 years; more than double the current national average. This system includes estrus synchronization, the use of gonadotropins to optimize twinning, hand mating or artificial insemination, pregnancy diagnosis, induced parturition, and artificial rearing of lambs, especially when ewes are not good mothers (Newton 1982; North 1984). However, most of the appropriate hormones required for this kind of management are not approved for use in sheep.

Kimberling (1988) outlined the diseases of sheep, most caused by bacteria, viruses, and parasites. Vaccines are available to prevent several infections, such as vibriosis, enzootic abortion, epididymitis, enterotoxemia (Clostridium perfringens), and bluetongue. Although antibacterials are helpful for treating lambs with enteritis, enterotoxemia, or colibacillosis, they are critical to control respiratory diseases, including shipping fever. Six antibiotics are approved for use in sheep (Shepard et al. 1992, [Table 2–13]). There are no sulfonamides labeled for sheep, although they apparently have been used (Parker and Pope 1983).

Parasites, both internal and external, can be devastating to sheep. In two model programs in the United States, the screwworm has been controlled by release of sterile flies, and mange mites have been eradicated by mandatory dipping of sheep before interstate movements (Parker and Pope 1983; Kimberling 1988). Four compounds are labeled to control worms in sheep, and at least one anthelmintic treatment is critical for pastured lambs. Lambs entering a feedlot typically are given an anthelmintic, a broad spectrum antibiotic, and an implant

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

of zeranol. One antibacterial has claims for improved feed efficiency and growth rate, in sharp contrast to the numbers approved for cattle (Table 2–8), hogs (Tables 2–6 and 2–7), and broiler chickens (Table 2–2). Sheep are known to respond like cattle, with improved growth and feed efficiency, when given various steroids, but only zeranol is approved for sheep. Similarly, like cattle, sheep respond with improved feed efficiency when given ionophores, but none is approved with this claim for sheep. Lasalocid, an ionophore, which is approved for enhanced growth and feed efficiency in cattle, has a claim only for the control of coccidiosis in “confined” sheep.

Sheep numbers could increase as management strategies for this industry shift from an extensive, range-based program to intensive management systems, with an attendant increase in the need for some kinds of drugs and chemicals. The examples are feed-additive antibiotics, products for growth promotion, and steroid implants approved for cattle. At this time, however, the sheep industry is too small to justify the investments required to develop many drug products, particularly those that would be used only for sheep.

MINOR SPECIES

Goats are the most important of the minor food animals. The minor species suffer from most of the same kinds of diseases that are found among major species. Goats, for example, have the same variety of enteric, respiratory, nematode, and ectoparasite infections as do sheep and cattle. However, only 6 drug products are labeled for goats (Shepard et al. 1992): 2 for coccidiosis, 2 wormers, and 2 antibiotics (Table 2–14). Potential profit from such products usually is too small to recover the costs of developing them, often even when the active ingredient is already marketed for major species. This shortage of drugs to manage disease is even more vexing for the other minor species. In fact, there are no drugs labeled for use in species such as bison, geese, and squab.

Undoubtedly, the lack of drugs, the discouraging marketing opportunities, and the limited research and information assistance from the government all contribute to contain growth of the minor-species industries. For producers, the only access to many drugs is through extra-label use of products developed for other species with the aid of a valid VCPR. FDA allows this kind of use for some drugs to promote animal well-being and because the industries probably could not exist even in their current form without some of the key drugs.

THE AQUACULTURE INDUSTRY

Aquaculture in the United States is growing rapidly. This industry is now considered an important supplier of food products for U.S. consumers. Inventories of food-size catfish in 1995 were estimated at 202 million fish, up 7 percent in 1994; tilapia production increased to 6.8 million kg (15 million lb) in 1994 and

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–14 Major Claims for Drugs Approved for Use in Minor Species

Species

Compound

Claims

Reindeer

Ivermectin

Grubs

Duck

Chlortetracycline

Growth, feed efficiency, various infections

 

Novobiocin

Various infections

Goat

Decoquinate

Coccidiosis

 

Monensin

Coccidiosis

 

Neomycin

Enteritis

 

Penicillin/ streptomycin

Various infections

 

Phenothiazine

Worms

 

Thiabendazole

Worms

Pheasant

Amprolium

Coccidiosis

 

Bacitracin

Growth, feed efficiency, various infections

 

Penicillin

Growth, feed efficiency

 

