Food Additives & Contaminants: Part A, 2014 Vol. 31, No. 11, 1834–1839, http://dx.doi.org/10.1080/19440049.2014.962625

Determination of chloramphenicol residues in commercial chicken eggs in the Federal Capital Territory, Abuja, Nigeria Felix E. Mbodia*, P. Ngukua, E. Okolochab and J. Kabirb a

Nigeria Field Epidemiology & Laboratory Training Programme (NFELTP), Abuja, Nigeria; bDepartment of Veterinary Public Health & Preventive Medicine, Faculty of Veterinary Medicine, Ahmadu Bello University, Zaria, Nigeria (Received 10 March 2014; accepted 3 September 2014) The use of antibiotics in poultry can result in residues in eggs. The joint FAO/WHO committee recommended banning the use of chloramphenicol (CAP) in food animals due to its public health hazards of aplastic anaemia, leukaemia, allergy, antibacterial resistance and carcinogenicity. This paper determines the prevalence of CAP residues in chicken eggs and assesses the usage and awareness of its ban amongst poultry farmers in the Federal Capital Territory (FCT), Abuja, Nigeria. A cross-sectional survey of registered poultry farmers in FCT was conducted using questionnaires to determine CAP administration in poultry and awareness of its ban. Pooled egg samples were collected from each poultry farm surveyed and from randomly sampled government-owned markets in FCT. Source of eggs by state were identified by the marketer at the time of collection. Samples were analysed using an enzyme-linked immunosorbent assay (ELISA) technique for the presence of CAP, and prevalence was determined. Of 288 total pooled samples collected, 257 (89.2%) were from the markets and 31 (10.8%) were from poultry farms. A total of 20 (7%) pooled egg samples tested CAP-positive; market eggs originated from 15 (41%) states of the country. Of the market eggs, 16 (6.2%) pooled samples tested positive. Of eggs from poultry farms, four (12.9%) tested positive. Mean CAP concentrations in the positive samples ranged from 0.49 to 1.17 µg kg−1 (parts per billion). CAP use amongst poultry farmers in FCT was 75.5%; awareness of the CAP ban was 26.3%. Though 66% of veterinarians were unaware of a CAP ban, they were more likely to be aware than other poultry farmers (odds ratio (OR) = 1.4). Farm managers who use CAP were more likely to be aware of CAP ban than the farm managers not using CAP (OR = 5.5; p = 0.04). Establishing a drug residue surveillance and control program and enforcement of CAP legislation/regulation is needful to educate and prohibit the widespread CAP use amongst Nigerian poultry farmers. Keywords: CAP residues; chicken eggs; ELISA; FCT; Nigeria

Introduction Antibiotic use in poultry could result in residues in edible products of which chloramphenicol (CAP) is of particular concern because of its toxicity and non-dose-dependent fatal aplastic anaemia in humans (Olatoye et al. 2012). However, in most developing countries, including Nigeria, indiscriminate administration of antibiotics to food animals is a common practice due to unregulated distribution and access of livestock farmers to veterinary drugs on the open markets or over the counter without veterinary prescription and supervision (Dipeolu 2002). CAP is a broad-spectrum antibiotic that is active against both Gram-positive and -negative bacteria (Sorensen et al. 2003). In Nigeria, many poultry farmers use CAP to control poultry diseases because of its claimed efficacy (Omeiza et al. 2012). It has been used against Salmonellosis and other bacterial diseases of poultry (Olatoye et al. 2012). CAP residues in foods of animal origin are potential public health hazards, namely allergies, antibacterial resistance, carcinogenicity, genotoxicity, fetotoxicity, leukaemia, and reversible and irreversible *Corresponding author. Email: [email protected] © 2014 Taylor & Francis

dose-dependent aplastic anaemia (FAO/WHO 2004). Globally, aplastic anaemia affects one in 10 000–50 000 patients receiving a typical course of CAP therapy (Payne et al. 1999). Even low doses of administered CAP may result in residues in edible tissues from treated food-producing animals; therefore, consumers of milk, meat, aquaculture products, honey and eggs may be exposed to potentially harmful levels of CAP residues (Gallo et al. 2005). CAP also accounted for 25–30% of the total residues in eggs (Akhtar et al. 1996) and its residues can still be found at 1 ng g−1 in hen egg yolk 70 days after treatment (Arnold & Samogyi 1986). For CAP residues in meat, eggs, milk, aquaculture products and honey, the European Commission established a 0.30 ng g−1 minimum required performance limit to ensure the same level of consumer protection throughout the community (EC 2003). Due to concerns over its potential public health risks, coupled with the fact that the ADI and MRL could not be established, JECFA recommended banning the use of CAP

