Occurrence of antimicrobial residues in raw cow milk and potential public health Implications from Morogoro and Monduli, Tanzania

Abstract

Antimicrobial residues in cow’s milk pose significant public health risks due to their potential adverse effects, including toxicity, allergic reactions, and the promotion of antimicrobial resistance. This threat is particularly pronounced in low- and middle-income countries, where veterinary drug use is poorly regulated and monitoring systems are limited. This cross-sectional study investigated the presence of antibiotic residues and associated risk factors in raw cow’s milk from Morogoro Municipality and Monduli District. A total of 63 smallholder livestock farmers, 30 from Monduli and 33 from Morogoro were interviewed to gather information on cattle management, disease control, and antimicrobial usage. Concurrently, 100 ml pooled raw milk samples were collected from each farm and analyzed for seven types of antimicrobial residues namely Oxytetracycline (OTC), Chlortetracycline, Ciprofloxacin, Trimethoprim, Amoxicillin, Sulfadiazine and Sulfamethoxazole using High Performance Liquid Chromatography with Ultraviolet-Visible Spectroscopy (HPLC-UV/VIS). The results indicated that oxytetracycline (OTC) was the sole antimicrobial residue detected, with a prevalence of 39.7% and a mean (standard deviation - SD) concentration of 99.9 ± 16 µg/L. Notably, 44% of positive samples exceeded the Codex Alimentarius Commission (CAC) Maximum Residue Limit (MRL) of 100 µg/L, with most non-compliant samples originating from Morogoro Municipality. Extensive grazing systems and routine use of OTC for disease treatment were significantly associated with residue occurrence. These findings underscore the widespread and unregulated use of antibiotics in Tanzanian smallholder livestock systems and highlight the urgent need for farmer education, strengthened veterinary oversight, and enforcement of withdrawal periods to safeguard milk safety and protect public health.