title: Ability of hematologic and serum biochemical variables to differentiate gram-negative and gram-positive mastitis in dairy cows.
abstract: Medical records of 142 dairy cows with clinical mastitis were examined to determine whether hematologic or serum biochemical results could be used to distinguish between mastitis episodes caused by gram-negative bacteria (n = 78) from those caused by gram-positive bacteria (n = 64). Signalment, historic information, hematologic and serum biochemical results, milk culture results, and outcome (discharged from hospital or died) were obtained from the medical records. Cows with gram-negative mastitis had significantly (P < .01) lower blood leukocyte, segmented neutrophil, monocyte, and lymphocyte counts and had higher blood hemoglobin concentrations and hematocrits than did cows with gram-positive mastitis. Serum urea nitrogen was the only serum biochemical result associated with pathogen type, and it was higher in cows with gram-negative mastitis than in those with gram-positive mastitis. Mortality rate (25% overall) did not differ between groups. Logistic regression indicated that routine hematologic analysis (segmented neutrophil count, monocyte count, and hemoglobin concentration) was an accurate predictor of gram-negative mastitis, with a sensitivity of .93, a specificity of .89, and an overall accuracy of 91%. The values for sensitivity and specificity were higher than those previously reported for clinical tests differentiating mastitis episodes caused by gram-negative bacteria from those caused by gram-positive bacteria. Our results indicate that routine hematologic analysis is useful for predicting pathogen type in dairy cows with clinical mastitis, thereby facilitating treatment decisions.
authors.affiliation: Department of Veterinary Clinical Medicine, University of Illinois, Urbana 61802, USA. gw-smith@uiuc.edu
authors.forename: G W
authors.initials: GW
authors.lastname: Smith
authors.forename: P D
authors.initials: PD
authors.lastname: Constable
authors.forename: D E
authors.initials: DE
authors.lastname: Morin
mesh_terms: D000818:Animals; D001774:Blood Chemical Analysis / Q000592:standards / Q000662:veterinary; D001806:Blood Urea Nitrogen; D002417:Cattle; D003612:Dairying; D005260:Female; D006090:Gram-Negative Bacteria / Q000302:isolation & purification*; D006094:Gram-Positive Bacteria / Q000302:isolation & purification*; D006403:Hematologic Tests / Q000592:standards / Q000662:veterinary; D016015:Logistic Models; D008414:Mastitis, Bovine / Q000097:blood / Q000175:diagnosis* / Q000382:microbiology; D008892:Milk / Q000382:microbiology; D011237:Predictive Value of Tests; D011996:Records / Q000662:veterinary; D012189:Retrospective Studies; D012680:Sensitivity and Specificity