Evaluation of 9 Treatments, Including No Treatment, for Efficacy Against 21 Different Bovine Mastitis Pathogens

Abstract

Milk culture results from approximately 540,000 cows housed in approximately 3,500 dairy herds located in New York and northern Pennsylvania were retrospectively reviewed. 9563 cases included in analysis were cultured in consecutive months, had permanent cow identification, records of clinical mastitis signs (if present), records of whether mastitis was treated with an antibiotic, unknown or antibiotic combination, or no treatment at all. Overall bacteriological cure rate was 68.0% (6503/9563); subclinical cases, 67.9% cure rate (6311/9290), did not differ from clinical cases, 70.3% cure rate (192/273). Treated cases had a higher cure rate (75.3%) than untreated cases (64.8%). Antibiotic treatments that significantly differed from the overall cure rate of 68.0% were: amoxicillin 82.4%; unknown/combined treatments 76.3%; erythromycin 76.2%; cloxacillin 73.6%; pirlimycin 43.8%. Cephapirin, hetacillin, and penicillin did not differ from the mean cure rate or from the untreated cure rate. Agents for which some antibiotics were associated with increased cure rates, compared with no treatment, included Streptococcus agalactiae, streptococci other than Strep ag, and Corynebacterium bovis. The antibiotic most commonly associated with higher cure rates was amoxicillin. Most mastitis agents showed no difference in bacteriologic cure rates in association with any treatment, including no treatment.