Effect of penicillin or penicillin and dexamethasone in cattle with infectious bovine keratoconjunctivitis.

To evaluate the efficacy of penicillin or penicillin and dexamethasone for treatment of infectious bovine keratoconjunctivitis, 6- to 8-month-old beef heifers with clinical signs of infectious bovine keratoconjunctivitis were randomly assigned to 1 of 3 treatment groups: penicillin only, penicillin and dexamethasone, or control. Cattle assigned to the penicillin group (n = 18) were treated with 3 daily subconjunctival injections of procaine penicillin G. Cattle assigned to the penicillin/dexamethasone group (n = 13) were treated with 3 daily subconjunctival injections of procaine penicillin G and dexamethasone sodium phosphate. Control cattle (n = 14) were not treated. Healing times and frequency of recurrence for corneal ulcers; severity, diameter, and surface area measurements of corneal ulcers; and clinical scores did not differ among the 3 groups. Frequency of Moraxella bovis isolation from specimens of ocular secretions from ulcerated and non-ulcerated eyes was similar in all groups. Minimum inhibitory concentration of penicillin G for 95 of the 102 tested M bovis isolates was 0.3 U/ml, and for 7 others was 0.03 U/ml. When first and last specimens from 42 of 45 calves with isolation of M bovis on serial microbial cultures were compared, the susceptibility of each last isolate was similar to that of the corresponding first isolate.