USE OF CLINICAL-PARAMETERS FOR DIFFERENTIATION OF GRAM-POSITIVE AND GRAM-NEGATIVE MASTITIS IN DAIRY-COWS VACCINATED AGAINST LIPOPOLYSACCHARIDE CORE ANTIGENS

Objective-To determine whether clinical parameters could be used to di fferentiate clinical mastitis (CM) caused by gram-positive bacteria fr om CM caused by gram-negative bacteria in dairy cows vaccinated agains t lipopolysaccharide core antigens. Design-Case series. Animals-143 ep isodes of CM in 86 dairy cows in a single herd. Procedure-Cows were ex amined at onset of CM, and 24 clinical parameters including rectal tem perature, heart rate, rumen contraction rate, degree of dehydration, v arious udder and milk characteristics, lactation number, stage of lact ation, and season of year were recorded, Milk production and milk cons tituent concentrations before onset of CM were obtained from Dairy Her d Improvement Association records. Values for cows with gram-negative CM were compared with values for cows with gram-positive CM. Logistic regression was used to identify important predictors of gram-negative CM. Results-64 (45%) CM episodes were caused by gram-negative bacteria and 79 (55%) were caused by gram-positive bacteria. Rumen contraction rate was significantly lower and milk protein percentage before onset of CM was significantly higher in cows with gram-negative, rather tha n gram-positive, CM. Logistic regression indicated that CM was more li kely to have been caused by gram-negative bacteria if it developed dur ing the summer, milk was watery, or rumen contraction rate was low. Se nsitivity and specificity of the final regression model were 0.58 and 0.80, respectively. Predictive value of a positive result was 0.74 whe n proportion of CM episodes caused by gram-negative bacteria was assum ed to be 50%. Clinical implications-Results suggest that clinical obse rvations do not allow accurate prediction of CM pathogens and should n ot be the sole criteria for deciding whether cows with CM are treated with antibiotics.