Thiabendazole

Worms

Quail

Bacitracin

Growth, feed efficiency, various infections

 

Monensin

Coccidiosis

 

Penicillin

Growth, feed efficiency

Rabbits

Penicillin/ streptomycin

Various infections

 

Sulfaquinoxaline

Coccidiosis

 

Source: Compiled from FDA Approved Animal Drug List (Green Book), 1998a, and Feed Additive Compendium, 1997.

continues to rise; and salmon production was approximately 11.8 million kg (26 million lb) in 1993 and remained the same in 1994. In 1995, farmer sales of catfish to processing plants were approximately 20.9 million kg (460 million lb), up 6 percent from 1994. U.S. oyster growers have not been able to increase production sufficiently to meet increasing demands for exports to Asia, Japan, Taiwan, and Canada. Total sales of trout rose 13 percent in 1995, an increase attributed to higher sales of food-size fish, which rose 6 percent to $60.8 million. Exports of oysters reached $6.9 million in 1994, up more than 180 percent from exports in 1991. Because of the near collapse in the stocks of cod, halibut, and several other species, the U.S. and Canadian governments have imposed severe harvesting cutbacks in the Georges Bank fishing area of the northern Atlantic. As a result, both countries have placed increased priority on cultivation of these species.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

As with other food-animal industries, aquaculture is becoming a more concentrated industry of fewer but much larger farms. The vast majority of fish-farming enterprises in the United States where medications might be used are pond-like or tank structures, rather than open-water habitats, such as oceans and lakes. In contrast, some countries like Norway utilize natural structures, such as the fjords for salmon farming, and there are concerns about the wastes collecting in fjord bottoms. In the United States, approximately 158,800 acres of ponds were devoted to catfish production in 1995, but the number of farms decreased. Tilapia production in the United States has focused on the live-fish market, because import requirements and high costs restrict live-fish import. This market continues to expand, however, and production of tilapia in tank systems for processed products is likely to grow.

Aquaculture encompasses production of various sizes and types of fish. Brood fish are kept to produce the fertilized eggs that go to hatcheries. Food-size fish include (1) small fish, weighing 0.34 to 0.7 kg (0.75 to 1.5 lb); (2) medium fish, weighing 0.7 to 1.4 kg (1.5 to 3 lb); and (3) large fish, weighing more than 1.4 kg (3 lb). Large stocker fish weigh from 82 to 341 kg (180 to 750 lb) per 1,000 fish, and small stocker fish weigh from 27 kg to 82 kg (60 to 180 lb) per 1,000 fish. Fingerlings or fry fish weigh 27 kg (60 lb) per 1,000 fish.

The use of antibiotics and drugs in the fish industry is complicated because of the need to administer the compounds, for the most part, directly into the water in which the fish swim. The safety of aquatic food products, the integrity of the environment, the safety of target animals, and the safety of persons who administer various compounds are important issues that have an effect on drug use in the aquaculture industry. As with other food-animal industries, industry-developed and industry-directed aquaculture quality-assurance programs are preferred to monitor compounds that come into contact with food fish.

Compounds commonly used in the aquaculture industry that might be considered a potential threat to food safety and consumer health include animal drugs and veterinary biologics, pesticides, disinfectants, and water-treatment compounds. New animal drugs that are added to aquaculture feed are subject to FDA approval and must be specifically approved for use in aquaculture feed. These drugs must be mixed in feed at concentrations that are specified in FDA medicated-feed regulations.

Water treatments used in aquaculture include chemicals that are applied directly to water for control of algae or water-borne parasites. The selection of the federal agency that will have jurisdiction over a particular chemical depends on the intended use of the product in the water. Chemical residues in fish can occur from improper use or application of water treatments to improve fish health or improper use of products to control weeds or water quality.

New animal drugs approved by FDA for use in the aquaculture industry appear in Table 2–15. There are several unapproved compounds of low regula-

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

TABLE 2–15 FDA-Approved New Drugs for Use in Aquaculture

Drug

Active Ingredient

Indication

Species

Finquel, MS-222

Tricaine methanesulfonate

Sedation/anesthesia

Fish (Ictaluridae, Salmonidae, Esocidae, Percidae), other aquatic poikilotherms

Formalin-F; Paracid-F; Parasite-S

Formalin

Control protozoa and monogenetic trematodes (Icthyopthirius, Chilodonella, Costia, Scyphidia, Epistylis, Trichodina spp. and Cleidodiscus, Gyrodactylus, Dactylogyrus spp.)

