Efficacy of parenteral administration of three antimicrobial agents in treatment of clinical mastitis in lactating cows: 487 cases (1989-1995)

Abstract

Objective To evaluate the efficacy of parenteral administration of procaine penicillin G, spiramycin, or enrofloxacin in the treatment of clinical mastitis in lactating cows. Design Noncontrolled, clinical retrospective study. Animals 487 cows with mastitis involving 543 quarters. Procedure Clinical signs, histories, and results of bacteriologic examination, somatic cell count, and N-acetyl-β-d-glucosaminidase activity of milk samples taken before and 3 to 4 weeks after treatment were retrieved from hospital records. Cows treated parenterally with procaine penicillin G, spiramycin, or enrofloxacin for 3 to 5 days were included. Supportive treatment alone was given to 35 cows infected with Escherichia coli. Factors possibly affecting outcome were analyzed, using ANOVA, correlation analyses, and the Mann-Whitney test. χ2 Test was used to compare bacteriologic cure rates. Results Bacteriologic cure rates for mastitis caused by Staphylococcus aureus, coagulase-negative staphylococci, and streptococci were 34, 76, and 65%, respectively. Cure rates in cows in their first lactation and infected with S aureus and coagulase-negative staphylococci were significantly higher than those for older cows. In cows with mastitis caused by E coli, the cure rate was 74% for those treated with penicillin G and 71% for those not treated with antimicrobials. High N-acetyl-β-d-glucosaminidase activity in milk samples obtained at initial examination indicated a poor outcome in S aureus and streptococcal mastitis. Cows infected in the early lactation period had more severe inflammatory responses and clinical signs if infected with coagulase-negative staphylococci and coliforms. Clinical Implications 3 to 5 days of treatment with parenterally administered penicillin G for clinical mastitis caused by penicillin-susceptible S aureus strains is efficacious in young cows. Parenteral administration of spiramycin or enrofloxacin does not give satisfactory results in mastitis caused by penicillin-resistant S aureus. Use of antimicrobials in the treatment of mastitis caused by coliform bacteria is questionable. (J Am Vet Med Assoc 1998; 212:407-412)