Determination of antimicrobial residue concentration levels in raw cow’s milk from dairy farms in Mvomero district, Tanzania

Background Veterinary antibiotics are essential for maintaining dairy cow health and preventing infections. However, improper use can leave residues in milk, which may pose public health risks. Understanding the occurrence of these residues and their potential impact on consumers is critical for safe milk production. This study determined the residue concentration levels and potential health risks of oxytetracycline, tetracycline, and tylosin residues in raw cow milk in Mvomero district, Tanzania. Methods A cross-sectional study was conducted in Dakawa and Mtibwa wards of Mvomero district, where raw cow milk samples were collected. Samples were first screened for antimicrobial residues using an inhibition assay and confirmed through High-Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS/MS). Residue concentrations were compared against the Maximum Residue Limits (MRLs) established by the Codex Alimentarius Commission, specifically those outlined in the Codex Alimentarius MRLs for Veterinary Drugs in Foods (CXM 2-2018) [1]. Also reference was made to national standards, including guidelines from the Tanzania Medicines and Medical Devices Authority and the Ministry of Livestock and Fisheries Tanzania [2], [3]. Human health risk was assessed using Hazard Quotient (HQ) based on the estimated daily intake [4], [5] . Results Out of the 380 raw cow milk samples screened using a microbial inhibition assay, 36 (9.5%) tested positive for antimicrobial residues. Confirmatory HPLC-MS/MS analysis of the 36 positive samples and 16 randomly selected negative samples revealed that OTC had the highest mean concentration (95.37 ± 12.51 mg/kg), followed by TTC (0.63 ± 0.07 mg/kg) and tylosin (0.23 ± 0.06 mg/kg). Residue levels of oxytetracycline and tetracycline generally exceeded the 100 µg/kg MRLs, while only 16 of the samples exceeded the permissible limits for tylosin. The estimated daily intake (EDI) values were 0.054, 0.0004, and 0.0001 mg/kg body weight/day for oxytetracycline, tetracycline, and tylosin, respectively, with corresponding Hazard Quotient (HQ) values of 1.80, 0.01, and 0.00. These findings indicate a potential health risk associated with oxytetracycline exposure through milk consumption, whereas tetracycline and tylosin are unlikely to pose significant chronic health risks at average intake levels. However, prolonged exposure to antimicrobial residues may contribute to antimicrobial resistance and long-term public health concerns. Conclusion Findings from this study highlight critical gaps in antimicrobial use practices and regulatory compliance within dairy production systems that may compromise milk safety and consumer health. Strengthening antimicrobial stewardship, improving farmer awareness on responsible drug use, adherence to withdrawal periods, and enforcing routine residue monitoring are essential to ensure the safety of milk and milk products and to mitigate the growing public health threat associated with antimicrobial resistance.