Salmonids, catfish, largemouth bass, bluegill

 

 

Control fungi of the family Saprolegniaceae

Salmodi and esocid eggs

Parasite-S

Formalin

Control protozoan parasites (Bodo spp., Epistylis spp., and Zoothamnium spp.)

Panaeid shrimp

Romet-30

Sulfadimethoxine and ormetoprim

Control furunculosis (Aeromonas salmonicida)

Salmonids

 

 

Control enteric septicemia (Edwardsiella ictaluri)

Catfish

Terramycin

Oxytetracycline monoalkyl trimethyl ammonium

Mark skeletal tissue

Control ulcer disease, furunculosis, bacterial hemorrhagic septicemia, and pseudomonas disease (Hemophilus piscium, Aeromonas salmonicida, Aeromonoas liquefaciens, Pseudomonas)

Pacific salmon

Salmonids

 

 

Control bacterial hemorrhagic septicemia and pseudomonas disease

Catfish

 

 

Control gaffkemia (Aerococcus viridans)

Lobster

 

Source: Adapted from Drugs Approved for Use in Aquaculture, Center for Veterinary Medicine, U.S. Food and Drug Administration, Revised June, 1995; http://www.fda.gov:80/cvm/fda/infores/other/aqua/appendixa.html

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

tory priority to FDA. FDA’s enforcement position on the use of these substances is not one of approval or affirmation of their safety.

QUALITY-ASSURANCE PROGRAMS AND ANIMAL HEALTH MAINTENANCE

Animal health products must be handled and administered properly if producers are to maintain public trust and be competitive in U.S. and world markets. Important objectives to producers are reducing the risk of drug residues in food products, and, ultimately, eliminating irresponsible drug use, so that public perceptions of poor drug management are changed with the result that consumer confidence increases.

Food-animal producers know that the profitability of the production facility is directly linked to not only the quality and efficiency of animal management but also to the perceptions of the public regarding the industry and the overall appeal of the product. Stresses on animals must be managed and minimized, so that the animal can achieve its genetic potential for growth and productive metabolism rather than expend energy fighting disease. Quality-assurance programs in the food-animal industry focus on helping producers supply products that are as free as possible of microbiological hazards, and drug and chemical residues. The consumer is presented with products obtained from animals that received proper care.

All major livestock-producer groups have initiated quality-assurance programs to address their responsibilities in producing safe, wholesome products. Among such groups are the National Pork Producers Council (NPPC), the National Cattlemen’s Beef Association, the National Milk Producers Federation, the American Sheep Industry Association, the American Veal Association, the National Broiler Council, the National Turkey Federation, the United Egg Producers, the Catfish Farmers of America, the National Aquaculture Association, and the U.S. Trout Farmers Association.

The following sections describe the quality-assurance programs initiated by the National Broiler Council, the National Turkey Federation, NPPC, the National Cattlemen’s Beef Association, and the National Milk Producers Federation.

Poultry Quality-Assurance Programs

In the United States, with the help of various public and private institutions and the implementation of the National Poultry Improvement Plan (NPIP) of 1935 and the National Turkey Improvement Plan of 1943, the poultry industry has been able either to eradicate or to minimize disease exposure. That undertaking has improved profitability and expanded the industry.

The eradication of various diseases caused by Mycoplasma gallisepticum, Mycoplasma synoviae, Mycoplasma meleagridis, Salmonella pullorum, and Sal-

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

monella gallinarum; velogenic Newcastle disease; and highly pathogenic avian influenza could not have been accomplished without the NPIP system.

The goal of the National Turkey Federation’s Chemical Residue Avoidance Program is to ensure that the tissue of turkeys produced and slaughtered in the United States will not contain any chemical residues and will meet or exceed all tolerance and action levels for known harmful residues as established by the federal regulatory agencies (the U.S. Environmental Protection Agency, FDA, and the USDA Food Safety and Inspection Service [FSIS]).

The National Broiler Council’s recommended Good Manufacturing Practices address every quality-control point in the production and processing of broiler chickens to enhance product quality and consumer protection. The procedures are drawn from quality-control programs throughout the broiler industry, from the scientific literature, and from existing regulatory documents. In production, recommended practices include:

  • maintaining proper facility standards,

  • providing growers with pesticide information,

  • including pesticide-use statements in grower contracts, and

  • enforcing biosecurity programs.

