Introduction

The primary purpose of veterinary drugs, biologics and pesticide chemicals is to safeguard the health and welfare of animals^4. Antibiotics used for these purposes can occur as residues for some time in these animals before they are excreted. A chemical residue is either the parent compound or its metabolites that may deposit accumulate or otherwise be stored within the cells, tissues, organs or edible products of animals following it use to prevent, control or treat animal disease or to enhance production ¹⁴. Drugs are the most frequently detected chemical residues, the overwhelming majority of which are antimicrobials ¹⁵ and, are commonly used drugs in veterinary practice in Nigeria¹. The concerns over drug residues are public health and economically related ¹⁵. Drug and pesticide residue concerns are among the reasons adduced for Africa’s denial into European and American livestock markets¹. The palatability, aroma and quality of meat could be affected by drug residues. Residues of food animal drugs threaten human health by been acutely or cumulatively allergenic, organotoxic, mutagenic, teratogenic or carcinogenic ¹. Violative residues of penicillin are the most frequently cited causes of allergic reaction in persons that consume animal products containing residues. Many other drugs including tetracyclines, sulphonamides and aminoglycosides can also cause allergic reaction ¹⁵. Aminoglycosides (e.g. streptomycin) can cause varying degree of nephrotoxicity and ototoxicity, a potential to cause muscular paralysis, a tubacurare like activity on respiratory muscles and death. Antimicrobial residues were detected in slaughtered cattle ^{6, 9, 15} goat and pig ⁵ and in chicken ⁷ in some different parts of Nigeria. Drug resistance appears to be the most important hazard of drug residues in the country ⁶. The resistant bacteria could then cause disease that is difficult to treat in humans and may also transfer the resistant gene to some other human pathogens ^{2, 8}. Hitherto, withdrawal period are not observed and there is no programme for monitoring/surveillance of veterinary drug residues as such, a number of slaughtered cattle may contain an undetermined magnitude of residue ^{1, 6, 12}. Sokoto state is a major source of beef in Nigeria. The risk to adverse effects of drug residue and drug resistance could be higher if the trend of misuse and abuse of drugs is left unchecked. Hence, the present study attempted to determine the presence of antibiotic residue in meat from slaughtered cattle in Sokoto, Nigeria.

Materials and Methods

Study area

Sampling

Preparation of inoculums and media

Technique

Results

Table 1 shows a total of 22(44%) slaughtered cattle positive for the presence of antibacterial substances. Out of these, the liver of 16(32%) slaughtered cattle was found positive while, both liver and kidneys of 6(12%) slaughtered cattle tested positive. However, base on the pH to which meat sample was found positive, presumptively, penicillin (14%) is the leading antibiotic followed by tetracycline (8%) and streptomycin (4%) in samples positive on a single plate. For samples with the multiple antibiotic residues: 8% contain tetracycline, streptomycin and penicillin, 4% tetracycline and streptomycin, 1% tetracycline and penicillin and, 4% penicillin and streptomycin.

Figure 1

Discussion

The issue of veterinary drug residues in animal derived food has become increasingly important in many developing countries ⁴. The presence of antibiotic residues in liver and kidney is similar to other findings in Nigeria ^{5, 6, 7, 9, 12}. However, these researches detected single antibiotic. The result of this study indicates the presence of multiple antibiotic residues and that penicillin, tetracycline and streptomycin in order frequency are commonly use or misuse drugs in cattle in Sokoto. Antibiotic residues were found more in the liver (44%) than in the kidney (12%). This could suggest that most samples were taken at the time when drugs were been metabolised in the liver not yet at the stage of clearance by the kidney. Invariably, antibiotics are most often administered close to the time of slaughter. The result also shows higher rate (44%) of antimicrobials than previous works done by Oboegbulem and Fedelis (1996), Kabir et al, (2001) and, Dipeolu and Alonge (2002) with prevalence of 0.24%, 7.4%, and 16.7% in slaughtered cattle respectively. Therefore, in Sokoto, antibiotics are used but often more misused than areas were other works were conducted in Nigeria (southwest: Dipeolu, 2002; Dipeolu and Alonge, 2002; east: Oboegbulem and Fedelis, 1996 and north central: Kabir et al, 2001) with resultant higher antibiotic residues. There might be a general increase in the abuse of veterinary drugs in the country. Withdrawal period is likely being observed more in those areas than in Sokoto or that these drugs are more commonly used here singly or in combination. It is likely that some cattle treated in Sokoto excrete the pharmacologically active compound during transit to, with resultant less antibiotic residues in southwest, eastern and north central Nigeria.

The zone of inhibition found between two pieces of liver on one of the plates could be due to synergism (from synergistic drugs e.g penicillin and streptomycin) or probably a reflection of high concentration of single inhibitory substance. Synergism occurs when the pharmacologic effect of interaction between two drugs exceeds additive effect of concurrent administration ¹¹.

The presence of antibiotic residues in meat is a serious problem that is yet to be addressed in developing countries like Nigeria where safety of food regarding drug residue is highly questionable. The multi antibiotic residues detected in meat from slaughtered cattle intended for sale to the human populace in Sokoto could be attributed to irrational use of drugs in food animals consequent to lack of regulatory system for veterinary drug use and control as observed previously¹. In addition stakeholders involved do not adhere to withdrawal period. Non adherence to withdrawal periods is the major cause of chemical residues¹⁴. To date there have been only few studies to determine the lowest dose of antibiotic required to perturb the normal human flora ¹⁵. It is therefore safer to consider any amount of drug residue significant. This necessitates that all effort including awareness creation, observance of withdrawal period, effective surveillance, monitoring and control on the use of veterinary drugs to prevent drug residues in animal derived products be employed.

Figure 2

Acknowledgements

The authors wish to acknowledge Prof. S.I Oboegbulem and Dr. Sati Samuel (NVRI Vom) for their assistance in sourcing the test bacteria. Dr A. A. Magaji, Dr. A.T Elsa and Dr. M.D Salihu were highly supportive. We are so grateful to Mal. Lawal Usman (Microbiology Unit, UDUTH) and Mal Nata’ala (School of Med. Lab Sci, UDUS) for assisting in the laboratory work.