Food Additives & Contaminants: Part A in food-producing animals, globally. It is therefore considered a drug with an established zero tolerance (JECFA 2004). Although the Foods and Drug Decree of Nigeria, 1974 is a legal instrument that provides for residue avoidance in accordance with the recommendations of the FAO/ WHO Codex Alimentarius Commission, CAP ban for sale and use in food-producing animals is yet to be enforced in Nigeria. A number of different methods for determining CAP have been reported such as HPLC, GC, ELISA, and radio and enzyme immunoassay (RIA, EIA). Nonetheless, the methods using GC-MS for analysis required derivatisation of CAP, which lengthens the analysis time and may compromise analyte recoveries (Rocha Siqueira et al. 2009). Derivatisation techniques, in general, are not preferred for residue analysis because they are time-consuming and not reproducible at trace levels. Development of methods using microbiological, chemical (HPLC, GC) and immunological (EIA, RIA) techniques have led to the consequential lowering of the LOD in the matrices investigated by a factor of ≥ 1000 (Cerkvenik 2002). The ELISA method, however, has the advantages of quick assay time, no cross-reactivity of secondary antibody with components in the antigen sample, no health hazards compared with radio-immunoassays and its sensitivity is better than chromatographic methods. Preliminary studies suggested that CAP is among antibiotics frequently administered to poultry in Nigeria (Kabir et al. 2004; Omeiza et al. 2012). Hence, we surveyed commercial chicken eggs and poultry farmers to determine the presence of CAP residues in the eggs, its usage and the awareness of its ban amongst poultry farmers in the Federal Capital Territory (FCT), Abuja, Nigeria.

Materials and methods Study area The FCT, Abuja, was officially created on 12 December 1991 as Nigeria’s capital city. It is located in the centre of Nigeria and has a land area of 800 km2. The national population census conducted in 2006 puts the human population of the FCT at 1.4 million people (NBS 2006). The poultry population of the FCT is about 3.8 million (FAO 2004). Due to high demand for eggs in the FCT, there is high influx of commercial chicken eggs from other parts of Nigeria into the FCT. Administratively, the FCT consists of six area councils, namely Abaji, Kwali, Gwagwalada, Kuje, Bwari and Abuja Municipal.

Sampling technique A cross-sectional study was conducted. The sample size predetermined for this research was 288 pooled egg samples. (Ten eggs make a pooled sample. This was achieved by

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breaking 10 eggs, discarding the albumin, homogenising the yolks and taking 10 ml into a labelled test tube as one sample.) We took pooled egg samples from farms (31) and markets (257). We administered questionnaires to poultry farmers. A list of poultry farms registered in the FCT under the Avian Influenza Control Programme was obtained. One hundred farms were registered. Each farm was visited for enrolment: 57 were found to be operational and were recruited for the study. One questionnaire was administered to each of the 57 poultry farms to determine CAP usage and level of awareness on the regulatory status of CAP. Of the 57 farms visited, only 31 were at the egglaying stage, hence only 31 pooled egg samples from farms were collected. Stratified sampling of markets was first employed. FCT was divided into two strata: government-owned markets in Abuja city centre (50% proportionate to size) versus government-owned markets in satellite area councils’ headquarters (50% proportionate to size). Sampling of the markets was done using a computer generated table of random numbers. Three markets were randomly sampled from the Abuja city centre and three markets also were randomly sampled from the satellite area councils’ headquarters. A list of all the major egg marketers (full-time egg sellers) from each sampled market was obtained to serve as a sampling frame for eggs. A pooled sample of 10 eggs per marketer per state of origin was collected and recorded. Sampled markets were visited sequentially until the 257 pooled egg samples were obtained. Egg shell was thoroughly cleaned with cotton wool using 75% ethanol, broken at the taper ends to drain the albumen and 10 ml of the homogenised egg yolk were collected into capped test tubes, properly labelled and frozen, ready for laboratory analysis. The use of egg yolk as a representative sample for this analysis was due to its higher drug residue concentration (Kan & Petz 2000). Laboratory analysis Chloramphenicol ELISA kits sourced from AntibodiesOnline® Inc. (Atlanta, GA, USA) was employed for the laboratory analysis of the egg samples based on competitive enzyme immunoassay. The ELISA kit used was a 96well ELISA micro-plate: 12 strips with eight removable wells each. Six standards (controls) were included: 0, 0.05, 0.15, 0.45, 1.35 and 4.05 µg kg−1. Laboratory analysis was based on the manufacturer’s recommended protocol as follows. Homogenised sample (3 g) was weighed and 9 ml of acetonitrile solution were added and shaken for 5 min and centrifuged at 4000 r/min for 10 min. A total of 3 ml of the upper layer was transferred into a centrifuge tube and 3 ml of deionised water added, mixed thoroughly, then 4.5 ml of ethyl acetate added, mixed thoroughly for 5 min and centrifuged at 4000 r/min for 10 min. The organic