Regarding animal health care, the following practices are recommended:

  • ensuring that pharmaceutical laws and regulations are followed (only FDA-approved pharmaceuticals and regimens are to be used), and

  • enforcing company standards for pharmaceutical use.

In breeder operations, standards are to be maintained for feeds and animal health. In addition, procedures to control poultry-borne and egg-borne pathogens and diseases should be a routine part of breeder-monitoring programs. Hatchery recommendations address sanitation and microbiological controls, which continue through the growing period, transport, slaughter, and processing. Testing for microbiological quality, pesticide and chemical residues in feed ingredients is recommended for feed preparation during the growing period. Maintaining records of feed distribution and pharmaceutical inventories, and ensuring that FDA regulations are adhered to, are important aspects of good poultry management practice.

Pork Quality-Assurance Programs

In June 1989, NPPC introduced a management education program called the Pork Quality Assurance (PQA) program. It was designed to help producers avoid violative drug residues, improve management practices, reduce production costs, and increase awareness of food safety concerns. The PQA program emphasizes

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

good management practices in the handling and use of animal health products and encourages producers to review their herds’ health programs annually.

The program provides information covering the following topics:

  • food safety and the pork industry,

  • products used today,

  • routes of administration,

  • on-farm feed preparation,

  • minimum withdrawal times,

  • current regulatory system, and

  • on-farm testing.

The PQA program (NPPC 1997) was developed by NPPC to institute safety, uniformity, and consistency in the production of pork. The program refers to three achievement levels in the quality-assurance certification process. Levels I and II are self-instructional and self-paced reading from a booklet obtainable from NPPC. All producers are encouraged to learn and implement the 10 “good production practices” defined in the booklet. Producers can achieve Level III through a professional consultation, which takes them step-by-step through the design of a herd health program. For producers this 10-step program is developed around the appropriate uses of medications and the need for accountability. The plan results in an understanding of the need for the oversight of the veterinarian and in written accounts of animal-by-animal drug use. Level III of the PQA program applies principles from the Hazard Analysis and Critical Control Points (HACCP) to the production of pork. The HACCP involves determining where problems could develop and establishing procedures to monitor those problems. To complete Level III, a producer must annually perform the following 10 critical control points:

  1. Establish an efficient and effective herd health-management plan.

  2. Establish a valid veterinarian, client, and patient relationship.

  3. Store all drugs correctly.

  4. Use only FDA-approved over-the-counter or prescription drugs with professional assistance.

  5. Administer all injectable drugs and oral medications properly.

  6. Follow label instructions for use of feed additives.

  7. Maintain proper treatment records and adequate identification of all treated animals.

  8. Use drug-residue tests when appropriate.

  9. Implement employee and family awareness of proper drug use.

  10. Complete quality-assurance checklist annually.

In the implementation of the PQA program, extensive cooperation has been

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

received from veterinarians, packers, media, agriculture teachers, FDA, FSIS, extension personnel, feed manufacturers, and pharmaceutical companies.

Producer response to the PQA program has been favorable. As of July 1, 1995, approximately 32,000 pork producers who provide 63 percent of the market hogs in the United States were enrolled in the program. Thirty percent of U.S. pork is from producers who have completed the program and an even larger percentage comes from producers who have implemented some aspects of the program.

According to the 1993 nationwide monitoring program administered by FSIS, violative residues for sulfamethazine and antibiotics in market hogs have decreased (FSIS 1993c). The violation rate for sulfamethazine has continued to remain low in recent years. FSIS has congratulated NPPC for its work in reducing the violation rate and has encouraged the NPPC membership to continue to follow the recommendations in the PQA program to avoid illegal residues. To continue reducing violative drug residue rates and reach the industry goal of no violative residues, NPPC urges all producers to enroll in and complete the PQA program.

In addition to its Compliance Policy Guides directed toward use of animal health products by veterinarians, FDA has issued a Compliance Policy Guide on Proper Drug Use and Residue Avoidance by NonVeterinarians. The objective of this guide is to ensure proper use of animal health products in food-producing animals when administered by producers. The guide describes the records FDA inspectors would ask to see when doing on-farm investigations after a violative drug residue has been discovered. The guide addresses identification of treated animals; maintenance of treatment records; storage, labeling, and accounting of medications; use of prescription products only through a valid VCPR; and education of employees and family members. The PQA program provides a means for producers to comply with the FDA guide.

