EXPLANATION OF THE 1996 FSIS NATIONAL RESIDUE PROGRAM

Introduction

The Food Safety and Inspection Service (FSIS) of the United States Department of Agriculture (USDA) is responsible for ensuring that USDA-inspected meat and poultry products are safe, wholesome, free of adulterating residues, and accurately labeled. As part of this responsibility, FSIS conducts the National Residue Program (NRP) to help prevent the marketing of animals containing unacceptable (violative) residues from pesticides, animal drugs, or potentially hazardous chemicals. The NRP collects samples of meat and poultry products at domestic slaughter establishments under FSIS and State inspection authority. These samples are then analyzed for violative residue concentrations. Violative residue concentrations are determined by reference to residue limits (tolerances or action levels) established by the Environmental Protection Agency (EPA) for pesticides and by the Food and Drug Administration (FDA) for animal drugs and environmental contaminants.

The NRP activities reported in this report cover monitoring and enforcement testing.

Monitoring

Monitoring involves the sampling of specified animal populations to provide information about the occurrence of residue violations on an annual, national basis. Compounds considered for inclusion in the National Residue Program generally have established residue limits - either tolerances or action levels. Residue limits pertinent to the 1996 NRP are listed in Appendix I.

Selection for monitoring is based on compound evaluations and the availability of laboratory methodology that is suitable for regulatory purposes. Monitoring information is obtained through a statistically based random selection of specimens of normal-appearing tissues from passed carcasses (healthy animals). Generally, for a specific slaughter class/compound pair, the number of specimens (300) chosen provides a 95% probability of detecting at least one violation when 1 percent of the animal population is violative (see Table on page 14). In addition to profile information, the results are used to identify producers or other entities marketing animals with violative concentrations of residues. When such producers subsequently offer animals for slaughter the animals may be subjected to enforcement testing until compliance is demonstrated.

Exceptions to the number of specimens selected are made for minor slaughter classes and for major slaughter classes in which problems are suspected; smaller sample sizes may be used in the former case, larger sample sizes in the latter. The information generated from monitoring is reviewed periodically to assist in the allocation of Agency resources. A total of 31,748 monitoring sample units were analyzed during 1996 from all classes of food-producing animals.

Enforcement Testing

Enforcement testing consists of the analysis of specimens obtained from individual animals or lots based on clinical signs or herd history. Testing is performed to detect individual animals with violative concentrations of residues. It is emphasized in problem (high prevalence) populations and used as a tool to prevent residues from entering the food supply. Testing frequently results from decisions by program employees based on regional guidelines or direct observations. It is also used to follow up on those who have been identified as marketing animals with violative concentrations of residues. A total of 235,495 enforcement testing samples were analyzed in 1996.

In-plant Tests

In-plant tests are a key part of the NRP. They provide a rapid screening method to detect the presence of residues at the plant level.

SOS, for Sulfa-On-Site, was implemented in April 1988 to test swine urine for sulfonamide residues. SOS is used in many of the largest swine slaughtering facilities. Laboratory confirmation of violations is required.

CAST, for Calf Antibiotic and Sulfonamide Test, is used to test bob veal calves (under 150 pounds and less than three weeks old). Prior to 1996, CAST did not require laboratory confirmation of the result; any violation found with CAST resulted in immediate condemnation of the calf. Beginning in 1996, any zone of inhibition measuring greater than 18 mm is sent to the laboratory for confirmation.

STOP, for Swab Test on Premises, was implemented in 1979 to detect the presence of antibiotic residues in kidney tissue. Originally developed for testing dairy cows, STOP is now used for a number of slaughter classes. Laboratory confirmation is required before the animal carcass is condemned. Certain STOP-positive samples are tested for both antibiotics and sulfonamides; the sulfonamide violations are reported with the STOP antibiotic violations.

Confirmed STOP-positive sample specimens with sulfonamide residues that have no established limits are considered violative in those slaughter classes for which they are not approved for use.

FAST, for Fast Antimicrobial Screen Test, quickly detects both antibiotic and sulfonamide drug residues in kidneys and livers and has proved to be a suitable replacement for CAST and STOP. Though FAST is capable of detecting sulfonamides, this test is significantly less sensitive that the SOS test. FAST was implemented in pilot plants in 1995. FAST has been extended to approximately 50 of the largest cow and bob veal slaughtering plants in 1996.

INTERPRETATION OF PROGRAM RESULTS

Sample Analyses/Violations

In the 1996 Residue Data Book, the main entries in the body of the table under compound or compound/class headings refer to analyses of sample units comprising tissues from an animal or several birds from the same production lot. The "Specific Violative Residues" sections presented in smaller type below the tables refer to the actual residues found.