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phase (supernatant) was transferred into a new centrifuge tube and blown to dryness with nitrogen at 50°C. The dry residues were then dissolved in 1 ml of n-hexane, and 2 ml of the diluted re-dissolving solution were added, mixed thoroughly for 30 s, and centrifuged to remove n-hexane. A total of 50 µl was then taken for final analysis. All the necessary reagents from the kit were taken out and placed at RT for 30 min, shaken to mix evenly before use. A total of 40 ml of the concentrated washing buffer (20× concentrated) was diluted with distilled water at 1:19 to 800 ml for use. The micro-wells were numbered according to samples and standard solution. The concentrated antibody working solution was diluted with the redissolving solution at 1:10. A total of 50 µl of the sample or standard solution were added to separate wells; 50 µl of the diluted antibody working solution were added to each well, mixed gently by shaking the plate manually. The microplate was then sealed with the cover membrane and incubated at 25°C for 30 min. The liquid was poured off the microplate and washed with buffer at 250 µl/well four to five times for 15–30 s and flapped to dry with absorbent paper. A total of 100 µl enzyme conjugate were added into every well, sealed with cover membrane and incubated at 25°C for 30 min. A total of 50 µl of substrate A solution and 50 µl of substrate B solution were added into each well, mixed gently

Figure 1.

by shaking the plate manually and incubated at 25°C for 15 min in the dark for colour development. The colour intensity was inversely proportional to the CAP concentration in the sample. The sensitivity or LOD of the ELISA method was 0.1 µg kg−1, and the LOQ of 0.3 µg kg−1 was the cut-off value. The optical density (OD) values of the samples were read with an ELISA Plate Reader and the CAP concentrations were determined using the professional analysing software for the ELISA kit developed by Antibodies-Online Inc.

Statistical analysis Univariate analysis was carried out to obtain means, frequencies and proportions for data summary. Bivariate analysis was conducted using 2 × 2 (contingency) tables to examine the strength of associations (OR – odds ratio). Fischer’s exact (p) values were used for statistical significance and inferences.

Results Figure 1 shows a map of Nigeria with the distribution of the egg samples (and those that were CAP positive) from FCT markets and their states of origin. Eggs sampled from the markets originated from 15 (41%) out of 37 states in Nigeria, including the FCT. Tables 1 and 2 show the total

(colour online) Distribution of sources of CAP-positive eggs in FCT, Nigeria.

Food Additives & Contaminants: Part A number of egg sampled from markets (89.2%) and FCT farms (10.8%). Of the total of 288 pooled egg samples, 20 (7%) tested positive for CAP. Of the 20 samples that tested positive, 10 (50%) originated from Oyo State (south-west Nigeria). Of market eggs, 16 (6.2%) pooled samples tested positive. Of eggs from poultry farms, 4 (12.9%) tested positive. Mean CAP concentrations in the positive samples ranged from 0.49 to 1.17 µg kg−1 (Table 1).

Table 1. Nigeria.

ELISA test result by egg sample (source) in FCT,

Origin FCT States bordering FCT States not bordering FCT to the north States not bordering FCT to the south Total

Number of (pooled) samples, n = 288

Number of positive samples (mean CAP concentration, ppb)

Overall prevalence (%)

128 14

4 (1.17) 1 (0.69)

1.4 0.4

66

5 (0.49)

1.7

80

10 (0.78)

3.5

288

20

7.0

Table 2. ELISA test results of egg samples from farms and markets in FCT, Nigeria. Sample source Farmsa GWAC farms ABJAC farms AMAC farms BWAC farms KAC farms KWAC farms Subtotal Markets Garki modern market Wuse market Utako market Kwali market Gwagwalada market Kuje market Subtotal Grand total

