Evaluation of antibiotics for treatment of cattle infected with Leptospiraborgpetersenii serovar hardjo

Objective To evaluate antibiotics for treatment of cattle with leptospirosi s caused by Leptospira borg-petersenii serovar hardjo. Design-Randomized controlled trial. Animals-42 healthy mixed-breed cattle. Procedure Cattle were inoculated via conjunctival instillation with L borgp etersenii serovar hardjo. After infection and urinary shedding of L borgpet ersenii were confirmed, cattle were treated with various antibiotics. To de termine effectiveness of antibiotic treatment, urinary shedding of L borgpe tersenii was monitored for 4 to 6 weeks after administration of antibiotics , using darkfield microscopic examination, microbial culture, immunofluores cence testing, and a polymerase chain reaction assay. Results-All inoculated cattle developed leptospirosis and shed leptospires in their urine. The following antibiotic treatments resulted in elimination of urinary shedding of leptospires: a single injection of oxytetracycline (20 mg/kg [9 mg/lb] of body weight, IM), tilmicosin (10 mg/kg [4.5 mg/lb], SC), or a combination product that contained dihydrostreptomycin-penicillin G (25 mg/kg [11.4 mg/lb], IM) or multiple injections of ceftiofur sodium ( 2.2 or 5 mg/kg [1 or 2.3 mg/lb], IM, once daily for 5 days, or 20 mg/kg, IM , once daily for 3 days). Conclusions and Clinical Relevance-Successful resolution of leptospirosis i n cattle by administration of dihydrostreptomycin-penicillin G confirms res ults obtained by other investigators. Three other antibiotics (oxytetracycl ine, tilmicosin, and ceftiofur) also were effective for resolving leptospir osis and may be useful substitutes for dihydrostreptomycin, an antibiotic t hat is no longer available for use in food-producing animals in the United States. Cost, safety, and withdrawal times of these various treatment optio ns need to be considered.