Editor’s note: Last month, Dairy Herd Management carried a special 12-page insert on the judicious use of antibiotics in food-animal species. 

Recently, I served on a scholarship selection committee for veterinary students interested in bovine practice. The selection process involved many criteria, but one was a written answer to the essay question, “Antimicrobial resistance: Is the veterinarian part of the problem or part of the solution?” 

Many of the students had excellent, thoughtful answers, but reading their answers certainly triggered some thoughts and assessment of my own — about both my clients and my own practice.

Resistance to antibiotics is a phenomenon that has been observed in bacterial populations ever since antibiotics were discovered. Treating a bacterial infection with an antibiotic will kill all of the susceptible bacteria. However, if a few bacteria have genetic resistance to that antibiotic, they will survive. These survivors can then pass this genetic resistance on to other bacteria.

Over time, antibiotics that were once extremely useful in killing bacteria have become ineffective. This phenomenon is well known, undoubtedly, to many bovine practitioners, where the pattern of drug sensitivity to mastitis, calf diarrhea, and pneumonia has certainly changed during the past few years.

The risk
Antibiotic resistance among bacteria in food-producing animals may affect our pocketbooks, due to increased animal losses and extra costs to fight disease. However, that’s just the starting point.

These resistant bacteria make it more difficult to effectively treat sick people when they get similar bacterial diseases. Two diseases of concern are salmonellosis and E. coli.

People usually get these diseases from eating contaminated meat that has been prepared improperly. If the bacteria have developed resistance to antibiotics from the use of antibiotics in cattle, pigs, or chickens, then treatment by that same antibiotic in the sick person will be ineffective. I have tended to regard this as more of a theoretical problem than a practical one.

A research paper in The New England Journal of Medicine demonstrates that it is more than just a theoretical problem. In a study involving human cases of salmonella in Taiwan, resistance to the class of antibiotics known as flouroquinolones was closely related to the emergence of resistant strains of salmonella in swine. The salmonella that caused the disease in people — which they probably got by eating improperly cooked pork — had developed some resistance to flouroquinolones. That resistance more than likely was developed from pigs in Taiwan being fed subtherapeutic levels of enrofloxacillin, a type of flouroquinolone.

Proper use
Typically, the problems with resistant bacteria in humans involve staphylococcus infections acquired in hospitals, and probably result from the misuse of antibiotics in the human population and poor sanitation.  However, the Taiwanese cases referenced in The New England Journal of Medicine show a possible connection to antibiotic use in food animals.

The American Veterinary Medical Association and American Association of Bovine Practitioners have developed guidelines for the prudent use of antibiotics in cattle. They include:

  • Good management, including sanitation and vaccination protocols, should be used to minimize the necessity of antibiotic usage.
  • When used, antibiotics should be selected and targeted based on the probable sensitivity of the disease-causing organism. The most specific antibiotic likely to be effective should be chosen.
  • Antibiotic selection, whenever possible, should be based on specific culture and sensitivity data for the affected farm.
  • Whenever possible, an antibiotic labeled for the specific problem should be used. When not possible, an extra-label drug with the narrowest possible spectrum of activity, should be used and only used within the constraints of a valid veterinarian-client-patient relationship.
  • Farm personnel should be trained to properly administer antibiotics.

Judicious and careful use of our power to select and administer antibiotics is needed. Someday, in the hospital, we may be thankful.

Brian Gerloff  is a veterinarian and operates Seneca Bovine Service in Marengo, Ill.