Ability of hematologic and serum biochemical variables to differentiate gram-negative and gram-positive mastitis in dairy cows.
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.
Smith
G W
GW
Department of Veterinary Clinical Medicine, University of Illinois, Urbana 61802, USA. gw-smith@uiuc.edu
Constable
P D
PD
Morin
D E
DE
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