Epidemiology of bovine mastitis and isolation of Escherichia coli and Staphylococcus aureus in dairy farms of Central Ethiopia

Bovine mastitis remains one of the most economically important diseases affecting dairy production worldwide, particularly in developing countries such as Ethiopia, where limitations in farm management, veterinary services, and disease monitoring exacerbate its impact. In central Ethiopia, integrated studies that simultaneously address epidemiology, bacteriology, and farm management practices are limited. This study aimed to assess the prevalence, bacteriological profile, farm management practices, and associated risk factors of bovine mastitis in selected dairy farms of Asella, Adama, and Bishoftu. A cross-sectional study was conducted on 371 lactating dairy cows selected from 37 dairy farms in the three study areas. Data were collected using structured questionnaires, on-farm observations, clinical examination, and laboratory analysis. Subclinical mastitis was screened using the California Mastitis Test (CMT), and milk samples from clinical mastitis and CMT-positive cases were subjected to standard bacteriological culture with ATCC reference control strain for isolation and identification of Escherichia coli (E.coli) and Staphylococcus aureus ( S.aureus) . Descriptive statistics were used to summarize the data, while Chi-square tests and multivariable logistic regression analyses were employed to identify associations between mastitis occurrence and potential risk factors. The overall prevalence of mastitis was 48.2%, with subclinical mastitis accounting for 44.2% and clinical mastitis for 4.0% of cases. Prevalence varied across study areas, with the highest recorded in Asella (58.0%), followed by Bishoftu (45.1%) and Adama (41.5%). Bacteriological analysis identified E.coli (29.4%) and S.aureus (27.0%) as the predominant pathogens, indicating the involvement of both environmental and contagious sources of infection. Reproductive history was the only factor significantly associated with mastitis ( p < 0.05; adjusted OR = 1.92; 95% CI: 1.00–3.68), while other host-related factors showed no significant association. Bovine mastitis is highly prevalent in the study areas, predominantly in its subclinical form. The significant association with reproductive history further highlights the need for integrated herd health management. Implementation of routine screening, improvement of milking hygiene and housing sanitation, and strengthening of farmer awareness and veterinary support services are essential to reduce the burden of mastitis and improve dairy productivity in central Ethiopia.