Dairy Quality-Assurance Programs

To ensure that only the highest quality dairy foods and residue-free products reach the consumer, two important documents have been developed. The first was the Grade A Pasteurized Milk Ordinance, also known as the FDA PMO (FDA 1995b). The premise of the original PMO, developed in 1924, was that effective public-health control of milk-borne diseases required the application of sanitation measures through the production, handling, pasteurization, and distribution of milk and milk products.

The second document was the Milk and Dairy Beef Residue Prevention Protocol (Boeckman and Carlson 1995), which addresses the need to market residue-free milk and dairy beef. That 10-point plan for the Milk and Dairy Beef Quality Assurance Program was developed by the National Milk Producers Federation and the American Veterinary Medical Association (AVMA). Both organizations emphasized that the plan would require cooperation and communica-

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

tion between dairy farmers and veterinarians, so that the industry could remain active in preventing drug residues in milk and beef. In the plan’s guidelines, the producer is viewed as providing a safe product, and the consumer as benefiting by drinking uncontaminated milk. The 10-point plan has been adopted as part of the PMO by individual states, and it is mandatory for all producers after one contaminated load of milk is detected.

An extremely important aspect of quality-assurance programs is the establishment of a valid VCPR. This relationship ensures that farm animals receiving antibiotics will be withheld from the food chain until drug concentrations are below those permitted by FDA. Both the producer and the veterinarian must work closely with quality-assurance program coordinators and extension personnel to ensure that the drug-avoidance programs are followed.

The 10-point quality assurance plan deals specifically with the drug-residue issue and for milk and dairy beef production includes:

1) Practicing healthy-herd management. Investments in disease prevention are more cost-effective than is disease treatment. Some examples include proper milking management versus treatment of clinical mastitis, good hoof care and trimming versus treatment of foot infections, calving cows in a sanitary location versus treatment of uterine infection, and proper vaccination versus treatment. Producers are encouraged to practice herd health management by consulting with licensed veterinarians and other related professionals.

2) Establishing a valid VCPR. AVMA (1998) defines a VCPR as follows:

An appropriate veterinarian/client/patient relationship is characterized by these attributes: (1) [t]he veterinarian has assumed the responsibility for making medical judgments regarding the health of the animal(s) and the need for medical treatment, and the client (owner or other caretaker) has agreed to follow the instructions of the veterinarian; and when (2) [t]here is sufficient knowledge of the animal(s) by the veterinarian to initiate at least a general or preliminary diagnosis of the medical condition of the animal(s). This means that the veterinarian has recently seen and is personally acquainted with the keeping and care of the animal(s) by virtue of an examination of the animal(s) and/or by medically appropriate and timely visits to the premises where the animal(s) are kept; and when (3) [t]he veterinarian is readily available, or has arranged for emergency coverage, for follow-up in the event of adverse reactions or failure of the treatment regimen. (Pp. 49–50)

A valid VCPR is mandatory if drugs are to be used for reasons different from those stated on the label; this is called an extra-label use. Dairy farmers need the benefit of a valid VCPR to make sure they are following the veterinarian’s instructions properly.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
×

3) Using only FDA-approved over-the-counter or prescription drugs with a veterinarian’s guidance.

FDA-approved drugs have been tested extensively to show that they perform consistently according to the manufacturer’s claims and that they cause no harm to the animal when administered according to the label. As a result, dairy farmers will reduce the risk of violative drug residues in the milk and meat of animals receiving drugs and protect their market by supplying safe and wholesome milk and meat.

FDA-approved over-the-counter drugs are those that can be purchased anywhere without a veterinarian’s prescription or supervision. Drugs are labeled for over-the-counter sale when instructions that are adequate for a layperson can be printed on the label, including the package insert.

4) Ensuring that all drugs have labels that comply with state or federal labeling requirements. Because dairy farmers are ultimately responsible for any drug residues, they should be careful to follow drug label instructions. They should not be concerned about the accuracy of a label, because the manufacturer must meet all the requirements to get the drug approved, and veterinarians are responsible for all labels of drugs they prescribe for their clients’ animals.

