Detection and determination of Oxytetracycline and Penicillin G antibiotic residue levels in bovine bulk milk from Nazareth dairy farms, Ethiopia

A cross-sectional study was conducted between October 2007 and May 2008 to detect and determine oxytetracycline and penicillin G residue levels in bulk milk of cows in Nazareth dairy farms. A total of 400 bulk milk samples were randomly collected. All samples were qualitatively screened for antibiotic residues by Delvotest SP assay. Questionnaire survey was carried out by personal interviews with some of the dairy farm owners in Delvotest positive farms (cases) and Delvotest negative farms (controls) to identify various risk factors for the occurrence of antibiotic residue in milk. Farm management practices, disease conditions and treatment factors have been identified as the main risk factors. Concentration of Oxytetracycline and Penicillin G in the positive samples was determined by High Performance Liquid Chromatography. Out of 400 samples analyzed for antibiotic residue, 48 (12 %) milk samples were positive for antibiotic residues. The mean residue level of oxytetracycline was 125.25μg/l and that of penicillin G was 4.52 μg/l. Concentrations of oxytetracycline and penicillin G in all samples were between ranges of 45 -192 μg/l and 0-28 μg/l, respectively. The antibiotic residue positive samples which showed residues of oxytetracycline above the WTO/FAO/ CAC established maximum residue limit of 100μg/l were 40 (83.33%). For penicillin G, the number of samples above the maximum residue limit of 4μg/l, were 8 (16.66%). In conclusion, this study revealed that oxytetracycline and penicillin G were imprudently used in dairy farms of the study area.Keywords: Delvotest SP, High Performance Liquid Chromatography, Milk, Oxytetracycline, Penicillin G, Residu