Frequency of (pooled) samples (%), n = 288

ELISA result positive

ELISA result negative

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Table 3 shows the rate of CAP usage and awareness of CAP ban by poultry farmers. This study found that farmers not only were using three different brands of veterinary CAP preparations, but also were also using human CAP preparation for poultry. The three different branded veterinary CAP preparations used were N.C.O Mix® (43.9%), Neocloxin® (26.3%) and Tyfurchlor® (5.3%), bringing the total veterinary CAP usage to 75.5% and 8.8% human CAP usage. Table 4 shows the relationship between CAP usage and the ELISA test result. It is more likely (OR = 14.8, p = 0.01) to detect human CAP in egg samples by an ELISA test than the veterinary CAP preparations. Table 5 shows

Table 3. Usage and awareness of CAP amongst poultry farmers in FCT, Nigeria. Variable

Frequency (n = 57)

Proportion (%)

15 25 3

26.3 43.9 5.3

5 52

8.8 91.2

15 41

26.3 71.9

Usagea Neocloxin® N.C.O. Mix® Tyfurchlor® Use human CAP? Yes No Aware of CAP ban? Yes No

Note: aN.C.O. Mix® = neomycin, chloramphenicol and oxytetracycline; Neocloxin® = neomycin, chloramphenicol and oxytetracycline; Tyfurchlor® = tylosin, furazolidone and chloramphenicol.

Table 4. Relationship between CAP usage and residue containing eggs in FCT poultry farms, Nigeria. ELISA test (farms) positive

ELISA test (farms) negative

2 4 1 2

10 21 2 3

6 (2.1) 1 (0.3)

0 0

6 1

4 (1.4) 3 (1.0) 10 (3.5) 7 (2.4) 31 (10.7)

0 0 4 0 4

4 3 7 6 27

Neocloxin® N.C.O. Mix® Tyfurchlor® Human CAP

55 (19.1)

3

52

Table 5. Awareness of CAP ban for use in food-producing animals amongst respondents in FCT poultry farms, Nigeria.

43 (15.0) 57 (19.8) 34 (11.8) 36 (12.5)

6 5 1 1

37 52 33 35

Awareness, Awareness, yes no

32 (11.1) 257 (89.3) 288 (100)

0 16 20

32 241 268

Note: aABJAC, Abaji Area Council; AMAC, Abuja Municipal Area Council; BWAC, Bwari Area Council; GWAC, Gwagwalada Area Council; KAC, Kuje Area Council; KWAC, Kwali Area Council.

Use of n = 57

CAP,

Variable, n = 57 Farm owner Farm manager Farm veterinarian Othersa CAP using Farm managers a

OR p-value 8.3 5.7 7.8 14.8

0.05 0.06 0.1 0.01

OR

Fischer’s exact p-value

3 8 1 3

9 22 2 9

1.03 1.0 1.4 0.9

0.9 0.9 0.3 0.4

8

49

5.5

0.04

Note: Poultry attendants and supervisors.

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the relationship between the farmers and their awareness of the CAP ban. Awareness of the CAP ban was 26.3%. Although 66.6% of the farm veterinarians were not aware of the CAP ban, they were more likely (OR = 1.4) to be aware of the ban than other poultry farmers. Farm managers who use CAP were 5.5 times more likely to be aware of CAP ban than the farm managers not using CAP (p = 0.04). Discussion The outcome of this study revealed that CAP residues are present in commercial chicken eggs in poultry farms and markets in FCT. This implies the contravention of the ban on the use of CAP in food animals. The CAP prevalence (7%) in FCT is contributed by the influx of CAP-positive eggs (5.6%) from states bordering the FCT and beyond. This implies that CAP residues in chicken eggs have a nationwide spread in Nigeria. This nationwide occurrence of CAP residues poses an enormous health risk to Nigeria’s human population and therefore calls for a national drug residue surveillance and control programme. In most countries the total ban of CAP is in place with very few reports of CAP residue occurrence. In Slovenia, between 1991 and 2000, a survey of 1308 different animal tissue products including eggs showed CAP residues were determined (using GC) in only one milk sample with a prevalence of 0.1% (Cerkvenik 2002). This low prevalence results from the CAP residue monitoring and a consequence of the strict prohibition of this veterinary drug for food-producing animals, as well as a proper veterinary sanitary control of its residues in Slovenia. Similar studies by Olatoye et al. (2012) in Ibadan, Oyo State (south-west of FCT), and Omeiza et al. (2012) in Kaduna State (north of FCT) have also confirmed occurrences of CAP in chicken eggs with 25% and 0.7% prevalence respectively. Of the eggs that tested positive for CAP in this study, 50% originated from Oyo State (southwest of FCT). This confirms the findings of Olatoye et al. (2012) that there is high prevalence of CAP residues in poultry products in Ibadan. The frequency of occurrence of CAP residues showed that Kuje Area Council amongst the six area councils in the FCT recorded the highest. In fact it was only farms from Kuje Area Council that tested positive for CAP. This is not surprising because Kuje Area Council has the highest poultry (population) farms in FCT. A high density of farms increases the risk of spread of diseases between farms, leading to greater use of antimicrobials (Mohamed et al. 2012). Similar to this study, usage of CAP cuts across different geographical locations such as Ibadan, Nigeria (Olatoye et al. 2012), Kaduna, Nigeria (Omeiza et al. 2012), and Morogoro, Tanzania (Nonga et al. 2010). This usage even includes human CAP preparations as found in this study and that of Omeiza et al. (2012).

