A cross-Sectional Study of Bovine Mastitis In and Around Bahir Dar and Antibiotic Resistance Patterns of Major Pathogens

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Addis Ababauniversity


Three hundred fifty one (195 local zebu and 156 Holstein x Local Zebu) lactating cows of smallholder private farms in Bahir Dar milk shed were examined from September, 2003 to March, 2004 to determine mastitis prevalence, isolate pathogens involved, evaluate the antibiotic susceptibility profiles and to evaluate somatic cell count in identifying intramammary infections. Clinical prevalence was determined through examination of abnormalities of milk, udder or cow. California mastitis test (CMT) and culture were used for subclinical mastitis determination. Agar disc diffusion was used for antibiotic susceptibility test. Somatic cell count was conducted following standard procedures described in International Dairy Federation for enumeration of cells with direct Microscopic method. Clinical prevalence at cow level was 3.9% in crossbreds and none in local zebu breeds. Subclinical mastitis at cow level based on CMT was high (34.4%) in crossbreds compared to indigenous zebu (17.9%) (p < 0.05). Quarter subclinical prevalence based on CMT was 17.90% and 4.95% for crossbreds and local zebu, respectively. Among potential risk factors considered, stage of lactation, parity and breed were found to affect the occurrence of mastitis significantly (p < 0.05). The pathogens isolated from mastitic milk were coagulase negative staphylococci (CNS), S. aureus, Str. agalactiae, Str. dysgalactiae, Str. uberis, Micrococcus species, C. bovis, A. pyogens, B. cereus, and S. intermedius. Among these, the most frequent isolates were CNS (49.6% of the total isolates), S. aureus (17.9%), Str. agalactiae (8.2%) and Str. dysgalactiae (6.7%). Seven antibiotics including sulfisoxazole, tetracycline, erythromycin, oxacillin, chloramphenicol, clindamycin, and streptomycin were tested on 81 isolates. Except for streptomycin, all isolates were sensitive to all antibiotics. All isolates were most sensitive to sulfisoxazole. Staphylococcus aureus was susceptible to all drugs except streptomycin. Staphylococcus aureus was 91.7% susceptible to oxacillin, however, CNS were less susceptible (68.2%) in vitro. To evaluate somatic cell count (SCC) in identifying intramamary infection for crossbreds, 10 cutoff points between 100000 cells/ ml and 300000 cells/ml were evaluated for their sensitivity and specificity in comparison with cultural results. Similarly, cutoff points between 80000 cell/ml and 250000 cell/ml were taken for local zebu breeds. The sensitivity for viii crossbreds range from 79.16 % (at 300000 cells/ml cutoff point) to 95.80 % (at 100000 cells/ ml) and similarly specificity from 80.28% to 45.52%. For local zebu breeds in the same order, sensitivity range from 58.82% to 88.23% and specificity from 45.82% to 85.15%. To establish threshold level this study was a first attempt in Ethiopia and to use SCC as a diagnostic tool on a national scale further study need to be conducted with improved cultural technique and automatic cell counters. Cross breed cows had high SCC compared to local zebu cows. The SCC was significantly (p<0.05) affected by infection status, breed and late lactation stage. Keywords: clinical / subclinical mastitis/ prevalence/ bacterial isolate/ antibiotic susceptibility / Somatic Cell Count / threshold / crossbred / zebu



clinica, subclinical mastitis, prevalence, bacterial isolate, antibioticsusceptibility, Somatic Cell Count, threshold, crossbred, zebu