Data on antibiotic use won’t stop resistance, says expert

The U.S. has introduced regulations requiring livestock producers to work with veterinarians in administering antibiotics

SAN DIEGO, Calif. — New rules overseeing the use of antibiotics in livestock production in the United States should provide better data about drug use, but they will not reduce antimicrobial resistance.


“If antibiotic resistance is the issue, that is what we need to be monitoring and we need to be monitoring it on a local level,” said Dan Thomson, professor of clinical studies at Kansas State University.


Thomson, who outlined government requirements for the Veterinary Feed Directive at the Jan. 26-29 National Cattlemen’s Beef Association convention in San Diego, said the new system will show five years from now that antibiotic use is down, but resistance will persist. 


The U.S. Food and Drug Administration has said it wants to collect data on antibiotic use in food producing animals and is collaborating with the U.S. Department of Agriculture and the Centers for Disease Control and Prevention to develop a plan to build a database to evaluate the changing trends of antimicrobial resistance. 


“When combined with new on-farm data, this will provide a more comprehensive and science-based picture of antibiotic drug use and resistance in animal agriculture,” the FDA said in statement published late last year.


Many in the livestock industry argue that resistance is not entirely the fault of administering antibiotics to animals. 


“The most common cause of antibiotic resistance in human beings is the over-prescribing of antibiotics by medical doctors,” Thomson said. 


“When we are going to have antimicrobial resistance problems from beef into the human population, it is going to come from antibiotic resistance in food-borne pathogens,” including E. coli 0157:H7, salmonella and campylobacter.


However, the risk of contracting these illnesses is extremely low because of food safety programs. 


A greater threat occurs in developing countries, where there are no regulations or prescriptions necessary to buy antibiotics. Thomson said no one monitors use in Africa or India, so resistance transfer is exacerbated.


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He said if an antibiotic resistant bacteria does develop, there’s a high probability that it will occur in the slums of developing countries where there is little oversight on antibiotic use. People may also have a greater chance of picking up disease from animals such as goats, pigs or chickens because they tend to live together.


Thomson also said the transfer of antimicrobial resistance between animals and humans is more likely to occur among pet owners because less attention is paid to the kind of drugs given to small animals. 


Nevertheless, new regulations on livestock use are in place and will change common past practices. 


The rules require livestock producers to have a veterinary-client relationship to use antibiotics on the farm. Veterinarians are expected to work with producers and know the farm and its herd health program.


No antibiotics in feed will be allowed without a prescription. The producer has to agree to comply with the prescription as written by the veterinarian.


Growth promoting claims on labels for in-feed antibiotics are no longer allowed. These products may be used only by prescription for treatment, control or prevention of disease.


Thomson said this does not significantly change common practices, other than the requirement for a prescription before buying antibiotics. 


Ionophores and coccidiostats do not require prescriptions.


Three copies of the prescription records are required and must be kept for two years. Veterinarians, producer and supply stores each keep a copy. 


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The veterinarian must set an expiry date of no longer than six months on each prescription.


Thomson is concerned that some commonly used products could be taken off the market as these rules are enforced.


Tylosin, a broad-spectrum antibiotic added to animal feed, is one drug that may be affected. It has been sold as a growth promoter but can treat a variety of infections. 


“If we lose antibiotics or other tools, we will never get them back. We learned that with Zilmax,” he said, referring to a beta agonist in feed that was linked to lameness in cattle. 


Europe, which already has similar policies, found an increase in the use of more powerful prescription products when lower class products were removed. 


Some of these changes are driven by consumer demands for hormone and antibiotic free meat, but most consumers probably don’t know anything about these products. 


Thomson said the average consumer wants assurances that the agriculture industry is constantly improving while still offering a reasonably priced product. 


For example, there are three nanograms of estrogen in an implanted steer, while a non-implant animal has two nanograms in its system. 


A nanogram per kilogram is the equivalent of a blade of grass in a football field. 


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Pregnant women have about 19,600 nanograms of estrogen, while an adult male has 135,000 nanograms and prepubescent children have 41,000 nanograms.