5) Storing all drugs correctly. All medications for cattle must be properly stored, so that they will not come into contact with milk or the milking equipment. Topical antiseptics, wound dressings, vaccines, and other biological products and vitamins or mineral products are generally exempt from labeling and storage requirements. However, some states might have specific storage regulations.

6) Administering all drugs properly and identifying all treated animals. The best way for dairy farmers to avoid problems associated with this critical control point is simply to follow the drug’s label and package insert, and to identify each animal that receives the drug at the time it is administered. Immediate identification of the animal will greatly reduce the risk of putting adulterated or contaminated milk into a tank or sending an animal with tissue residues to slaughter.

7) Maintaining and using proper treatment records on all treated animals. Dairy farmers must identify treated animals with a paint stick, leg bands, hock markers, neck strap, numbered ear tags, or other marking devices. Proper identification is crucial for keeping violative drug residues out of milk and meat. Equally important is maintaining a record of all treated animals. The records should be accessible to everyone who works with the animals. The records need to be used to ensure that cull cows, dairy beef, steers, or calves whose markings have worn off are not sold before the withholding time has expired. The records also should be permanent, so the veterinarian can refer to them to prescribe effective therapy and to serve as protection in case of a regulatory follow-up.

8) Using drug-residue screening tests. New technology has made it possible to conduct milk, urine, and blood tests that are easy to use on the farm. Many of these tests are as sensitive as those done at milk or slaughter plants. On-farm testing gives dairy farmers an additional way to avoid violative drug residues in

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
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meat and milk. The key is to match the drug administered with the correct drug test at the desired level of sensitivity.

9) Implementing employee and family awareness of proper drug use to avoid marketing adulterated products. Many cases of adulterated meat or milk occur because one person treats the animals and someone else takes care of the milking or decides to sell the animals. If different individuals are carrying out those tasks, it is important that the critical control points of the quality-assurance program be explained to everyone involved with the animals.

10) Performing the 10-point Milk and Dairy Beef Residue Prevention Protocol annually. Producers need to go through these 10 points with their veterinarians at least once a year. Conditions on the farm change; new employees are hired and different drugs are used because of a change in herd health. In addition, new drugs or screening tests come onto the market. These factors make it worthwhile for producers to review the plan with their veterinarians and farm staff a minimum of once each year.

Voluntary implementation of the 10-point plan has met with varied success. Even highlighting the incentive of reduced costs associated with a herd health program and the reduced need for drugs has not been completely effective. The Implementation and Communication Subcommittee of the Drug Residue Committee (Buntain et al. 1993) reviewed the quality-assurance initiatives and suggested that insurance companies sponsor premium reductions or price breaks on liability insurance for voluntary participants. Another suggestion was for milk processors and cooperatives to include plan participation in their requirements for quality bonuses. The cooperatives and processors could then use the information as a marketing advantage and advertise that a high percentage of their producers participated in the residue-prevention program. Another possible incentive mentioned was to have voluntary implementation of the 10-point plan defer the penalty of a first violation under the PMO. Suggestion was also made for veterinarians to go through the 10-point plan at no charge to producers who implement the plan voluntarily.

Although the incentive of reduced costs associated with a sound herd health program has not enticed a majority of producers to adopt the 10-point plan voluntarily, it still should be a major focus of preventive herd health management. The resulting decrease in disease and increase in production also would lead to a decrease in finding violative drug residues. Residue avoidance would be best served by encouraging and emphasizing the need for on-farm treatment records. The use of treatment records as a source of residue information for withholding milk and meat from the market is obvious. Establishing drug use patterns from treatment records on each farm also would provide a basis for discussing changes in or alternatives to current drug use. This information could provide opportunities for educating producers about better management alternatives in certain stages of the production cycle.

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
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Continuing-education programs on current and changing regulations are necessary for inspector, veterinarian, and producer groups. A centralized task force, perhaps encompassing extension personnel, would be helpful in gathering and reviewing the educational, labeling, and form material available, and distributing the most up-to-date information to producers. Along with details on changing regulations, information needs to be made available on sources such as Food Animal Residual Avoidance Databank (FARAD) project for determining withholding times of extra-label drugs, on drugs prohibited from use in food animals, on the liability associated with drug labeling and signing the 10-point plan, and on the definition of a valid VCPR. The relationship and importance of FARAD to drug use policy in the United States is further detailed in Chapter 3.