The violations and positives reported in the tables giving the results for the 1996 residue program and in Appendix II represent the number of sample units. A sample unit is generally a single animal, except for poultry. A poultry sample unit is a composite of six birds taken from the same flock. For example, tissue from one animal analyzed by the Chlorinated Hydrocarbons (CHCs) and Organophosphates screening method could contain more than one violative residue from this compound class. In the table, this animal would be counted as a single violation. Below the tables, the specific violative residues are enumerated. In the example above, if two different CHCs were found to be violative in a single animal, both analytes would be listed in this section.

It should also be noted that many sample tissues are analyzed for more than one compound or compound class and are reported here as separate analyses under each relevant compound heading. Each analysis is reported and included in the total residue findings, even though the samples came from the same animal.

In addition, limits of quantitation and detection should be considered when interpreting residue levels and occurrences.

Aggregation of Data

Care must be taken when making statistical inferences from these data. The domestic monitoring sampling program is designed to detect, with a predetermined level of confidence, specific compounds in the designated slaughter classes. The sampling program is not designed to provide an estimate of an overall national percentage of violations for all chemical residues or slaughter classes tested. The data on violations reported here should not be summed across either slaughter class or compound with the intent of arriving at a single value to represent the percentage occurrence of violations over all the species that were tested. This mathematical operation will not produce a statistically valid estimate for the population, given the sample design in use.

Confidence Intervals

Within a slaughter class/compound pair, the results of the sampling may be considered as representative of that slaughter class population, since the sample selection procedure is designed to approximate the selection of a simple random sample of animals. The percentage of violations in each slaughter class/compound pair is a statistically valid estimate of the corresponding slaughter class population percentage. Therefore, the information presented includes these estimates of percentage of violations, along with appropriate confidence intervals. The two-sided 95% confidence intervals for the population percentage of violations are given (i.e., the probability is approximately 95% that the interval ranging from the lower bound through the upper bound will contain the true population value). The confidence intervals were computed using a binomial distribution.

A Note on Calf Nomenclature

This edition follows the usage of the 1989 and later editions of the NRPP. "Fancy calves" in the 1988 edition became "Formula-fed calves" in 1989; "Western calves" in the 1988 edition became "Heavy calves" in 1989.

Non-violative Positive Results

Appendix II displays, for monitoring and enforcement testing (excludes In-plant tests), those laboratory-confirmed residues that are within established limits. The results may include some Unidentified Microbial Inhibitors (UMI's), residues from antibacterial agents that are present but cannot be accurately identified.

Voluntary Inspection Program

Voluntary inspection and certification program are maintained for rabbits and ratites. Results from 1996 are presented in Appendix III.

RESULTS

1996 Summary

A low level of violative monitoring samples was detected in 1996, as has been found in previous sampling years. FSIS data indicate that the great majority of the 134.3 million head of livestock and 8.1 billion birds are free of violative residues when they are slaughtered in federally inspected plants.

In 1996 the FSIS monitoring program sampled and tested for seven classes of animal drug and pesticide compounds, comprising approximately 51 residues. Of the 31,748 monitoring analyses, 50 showed violative concentrations of residues. As noted earlier, the percentage of violations for all samples and all residues is not necessarily representative of the percentage that are violative in the livestock population as a whole. The percentage occurrence of violations or positive findings can be considered representative only within a slaughter class/compound pair.

In the 1996 monitoring program, the following violations were found: 17 sulfonamides, 14 antibiotics, seven chlorinated hydrocarbons and chlorinated organophosphates, six ivermectin, and six arsenic. Multiple antibiotic violations were found in at least one bob veal sample.

The majority of these violations detected in the monitoring program were from illegal levels of approved animal drugs, particularly sulfonamides and antibiotics used to prevent or treat bacterial infections. Most antibiotic and sulfonamide residue violations are confined to a relatively small percentage of livestock and poultry that make up the meat supply. The recurring reason for drug residue violations in livestock and poultry is an apparent failure to allow an adequate withdrawal time for the drugs to clear the animal's system. Detected illegal residues are usually concentrated in kidney, liver, or fat rather than muscle meat. The monitoring program focuses on kidney and liver tissues, since most FDA limits are established in these tissues.

SPECIFIC NATIONAL RESIDUE PROGRAM COMPOUNDS/CLASSES

Antibiotics

Fourteen antibiotic monitoring violations were found among 7,375 samples from all slaughter classes monitored for antibiotics. Multiple antibiotic violations were found in at least one bob veal calf sample.

CAST: 21,045 analyses were performed on bob veal calf samples in 1996, with 169 violative animals. (58,197 CAST samples were tested in 1995, with 848 violative specimens.)

STOP: 41,995 analyses were performed on samples from horses, cattle, sheep/lambs, goats, and ostriches in 1996, with 292 violations. (83,524 STOP samples were tested in 1995, with 888 violations.)

