Prevalence of bovine mastitis and antibiotic susceptibility patterns of bacterial isolates in the Jaffna District, Sri Lanka.

BACKGROUND: Bovine mastitis is one of the most economically important infectious diseases affecting the global dairy industry. In the Jaffna district of Northern Sri Lanka, information on mastitis prevalence, bacterial aetiology, and antimicrobial resistance remains limited, constraining evidence-based disease management. OBJECTIVES: To determine the California Mastitis Test (CMT)-based prevalence of bovine mastitis in the Jaffna district, identify causative bacterial pathogens, evaluate antibiotic susceptibility patterns, and assess farm-level risk factors associated with mastitis occurrence. METHODS: A cross-sectional study was conducted from April to September 2024 across all 15 veterinary ranges of Jaffna district. A total of 200 milk samples from lactating dairy cattle were screened using the CMT. Positive samples were cultured, and bacterial isolates were identified through Gram staining and standard biochemical tests. Antibiotic susceptibility testing was performed using the Kirby-Bauer disk diffusion method against eight antibiotics following CLSI (2021) guidelines, and Multiple Antibiotic Resistance (MAR) indices were calculated. A structured questionnaire administered to 200 farmers collected data on management, breed, hygiene, and milking practices. Associations between risk factors and mastitis occurrence were analysed using chi-square tests and binary logistic regression. RESULTS: The overall prevalence of bovine mastitis was 10.0% (20/200), with all CMT-positive samples yielding bacterial growth. Staphylococcus aureus was the predominant isolate (50%), followed by Streptococcus agalactiae (30%), Escherichia coli (10%), and Klebsiella spp. (10%). Enrofloxacin showed the highest susceptibility (90%; MAR = 0.14), followed by Doxycycline (60%) and Ciprofloxacin (55%), whereas Oxytetracycline exhibited the lowest efficacy (15%; MAR = 0.45). Semi-intensive farming (aOR = 1.72; p = 0.05), European crossbred cattle (aOR = 3.12; p < 0.05), milk yield >10 L/day (aOR = 2.45; p = 0.036), absence of post-milking teat dipping (aOR = 2.67; p < 0.05), and non-use of gloves during milking (aOR = 2.90; p < 0.05) were significant risk factors. CONCLUSION: Bovine mastitis remains a significant challenge in Jaffna district, with S. aureus as the dominant pathogen. Enrofloxacin was the most effective antibiotic, while high resistance to Oxytetracycline highlights concerns regarding antimicrobial resistance. Improved milking hygiene and antibiogram-guided treatment strategies are recommended.