Prevalence of Bovine Mastitis and Isolation of Staphylococcus aureus from Cow Milk in Dessie Town, Northeast Ethiopia

Abstract Background: Bovine mastitis remains one of the most prevalent and economically significant diseases affecting dairy cattle worldwide. In Ethiopia, limited data exist on its prevalence, associated risk factors, and causative pathogens in emerging dairy farms such as Dessie Town. This study aimed to determine the prevalence of bovine mastitis, identify associated risk factors, and isolate Staphylococcus aureus from mastitic milk samples in Dessie Town, Northeast Ethiopia. Methods: A cross-sectional study was conducted on 304 lactating dairy cows across smallholder farms and semi-intensive farms. Clinical examination and the California mastitis test (CMT) were used to detect clinical and subclinical mastitis, respectively. Risk factors were assessed via structured questionnaires and analysed through univariable and multivariable logistic regression. A bacteriological analysis of 322 mastitic milk samples was performed for the isolation of Staphylococcus aureus via standard microbiological techniques. Results: The cow-level prevalence of mastitis was 61.18%, with the prevalence of subclinical cases (48.68%) far exceeding that of clinical cases (12.17%). At the quarter level, 30.75% of the teats were affected. The right rear quarter showed the highest incidence (34.21%), whereas the left front quarter was least affected (27.63%). Multivariate logistic regression revealed that breed (p=0.001), parity (p=0.001), milking hygiene (p=0.017), and teat end morphology (p=0.003) were significant predictors of mastitis. Staphylococcus aureus was isolated from 35.71% of mastitis-positive milk samples, including 37.39% from clinical samples and 35.06% from subclinical samples. Conclusion: This study revealed a high burden of both clinical and subclinical mastitis in dairy farms around Dessie Town, with S. aureus being a leading pathogen. The strong association between mastitis and risk factors such as hygiene and teat anatomy highlights the need for integrated control measures, farmer training, and routine screening to improve udder health and milk quality.