Surveys on Antimicrobial Drug Residues in Slaughtered Cattle and Chicken in Nigeria
Chapter One
Objectives of the study
The main goal of this project was to;
- Determine the occurrence and concentration of drug residues in body parts (liver, kidney and muscle tissue) of chicken and cattle and cattle
- Compare the levels of residues with the World Health Organization (WHO)/Food and Agriculture Organization (FAO) Maximum Residue Limits (MRLs).
- Model toxic indexes due to consumption of chicken and cattle and cattle base on the concentrations of the residues present.
CHAPTER TWO
REVIEW OF LITERATURE
Antimicrobial drugs and antimicrobial drug residues
The generic term ―antimicrobial drugs‖ covers a broad variety of classes of chemical compounds. Antimicrobial drugs are any substances administered to food-producing animals for diagnostic, therapeutic, or prophylactic purposes as well as for modification of physiological functions or behavior (Jensen et al., 2003). They are biologically active substances designed to harm organisms such as bacteria, viruses, and parasites. Obviously, antimicrobial drugs are potentially hazardous to micro-organisms such as bacteria in the environment (Butaye et al., 2003; Jensen, et al., 2003; Toldra & Reig, 2006). The major concerns in antimicrobial drug usage are the presence of harmful residues that may be introduced into the human food chain (Dowling, 2012).
Residues are compounds present in edible tissues of the target animal that result from the use of a xenobiotic sustained (a chemical which is found in an organism but which is not normally produced or expected to be present in it or substances which are present in much higher concentrations than are usual), including its metabolites, or any other substances formed in or on food due to use of the chemical (El-Kholy & Kemppainen, 2005). Therefore, residues of antimicrobial drug are the remains of the administered drug, their metabolites or impurities of the drug left in the animals or food chain as a result of the drug usage. In other words they are the traces of antimicrobial drugs and their derivatives which can be found in food products of animal origin (Kumar, 2010).
Babapour et al., (2012), defined antimicrobial drug residues as the very small amounts of veterinary medicines that can remain in animal products and therefore make their way into the food chain. These include any degradation products, which are the result of the medicine breaking down.
Uses of antimicrobial drugs
Antimicrobial drugs play essential role in poultry production. They are generally used in farm animals for therapeutic and prophylactic purposes and they include a large number of different types of compounds which can be administered in the feed or in the drinking water. They are used to prevent and control infectious and non-infectious diseases, assist in reducing stress due to environmental changes, vaccination, debeaking and other management practices (Kabir et al., 2004). In addition, antimicrobial drugs are given in cases of disease, for rehydration or to prevent losses during transportation, enhance feed efficiency, promote animal growth, and improve productivity (Kao et al., 2001). Many of the antibiotics used in treating bacterial infections in humans also have veterinary applications (Kennedy et al., 2008).
Improper or illegal use of antimicrobial drugs
According to Dowling, (2012), a number of situations contribute to the improper use of licensed products. These include poor treatment records or failure to recognize treated animals and use of a drug other than as described on the product label. Residues occur chiefly by not observing sufficient withdrawal periods before slaughtering the animals. As long as a licensed drug is used in accordance with its product license and withdrawal periods respected drug residues should not occur in human food at concentrations exceeding the maximum residue limits.
CHAPTER THREE
MATERIALS AND METHODS
- Sampling
- Sample Collection
A total of 180 birds were slaughtered and 540 samples were obtained from the liver, kidney and muscles from each bird for veterinary residue analysis from the various poultry farms in and around Uyo. The samples were stored in refrigerator at 4oC until the time of analysis.
Sampling procedure
Birds were collected randomly from each poultry house (housing unit) from the farms on three different occasions from three different farms in each locality/town in 2 batches. The sampling was based on the assumption that mass treatment is the method of choice when treating layers and therefore antimicrobial residues should be equally distributed in all birds in the house at a specific time. Each periodic sample collection was done as a separate scheme as it was difficult to re-sample the same farm in different period for several seasons.
Sample handling and preservation
Each sample (kidney, liver and muscle) was labeled with a permanent marker and date of collection, farm origin and the farm number was clearly stated. The samples were transported in a cooled storage container below room temperature and were processed within 72 hours of collection. The samples were stored in a freezer (below 4 OC) until finally processed/analyzed.
Chemicals and Reagents
Chemicals
Anhydrous potassium dihydrogen phosphate (KH2PO4) HPLC grade (Fizmerk Chemicals, India), Methanol HPLC grade (Fisher Scientific, UK), Acetonitrile HPLC grade (Fisher Scientific, UK), Hexane, HPLC grade, (Fisher Scientific, UK). All other chemical reagents were of analytical grade.
CHAPTER FOUR
RESULTS AND DISCUSSION
Preparation of calibration curve
To determine the amount of the multi-residues in the liver, kidney and muscle samples, a standard calibration curve for all the eight drugs was obtained by running a mixed standard solution on HPLC and then plotting peak areas against concentrations.
Linearity was evaluated through the correlation coefficient which was ≥ 0.9991. The correlation coefficient, intercept and slope of calibration curve were calculated and to determine the limit of detection (0.01 µg/kg) and the limit of quantification (0.03 µg/kg).
CHAPTER FIVE
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
In conclusion, this study shows that there were antimicrobial drugs residues present in all the five farms visited. The concentrations of levamisole and albendazole residues mostly exceeded the recommended FAO/WHO MRLs, whiles others like tiamulin, piperazine and sulphamethoxazole were far below recommended FAO/WHO MRLs and the rest were below the limit of detection or were not found or might have been metabolized in to different compounds. Chloramphenicol was most frequently detected antimicrobial drug residue.
Most of the antimicrobial drug residues were concentrated in the liver and followed by the kidney and finally in the muscle sample. Levamisole presents posses a higher risk of exposure to the consumers as their mean concentrations mostly exceeded the MRLs.
After several interactions with the farmers, we got to know that all the farmers did not observe the withdrawal period of the antimicrobial drugs before they are administered to the birds and finally sell them out to the consumers. Again, some of them do not strictly go by the prescriptions on the label which may be attributed to illiteracy or because frequent uses of the drugs. Occurrence of Antimicrobial drug residues in edible animal tissues is a global problem.
Chloramphenicol which was frequently used in poultry farms in Nigeria and residues present in meat and eggs may be injurious to human health. Most of the chloramphenicol residues exceeded the ADI. In view of all these circumstances, foods of animal origin must be monitored for the presence of antimicrobial drug residues. This result indicates that, consumers are predisposed to health hazards and hinders international meat trade from Nigeria.
Recommendations for further development
Efforts are, needed on the part of the national authorities, Non-Governmental Organizations and Industry to control the problem of residual drugs in chicken, in Nigeria.
To this end the following steps are recommended.
- Farmers should be made to observe the withdrawal period of the antimicrobial drug This can be achieved by taking sample of the birds for analysis before they are allowed to be sold to the public.
- Monitoring laboratories must be set up throughout Nigeria to control drugs residues in eggs, meat and other food products sold to the populace.
- There should be legislation to control the indiscriminate use of antimicrobial drugs and infrastructure for its enforcement.
- There are currently insufficient data in Nigeria to support a national diet
Additional information from all the regions in Nigeria would allow a more representative model diet. With more national data available, the potential for a regional diet approach could be explored in the future.
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