0156 Effect of the selective treatment of gram-positive clinical mastitis cases versus blanket therapy

This study objective was to compare antibiotic use, clinical and bacteriological outcomes for selective treatment of only Gram-positive clinical cases versus blanket therapy. Cows with mild or moderate clinical mastitis (CM) from a California Central Valley dairy herd were assigned to either a) a positive-control treatment group (PC) or b) a laboratory-culture-based treatment group (CB). Quarter cases assigned to PC received immediate intramammary (IMM) treatment with ceftiofur (Spectramast LC; Zoetis Inc., New York, NY) and repeated once a day for a total of 3 d. Quarters assigned to CB underwent culture over a 24 h period at DairyExperts Laboratory (DairyExperts Inc., Tulare, CA). Only quarters showing Gram-positive growth were treated the next day with the same therapy as cases assigned to PC. Mixed Models were used with cow included as a random effect. A total of 473 quarter cases of clinical mastitis from 425 cows were enrolled into the study. Results are summarized on Table 1. The selective treatment of only CM cases from which Gram-positive bacteria was isolated resulted in about half reduction both in the number of cases treated and in the number of IMM tubes used. Furthermore, the withholding of antibiotic treatment did not have any deleterious effect on time for milk to return visibly normal, bacteriological cure, new infection risk, CM recurrence or removal from the herd.