AMES, Iowa — Veterinarians are obligated to treat sick animals, and that may require antibiotics.
“There is a growing sense that these uses are an unacceptable risk, and this is a strong motivator for the raised-without-antibiotics in consumer choices,” said veterinarian Paul Morley of West Texas A & M University.
The public may have strong ideas about antibiotic use and the possibility of residues in animals harming people and the environment, he said at the National Institute of Animal Agriculture antibiotic symposium held in Ames, Iowa.
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“If we really believe use is causing resistance and it is affecting the health of people, it is an important question to try and understand where those ties are strong,” he said.
Systems are in place to ensure residues do not enter the food system, but for the most part the public does not know this.
Cattle tend to receive tetracycline and macrolides, while people are prescribed cephalosporins. Treatment failures have occurred because of resistance, but scientists such as Morley want to learn more about cause and effect.
“Just because we find resistance appearing in animals doesn’t mean it is associated with treatment of the animals,” he said.
Researchers can obtain more detailed data at the genetic level about microbes and their behaviour to dissect what leads to resistance, but the conclusions may often lead to more questions.
Morley was involved in a feedlot project to see if animals raised without antibiotics showed a difference in the prevalence of antimicrobial resistant bacteria compared to those under conventional care. No resistance differences were found.
“We have tried really hard to try and find those associations with use practices in cattle and resistance, and only the acute things that we are measuring seem like that is having an impact and they do not seem to persist,” he said.
Another study collected ground beef samples in raised-without-antibiotics and conventional programs, and no difference was found in the presence of resistant bacteria.
He theorizes that some resistance may decline during the feeding period in a small percentage of animals tested.
“Almost all of the classes of antibiotics and almost all the types of samples that we had, there was a decrease over time in resistance, not an increase,” he said.
More research is needed.
“The truth about antimicrobial resistance is that it is extremely complicated, and society wants simple,” he said.
“We need to use antibiotics less frequently, and we have to realize the public is not necessarily interested in the science answers.”
Placing blame is also misdirected.
It is not the producer’s fault if an antibiotic resistant pathogen is found.
“Producers are trying to use evidence as the best way to manage the cattle, and we are saying in a non-evidence based manner, don’t do that,” he said.
“There is a problem with the idea if we find a resistant organism in an animal that the anthropogenic hypothesis fits that we caused it to be resistant due to use of antimicrobials in that animal,” he said.
“It is a disconnect between the question of how did the food-borne pathogen get there to how did that pathogen become resistant?”
