Comparison of antibiotic administration in conjunction with supportive measures versus supportive measures alone for treatment of dairy cows with clinical mastitis.

OBJECTIVE: To determine whether antibiotic and supportive treatment would improve outcome for dairy cows with naturally developing clinical mastitis, compared with supportive treatment alone.
DESIGN: Randomized controlled trial. ANIMALS: 124 cows in one herd with 172 episodes of clinical mastitis. PROCEDURE: Cows were examined at the onset of clinical mastitis, assigned a severity score, and randomly assigned to receive antibiotic (intramammary administration of cephapirin, i.v. administration of oxytetracycline, or both) and supportive treatment (administration of oxytocin, stripping of affected glands, and, in severely affected cows, administration of flunixin meglumine or fluids) or supportive treatment alone. Treatment was continued until 24 hours after signs of clinical mastitis resolved (clinical cure). Milk samples from affected glands were submitted for bacterial culture before initial treatment and every 2 weeks thereafter until the causative organism was no longer isolated (bacteriologic cure).
RESULTS: When mastitis was caused by Streptococcus spp or coliform bacteria, clinical cure rate by the tenth milking was significantly higher if antibiotics were used. Bacteriologic cure rate at 14 days was significantly higher when antibiotics were used, particularly if mastitis was caused by Streptococcus spp. Cows receiving antibiotics developed fewer subsequent episodes of clinical mastitis during the 60 days after the initial episode of mastitis and had less severe clinical disease than cows that did not. CLINICAL IMPLICATIONS: Results suggest that, in herds in which mastitis is often caused by environmental bacteria, antibiotic and supportive treatment may result in a better outcome for cows with clinical mastitis than supportive treatment alone.