FAST: 156,078 analyses were performed in cattle, sheep, goats, swine, and other animals in 1996, with 1,024 violations. (68,139 FAST samples in cattle in 1995 resulted in 804 violations.)

Sulfonamides

Seventeen sulfonamide violations occurred among 7,824 samples from all slaughter classes monitored for sulfonamides. Bob calves had four sulfa violations, sows and boar/stags each had three, and lambs and market hogs each had two. One sulfa violation each occurred in non-formula fed veal, goats, and geese. The 17 sulfa violations included 14 sulfamethazine and three sulfadimethoxine. SOS testing produced 24 violative samples of 15,600 analyses in 1996.

Arsenicals

Arsenical compounds are used in food-producing animals primarily as growth promoters and to prevent bacterial enteritis. Of the 1,056 monitoring samples of poultry, three violations were detected in young chickens, and three violations were detected in young turkeys.

Chlorinated Hydrocarbons & Organophosphates

These chemicals are effective insecticides. Some of these compounds - such as DDT - are no longer marketed because of their extremely long half-life. Of the 7,409 monitoring samples, seven violative analyses were found in sample specimens from horses, steers, heavy calves, goats, boar and stags, and sows. Violative levels of dieldrin were found in a horse, a steer, and a boar/stag. Violative levels of chlordane and DDT were found respectively in a heavy calf and a goat. Two sows contained violative levels of mirex.

Halofuginone

Halofuginone prevents coccidiosis, a serious and potentially fatal parasitic infection that spreads rapidly among chickens and turkeys. No violations were found among the 1,196 monitoring samples taken in 1996. The following samples were analyzed: 472 young chickens, 213 mature chickens, 400 young turkeys, and 111 mature turkeys, for a total of 1196 analyses.

Ivermectin

Ivermectin is one of the most widely-sold anthelmintic drugs in the United States. It is active against a wide variety of parasites. Six of 3,327 samples in 1996 monitoring were violative: two in dairy cows, two in goats, and one each in bulls and heavy calves. Samples were taken from ten production classes.

Levamisole

Levamisole is a broad-spectrum anthelmintic that is active against the mature stages of the major gastrointestinal helminths and against mature and immature lung worms. It is approved for use in swine, non-lactating dairy cattle, and beef cattle. Withdrawal times vary from two to 19 days before slaughter depending on the slaughter class and dosage regimen. Of the 4,101 samples tested in the 1996 monitoring program, no violations were found in the 14 production classes sampled.

Beta-Agonists: Clenbuterol

Clenbuterol, a growth promotant, is not currently registered for any livestock use in the United States. Clenbuterol is also a -agonist and can cause increased heart rate, muscular tremors, headache, nausea, fever, and chills in people who have eaten the livers of animals that have been treated with clenbuterol. In Spain there were two oubreaks of illness in 1990 involving 135 people who had consumed clenbuterol-contaminated liver. Although no deaths have resulted so far, FDA is concerned that some individuals may be more sensitive to clenbuterol and may suffer more severe side effects. FDA and FSIS are therefore cooperating in a survey of fancy veal calves. It is known that in treated animals, clenbuterol persists far longer in retinal tissue than in other tissues. Eyeballs, livers, and muscle were collected; FDA analyzed the eyeballs with an ELISA screen. Livers were to be analyzed only if the eyeballs were found to contain clenbuterol. If clenbuterol were found in liver, then the corresponding muscle would be analyzed.

The FDA/FSIS project took place in 1996-1997; 499 eyeballs were analyzed. Only one eyeball gave a positive result with the ELISA screen, but the presence of clenbuterol could not be confirmed in this sample. FDA determined that this animal contained residues of fenoterol, another member of the -agonist class of compounds. The results of this project are given in Appendix IV. In addition, in 1996, the livers from 324 animals (mostly show animals) were analyzed. All the liver samples were negative for clenbuterol.

1996 Residue Program Species-specific Results

Appendix V contains the results of the National Residue Program in a species-specific format.

Contacts and Address for Comments:

The results of the domestic residue sampling programs were compiled by the Emerging Issues Branch, Chemistry and Toxicology Division, in the Office of Public Health and Science. Technical comments/questions about the residue program should be referred to the Chemistry and Toxicology Division. The telephone number is 202-501-7319.

Current address is:

FSIS, Office of Public Health and Science
Chemistry and Toxicology Division
6912 Franklin Court Suite
1400 Independence Avenue SW
Washington, D.C. 20250-3700

Acknowledgments:

Office of Public Health and Science
FSIS, USDA

Cindy Deyrup, PhD
David Soderberg
Emerging Issues Branch, CTD

Joann Hicks
Lily Chounlamountry
Science Information Branch, FHSD

July 1998