During the past five years, the number of broilers raised in the U.S. in no-antibiotics-ever programs has increased dramatically.
Grady Bishop, senior director, global market access, Elanco, told the audience at the Delmarva Poultry Industry Inc.’s National Meeting on Poultry Health, Processing and Live Production, Ocean City, Maryland, that the portion of U.S. broilers produced as no-antibiotics-ever birds has increased from just a few percent in 2012 to nearly 40 percent in 2017.
This rapid shift in how U.S. broilers are raised has come in response to purchase pledges by major quick-service restaurant chains like McDonald’s and Chick-fil-A and as major poultry integrators, Tyson and Perdue in particular, have made antibiotic usage in their flocks part of their retail brands’ marketing claims. This seismic shift in the marketplace, along with changes in the Veterinary Feed Directive, are also impacting how turkeys and table egg layers are being raised.
The antimicrobial resistance problem
Human and veterinary medicine are facing a long-term challenge: Fewer new antibiotics are being developed while at the same time the incidence of pathogenic bacteria that are resistant to one or more antibiotics is increasing. Governments around the globe are trying to find ways to maintain the efficacy of existing antibiotics while encouraging the development of new antibiotics.
The One Health approach that has been adopted to combat antimicrobial resistance looks at antibiotic use in humans and food animals. The marketplace now sees elimination of antibiotic use in poultry husbandry as a virtue, but will this change actually improve efficacy of antibiotics in human medicine?
Will removal of antibiotics reduce resistance?
There haven’t been a lot of studies looking specifically at the impact of no antibiotics ever growing programs for poultry on antimicrobial resistance of the microflora in the poultry house, according to Dr. Rolf Joerger, associate professor, department of animal and food sciences, University of Delaware. He did say that there has been some work done comparing antimicrobial resistance in bacteria on organic and conventional broiler farms. So far, he said that these studies have shown very little change in the level of antibiotic resistance in the pathogens.
“Right now, it is not completely clear if going to organic growing practices (which include no antibiotics ever) changes antimicrobial resistance in the short term, say within a few years.” Joerger explained that many of these studies just look at pathogens, not at all of the microbiota. He said that if you just look at pathogens, there aren’t that many of them, so your sample size is usually fairly small.
He said that if there will be a reduction in antimicrobial resistance in the poultry house that it may take years to develop, because the bacteria have been in the poultry house for a long time, particularly with built up litter systems. Joerger suggested that these bacteria may persist because they were adapted to that house environment.
Dr. Charles Hofacre, president, Southern Poultry Research Group, and professor emeritus, University of Georgia College of Veterinary Medicine, said that the National Antimicrobial Resistance Monitoring Study (NARMS) provided funding for research looking at antimicrobial resistance in the microflora of Salmonella and Campylobacter found in broiler houses. Hofacre and Dr. Randall Singer, professor of epidemiology, department of veterinary and biomedical sciences, University of Minnesota, conducted the research which continued after Hofacre’s retirement from the university.
In this field study, environmental samples were collected by wearing a sock over disposable boots and walking in the poultry house. Salmonella and Campylobacter were isolated and cultured from the samples and then were tested for antibiotic resistance according to the NARMS protocol. Birds raised in conventional and no antibiotics ever growing programs are included in the study, but the study commenced back when no antibiotics ever growing programs were a small niche part of the industry. Results for the study have not been published yet.
The problem of co-selection and co-resistance
Plasmids are small DNA circles outside the bacterial chromosome. Some bacteria can have plasmids that contain genes which provide resistance to more than one class of antibiotics or metals. Bacteria carrying plasmids like this are called co-resistant. Co-selection is the process where exposure to one antibiotic or metal selects for resistance to one gene in the plasmid and then also selects for all the other resistance genes that are in the plasmid.
Singer, speaking at the National Meeting on Poultry Health, Processing and Live Production, gave an example of how co-selection complicates efforts to halt the increase in antimicrobial resistance. He said that one plasmid pulled out of E. coli found in a cow conveyed resistance to a number of antibiotics as well as some metals like copper and zinc. Copper and zinc are sometimes used in no antibiotics ever growing programs to help regulate gut microflora, but if a plasmid containing genes for resistance to the metals and antibiotics were present on the farm, then we might not be improving resistance like we think we are.
Hofacre said that resistance genes to quaternary ammonia disinfectants has been found in plasmids containing antibiotic resistance genes, so how the farm or hatchery is cleaned could theoretically impact resistance to antibiotics.
Antibiotic resistance is a natural process
Just as the original antibiotics used in medicine were first found in nature, antibiotic resistance has evolved over millions of years in just about every environment on earth. We will never get to a zero level of antibiotic resistance. It evolved naturally long before humans harnessed antibiotics.
Joerger said the question is whether or not we can get back to what would be considered the natural or basal level of antimicrobial resistance in the bacteria in the bird’s environment. He said that no one really knows what the basal level of resistance really would be, but he said that it definitely wouldn’t be as high as what we see on poultry farms today.
Competitive exclusion and probiotics
Many successful no antibiotics ever husbandry programs for broilers, turkeys and laying hens utilize probiotics added to the feed to maintain healthy flocks with good performance. Hofacre said that a microorganism selected for inclusion as a probiotic because it helps keep Clostridia from colonizing the gut may not help prevent Salmonella colonization. In the future, Hofacre said that probiotic cultures containing more than one serovars of microorganism could be used to accomplish multiple objectives, like preventing colonization with Salmonella and improving bird health.
Probiotics could contribute to food safety by aiding the production of poultry products with reduced need for antibiotics, which could reduce selection pressure for antibiotic resistance in the poultry house. Probiotics could also help prevent colonization of digestive system with Salmonella and Campylobacter, which should means less of a pathogen load on ready-to-cook poultry products.
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This is the 12th article In WATT Global Media’s 100-year anniversary series, which looks at key drivers that will shape the future of the worldwide poultry industry