Beef Quality-Assurance Program

In 1996, the beef industry initiated the Beef Quality Assurance (BQA) program, a voluntary initiative designed by producers for producers (NCBA 1997). Because of the tremendous diversity across the United States in the beef cattle industry, the BQA program is implemented state by state. Although the National Cattlemen’s Beef Association provides technical support and national leadership to beef cattle producers, the administration and implementation of the BQA program are carried out by state cattle affiliates and state beef councils, with the assistance of practicing veterinarians.

The BQA program is designed to educate and train beef cattle owners, their employees, and their veterinarians on the day-to-day management practices that influence the safety, wholesomeness, and quality of beef. Subjects emphasized through producer and veterinarian seminars, workshops, and chute-side demonstrations are (1) the importance of proper and safe animal drug use; (2) adherence to product label withdrawal periods; and (3) record-keeping relative to animal product use, drug inventories, and animal treatment regimens. The program teaches testing procedures for sampling and analyzing feed and feed ingredients for potential chemical and pesticide residues at the farm or feedlot. Through the BQA program, residue drug violations for feedlot cattle essentially have been reduced to zero, as reported by the USDA Residue Monitoring Program (FSIS 1994b).

In the past few years, the BQA program has launched an aggressive effort designed to eliminate injection site tissue damage resulting from intramuscular administration of animal health products. Educational efforts regarding injection site awareness have resulted in a significant reduction in tissue quality defects. The success of these efforts demonstrates the ability of the BQA program to create an effective and responsive network of cattlemen and veterinarians.

The BQA initiative is structured to reach all segments of beef cattle production, including cow and calf, stocker, backgrounding, and feedlot operations. To date, 42 states sponsor aggressive BQA programs. These states produce more

Suggested Citation:"2 Food-Animal Production Practices and Drug Use." National Research Council. 1999. The Use of Drugs in Food Animals: Benefits and Risks. Washington, DC: The National Academies Press. doi: 10.17226/5137.
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than 98 percent of the feedlot cattle and account for more than 95 percent of the cow and calf producers in the United States.

More recently, the state BQA programs have implemented producer BQA certification programs. The certification procedure requires a specified amount of structured quality-assurance training and the verification of quality-assurance practices implemented in the actual operation. It is expected that the momentum for quality-assurance certification will increase throughout the industry.

Finally, the BQA program is prepared to launch a major quality-assurance initiative for cull dairy and beef cows. Violative drug residues in cull dairy and beef cows remain a major concern for the industry.

The industry’s BQA program is an effective producer network for addressing product safety concerns now and in the future. However, on-farm food safety interventions must develop around sound science if these efforts are to be effective and further enhance the safety of beef and beef products.

SUMMARY OF FINDINGS

Across all major species of animals used in food production, the development of intensive production practices has changed the way animals are exposed to pathogens in their environment. All species, including fish, derive some benefit from the use of antibiotics to treat active infections, prevent disease outbreaks, or modify their internal environment for faster growth with the use of less feed. Because animals typically are raised in close proximity to one another, the emergence of disease in one animal can result in the rapid infection of many more in a short time, underscoring the need to use subtherapeutic concentrations of antibiotics. Animal producers must adhere to strict guidelines on antibiotic use to ensure that drug residues are not carried over into the human food chain. As such, medication is halted before slaughter to curb the inappropriate introduction of drugs and their residues into the human food chain. Opportunities exist with the use of HAACP quality-assurance programs to modify production and animal-handling strategies, to minimize the incidence and management of disease, and to control the misuse of drugs and pharmaceuticals that could allow drug residues to enter the food chain or for disease pathogens to pose a risk to human health.

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The use of drugs in food animal production has resulted in benefits throughout the food industry; however, their use has also raised public health safety concerns.

The Use of Drugs in Food Animals provides an overview of why and how drugs are used in the major food-producing animal industries--poultry, dairy, beef, swine, and aquaculture. The volume discusses the prevalence of human pathogens in foods of animal origin. It also addresses the transfer of resistance in animal microbes to human pathogens and the resulting risk of human disease.

The committee offers analysis and insight into these areas

  • Monitoring of drug residues. The book provides a brief overview of how the FDA and USDA monitor drug residues in foods of animal origin and describes quality assurance programs initiated by the poultry, dairy, beef, and swine industries.
  • Antibiotic resistance. The committee reports what is known about this controversial problem and its potential effect on human health.

The volume also looks at how drug use may be minimized with new approaches in genetics, nutrition, and animal management. November

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