Bacteremia associated with naturally occurring acute coliform mastitis in dairy cows

Objective-To determine the incidence of bacteremia in dairy cows with natur ally occurring acute coliform mastitis (ACM) with a wide range of disease s everity. Design-Cohort study. Animals-144 dairy cows with ACM from 6 herds. Procedure Cows were examined at time of identification of ACM (time 0) and classified as having mild, moderate, or severe mastitis on the basis of rec tal temperature, hydration status, rumen contraction rate, and attitude. Co ws were reexamined at 24 or 48 hours. Bacteriologic culturing of milk and b lood (30 ml), CBC, and serum biochemical analysis were performed at each ti me point. Appropriate samples were obtained at a single point from herdmate s without mastitis (controls) that were closely matched for lactation numbe r and days since parturition. Blood culture results were compared among sev erity groups and controls by use of chi (2) tests, as was outcome of an ACM episode for cows grouped by blood bacterial isolates. Results-Bacteria were isolated from 52 blood samples from 46 of 144 (32%) c ows with ACM, which was significantly more than control cows (11/156; 7.1%) . Group-1 isolates (Escherichia coli, Pasteurella multocida, Mannheimia hae molytica, Klebsiella pneumoniae, Enterobacter agglomerans, and Salmonella e nterica serotype Typhimurium) were identified in 20 of 144 (14%) cows with ACM and 0 of 156 control cows. Group-1 isolates were identified in 4.3, 9.1 , and 42% of cows classified as having mild, moderate, and severe ACM, resp ectively, Escherichia coli and K pneumoniae milk and blood isolates obtaine d from the same cow were of the same genotype. Bacillus spp were identified in 21 of 144 (15%) cows with ACM, which was significantly more than contro l cows (3/156; 1.9%). Thirty-five percent of cows with a group-1 isolate di ed during the mastitis episode. Conclusions and Clinical Relevance-Results suggest that bacteremia develops in a substantial proportion of cows with ACM. Classification of severity o f disease is important for establishment of effective treatment protocols; parenteral antimicrobial treatment may be indicated in cows with ACM.