Intramuscular administration of ceftiofur sodium versus intramammary infusion of penicillin/novobiocin for treatment of Streptococcus agalactiae mastitis in dairy cows

Abstract

Objective: To determine the efficacy of intramuscular administration of ceftiofur sodium as treatment for intramammary infections attributable to Streptococcus agalactiae, compared with that for a standard treatment of intramammary infusion of penicillin/novobiocin. Design: Prospective, randomized, controlled trial. Animals: 72 lactating Holstein cows with intramammary infections caused by S agalactiae from 5 commercial dairies in Michigan. Procedure: In 36 of 72 infected cows, ceftiofur was administered (2.2 mg/kg of body weight, IM, q 24 h) for 5 days; 150 mg of novobiocin and 100,000 U of procaine penicillin C was infused daily into each mammary gland of the other 36 cows for 2 days. Milk samples were collected aseptically at approximately 4 and 8 weeks after initial treatment. If cows were determined to be infected at 4 weeks after initial treatment, the treatment was repeated. Results: The cure rate at 4 weeks (91.7%) and at 8 weeks (96.8%) after initial treatment for the penicillin/novobiocin-treated cows was significantly (P < 0.0001) higher, compared with that of the ceftiofur-treated cows (2.8 and 9.1%, respectively). Somatic cell counts were significantly (P < 0.0001) lower in the penicillin/novobiocin-treated group after treatment. Clinical Implications: Intramuscular administration of ceftiofur is not efficacious as a treatment to eliminate intramammary infections caused by S agalactiae and should not be used to reduce the prevalence of this organism in dairy herds.