Editor’s note: last in a series.
Over the years several methods have been tried, with varying results, to prevent and control leptospirosis caused by serovar Hardjo-bovis in cattle. Renewed efforts are being made to identify serovars and manage the disease.
One option many veterinarians have used to clear lepto infections has been the use of long-acting tetracycline. Leptospira organisms are bacteria, so antibiotic therapy intuitively makes sense. “If we take the organisms out of the cow, they’re susceptible to virtually every antibiotic made,” says Carole Bolin, DVM, PhD, Diagnostic Center for Population and Animal Health, Michigan State University. “However, the issue in the cow is getting the drug levels high enough at the site of infection for long enough periods of time to solve the problem.”
Bolin notes that in other countries, long-acting amoxicillin has been used successfully, but that option is not available in the United States. “So we look at multiple injections of tetracycline to maintain blood levels for a significant period of time, which becomes a real management problem.” She adds that another problem is that a single, efficacious injection would be at the dose for respiratory disease (9 mg/lb) which is a large volume of drug and requires administration at multiple sites.
Bradley Mills, DVM, Rocky Creek Veterinary Services, Olin, N.C., started using antibiotics before an efficacious serovar Hardjo vaccine was available. “We gave oxytetracyline at dry-off, which is an extralabel use, but we saw a clinical response in that we cut out a lot of abortions and premature calving. We now vaccinate whole herds of cattle because we have to both clear infections and stop transmission.”
Antibiotic treatment will not eradicate the disease, however. Mark Hardesty, DVM, Maria Stein Animal Clinic, Inc., Maria Stein, Ohio, at one time thought that was possible because of the excellent results he achieved with long-acting tetracycline given at dry-off. Within six months there was a positive effect on reproductive performance. “We thought we’d conquered that mountain,” he says. “But a year and a half later we were back at the bottom of the mountain again and had to re-institute antibiotic therapy.”
Hardesty says he’s comfortable with the extra-label use of the long-acting tetracycline because he’s fulfilled the requirements of the Animal Medicinal Drug Use Clarification Act (AMDUCA). “Bovine practitioners live in an exciting time where prudent, diagnosis-based drug use will supplant untargeted treatments. We’ve done the diagnostics and have published data from the Journal of Dairy Science that says it’s effective. Plus, there are no other tools effective for clearing the infection.”
Once you’ve aggressively attacked the Hardjo-bovis problem on an operation, every animal coming to the farm is a risk unless its status is known.