This may be due to lack of understanding by poultry farmers of the pharmacokinetics of CAP in chickens who erroneously believe that human CAP is as good or even better than veterinary CAP preparation and which leads to their abuse and indiscriminate use of these drugs. This implies a bilateral lack of effective control of both human and veterinary drugs, especially in Nigeria. For using CAP in food animals, an Iowa, Washington county, large animal (veterinary) practitioner in 1991 was sentenced to 12 months imprisonment, the costs of imprisonment, a US$15 000 fine and two years’ supervised release (FDA 1991). The conviction came after the trial, which was held in the US District Court for the Northern District of Iowa. It was established that the veterinarian acquired, processed, used, and dispensed CAP and other illegal animal drugs in his food animal practice. The trial also established that he had been aware of the prohibition against the use of CAP in food animals. In the same vein, if the Foods and Drugs Decree of Nigeria, 1974 were to be enforced, regulations concerning the use of CAP and other abused veterinary drugs would be adhered to. This will go a long a way to protect public health in Nigeria. In the survey of poultry farmers rearing commercial layers in Kaduna State, Nigeria (Omeiza et al. 2012), only 26.7% of respondent farmers were aware that CAP was one of the drugs that is not recommended for use in food animals. This agrees with the findings in this research whereby only 26.3% of the poultry farmers were aware that CAP is not recommended for use in food animals. It was also found in this study that poultry attendants specifically are less likely (OR = 0.9) to be aware of the CAP ban for use in food-producing animals. There is poor perception of the possible effects of antimicrobial residues on human health in Nigeria. This has highlighted the low level of awareness of legislation that governs the application of drugs (especially CAP) in poultry (Omeiza et al. 2012). This lack of awareness amongst poultry farmers on the ban of CAP for use in food animals is of great public health concern and importance. Consequently, WHO recommends effective reporting of residues in foods of animal origin meant for human consumption, especially in developing nations where poor perception of residues among livestock farmers is common (Cannavan 2004). Conclusion Findings from this study showed that CAP residues were present in commercial chicken eggs destined for human consumption in the FCT, Abuja, Nigeria. These residuecontaining eggs were both from poultry farms within FCT and other states of Nigeria, and most poultry farmers in FCT using both human and veterinary CAP preparations were unaware of the FAO/WHO global ban on its use in food-producing animals. These results indicate that egg consumers in FCT (and other parts of Nigeria) are exposed

Food Additives & Contaminants: Part A to health hazards associated with CAP residues and this can jeopardise international egg trade from Nigeria. The National Agency for Food, Drug Administration and Control (NAFDAC) should enforce the food and drug decree (1974) that provides for residue avoidance in accordance with the recommendations of FAO/WHO Codex Alimentarius Commission towards implementing total ban of CAP use in food animals in Nigeria. The Veterinary Council of Nigeria should insist on a continuing education programme for veterinarians. In turn, veterinarians should educate poultry farmers and livestock extension workers on best practices for the use of veterinary drugs, while emphasising on alternative management options such as vaccinations, environmental sanitation and disease containment, which would decrease the use of antibiotics that could reduce the frequency of antimicrobial drug residues in poultry production. Funding This work was financially supported by the Nigeria Field Epidemiology & Laboratory Training Programme and with the technical assistance of Mallam Yahuza Suleiman of the Department of Veterinary Public Health and Preventive Medicine, Ahmadu Bello University, Zaria, Nigeria.

