Efficacy of intramuscular oxytetracycline as a dry cow treatment for Staphylococcus aureus mastitis.

To determine the efficacy of intramuscular oxytetracycline as a supplemental dry cow treatment for Staphylococcus aureus mastitis, 37 Holstein cows were randomly assigned to two treatment groups: intracisternal infusion with a commercial preparation of cephapirin benzathine at drying off (20 cows) and infusion with cephapirin benzathine at drying off and intramuscular oxytetracycline at 11 mg/kg once daily on d 7, 8, 9, and 10 after drying off (17 cows). Milk samples collected 7, 14, 30, and 60 d after calving were plated for bacterial isolation within 24 h after collection and after 24 to 72 h of storage at -20 degrees C. Quarters were defined as infected if S. aureus was isolated from the fresh and frozen cultures from any one sample collected before drying off. An infected quarter was defined as cured if S. aureus was not isolated from the fresh or frozen culture from milk samples obtained following calving. The rate of cure by 30 d after calving for systemic oxytetracycline (in combination with cephapirin treatment) was 29.4% for infected quarters and 29.4% for infected cows, compared with 27.5 and 25.0%, respectively, for the cephapirin treatment only. Results including the culture at 60 d after calving were 21.2 and 22.5%, respectively, for combination therapy and cephapirin therapy only. Systemic oxytetracycline, in combination with intramammary dry cow treatment, did not improve the rate of cure for S. aureus mastitis.