EFFICACY OF FLORFENICOL FOR TREATMENT OF CLINICAL AND SUBCLINICAL BOVINE MASTITIS

Objective-To evaluate efficacy of florfenicol treatment for bovine mas titis caused by Streptococcus agalactiae, Staphylococcus aureus, nonag alactiae streptococci, coagulase-negative staphylococci, Escherichia c oli, Klebsiella sp, and others. Design-Double blind study with cases r andomly assigned to 1 of 2 treatment groups. Sample Population-851 cow s/10 commercial dairy farms. Procedures-Experimental (750 mg of florfe nicol) or control (200 mg of cloxacillin) treatment was administered b y intramammary infusion every 12 hours for 3 treatments to all cases. Treatments were randomly assigned, identified only by numerical labels . To retain blinding, the longer withdrawal time was adhered to for al l cases. Cases remained in the study only if there was no other treatm ent. Quarter samples were recultured 14, 21, and 28 days later. If all samples after day 1 were culture negative, the case was defined as cu red. If only 1 of the follow-up results was positive, the case was con sidered cured if the day-28 somatic cell count was < 300,000/ml. Failu re of treatment was defined as 2 or more culture-positive follow-up sa mples. Results-Florfenicol and cloxacillin did not differ significantl y in efficacy versus clinical (n = 85) or subclinical (n = 71) bovine mastitis, or for any etiologic agent (chi(2)). Overall cure rates for mastitis were: Str agalactiae, 5 of 8 (63%); Sta aureus, 5 of 54 (9%); Streptococcus sp, 16 of 35 (46%); Staphylococcus sp, 7 of 33 (21%); E coli, 5 of 11 (46%); Klebsiella sp, 3 of 6 (50%); others, 1 of 9 (11% ); and ail cases, 42 of 156 (27%). Conclusions-Florfenicol did not off er any advantage over cloxacillin in efficacy against bovine mastitis. Overall cure rates were low. As with most mastitis treatment regimens , poor efficacy may be partly attributable to the short duration of tr eatment.