References Akhtar MH, ElSooud KA, Shehata AM, -ul-Haq A. 1996. Fate and residues of 14C-chloramphenicol in laying chickens. J Environ Sci Health: Part B. 31:1061–1084. Arnold D, Samogyi A. 1986. Chloramphenicol residues in edible tissues of food animals. Proceedings of the 2nd world congress. Food-borne Infections and Intoxications, Vol. 2. Berlin: Institute of Veterinary Medicine – Robert von Ostertag-Institute; p. 832–836. Cannavan A. 2004. Capacity building for veterinary drug monitoring programs in developing countries. In: FAO/WHO technical workshop on residues of veterinary drugs without ADI/MRL [Internet]. [cited 2014 Feb 1]. Available from: www.who.int/ipcs/events/2004/en/bangkok2004_report2.pdf Cerkvenik V. 2002. Analysis and monitoring of chloramphenicol residues in food of animal origin in Slovenia from 1991 to 2000. Food Addit Contam. 19:357–367. Dipeolu MA. 2002. Residues of tetracycline antibiotic in marketed goats and pigs in Lagos and Ogun States of Nigeria. Trop J Anim Sci. 5:47–51.

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[EC] European Commission. 2003. Decision 2003/181/EC. OJEC. Mar 13;L71:17–18. FAO. 2004. Small scale poultry production [Internet]. [cited 2014 Feb 1]. Available from: http://www.fao.org/ag/ AGAInfo/resources/documents/brief_notes/BNpoultry5.pdf FAO/WHO Technical Workshop. 2004. Residues of veterinary drugs without ADI/MRL, Aug 24–26; Bangkok; p. 175 FDA vet. 1991. Veterinarian sentenced on chloramphenicol charge. J Am Vet Med Assoc. 199:317. Gallo P, Nasi A, Vinci F, Guadagnuolo G, Brambilla G, Fiori M, Serpe L. 2005. Rapid Commun Mass Spectrom. 19:574–579. JECFA. 2004. Joint FAO/WHO technical workshop on residues of veterinary drugs without ADI/MRL; Aug; Bangkok; p. 31, Annex IV. Kabir J, Umoh VJ, Audu-okoh E, Umoh JU, Kwaga JKP. 2004. Veterinary drug use in poultry farms and determination of antimicrobial drug residues in commercial eggs and slaughtered chicken in Kaduna State, Nigeria. Food Contr. 15:99– 105. Kan CA, Petz M. 2000. Residues of veterinary drugs in eggs and their distribution between yolk and white. J Agric Food Chem. 48:6397–6403. Mohamed M, Jackie P, Shahn B, Alexander R, Bruce G. 2012. A survey of antimicrobial residues in table eggs in Khartoum State, Sudan, 2007–2008. Onderstepoort J Vet Res. 79:1–9. [NSB] National Bureau of Statistics. 2006. Official Gazatte, Legal Notice on Publication of the Details of the Breakdown of the National and State Provisional Totals 2006 Census [Internet]. [cited 2014 Feb 1]. Available from: http://www.nigerianstat. gov.ng Nonga HE, Simon C, Karimuribo ED, Mdegela RH. 2010. Assessment of antimicrobial usage and residues in commercial chicken eggs from smallholder poultry keepers in Morogoro municipality, Tanzania. Zoonoses Public Hlth. 57:339–344. Olatoye IO, Oyelakin EF, Adeyemi IG, Call DR. 2012. Chloramphenicol use and prevalence of its residues in broiler chickens and eggs in Ibadan, Nigeria. NVJ. 33:4. Omeiza GK, Idowu OF, Junaidu K, Mohammed M, Hajara I. 2012. Response of Nigerian farmers to a questionnaire on chloramphenicol application in commercial layers. Vet Ital. 48:87–93. Payne MA, Baynes RE, Sundlof SE, Craigmill A, Alistair I, Riviere JE. 1999. Drugs prohibited from extralabel use in food animals. JAVMA. 215:1. Rocha Siqueira SR, Luiz Donato J, de Nucci G, Reyes Reyes FG. 2009. A high-throughput method for determining chloramphenicol residues in poultry, egg, shrimp, fish, swine and bovine using LC-ESI-MS/MS. J Sep Sci. 32:4012–4019. Sorensen LK, Elbek TH, Hansen H. 2003. Determination of CAP in bovine milk by liquid chromatography/tandem mass spectrometry. J AOAC Int. 86:703–706.

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