Prevalence of subclinical mastitis, associated risk factors and antimicrobial susceptibility of the pathogens isolated from milk samples of dairy cows in Northwest Ethiopia.

Subclinical mastitis (SCM) is a problem of dairy cattle worldwide that affects the income of dairy farmers and besides a health risk to humans. A cross-sectional study was carried out to estimate prevalence, identify risk factors of SCM and antimicrobial susceptibility test of bacteria isolated from SCM quarters. California Mastitis Test (CMT) positive milk samples were cultured and bacteria isolated. The isolated bacteria were checked for their antimicrobial susceptibility using Kirby-Bauer disk diffusion method. The study findings showed that 32.7% of the quarters and 60.1% of the cows were CMT positive. The isolated bacteria were 29.5% Staphylococcus aureus (S. aureus) and 9.3% Streptococcus agalactiae (Str. agalactae). In the risk factors study, cows from farms of poor hygiene, increased age and stage of lactation had higher odds of SCM. Of the isolated bacterial species, 75.7% and 71.4% of S. aureus isolates were resistant to the effects of penicillin and ampicillin, respectively. Streptococcus agalactiae were resistant to the effects of oxytetracycline (76.9%), streptomycin (61.5%) and cloxacillin (53.8%). Whereas the majority of S. aureus (98.6%) and Str. agalactiae (88.5%) were susceptible to the effects of gentamycin and Clindamycin respectively. In conclusion, SCM had high level of prevalence and associated risk factors with pathogens that were resistant to commonly used antimicrobials. Implementing strict preventive measures and limiting spread of pathogens is a preferred approach rather than treatment with antibiotics to control mastitis in the study area.