The Impact of Restricting Antibiotic Use in Livestock: Using a 'One Health' Approach to Analyze Effects of the Veterinary Feed Directive
Dillon, Mary Ellen
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CitationDillon, Mary Ellen. 2020. The Impact of Restricting Antibiotic Use in Livestock: Using a 'One Health' Approach to Analyze Effects of the Veterinary Feed Directive. Master's thesis, Harvard Extension School.
AbstractOn January 1, 2017, the US FDA implemented a mandate that restricted the use of antibiotics in livestock production. GFI (Guide for Industry) #213 banned the use of antibiotics for growth promotion and required veterinarian permission, via the Veterinary Feed Directive (VFD), to deliver antibiotics through feed. This action was a response to concerns over the increasing incidence of resistance to antibiotics by bacteria. Its goal was to promote more judicious use of antibiotics in order to preserve their effectiveness.
My research took advantage of this nation-wide natural experiment to investigate how the VFD affected local (Ohio) livestock operations in terms of management practices and production levels. I also investigated the hypothesis that the anticipated national-level decreases in antibiotic consumption (ABC) by livestock may have been paralleled by a decrease in antibiotic resistance (ABR) in common zoonotic bacteria that inhabit both livestock and humans.
To explore the former, over fifty livestock producers (primarily cattle operations) and nine large animal veterinarians were interviewed. To test the conventional hypothesis that reduction of antibiotic use would negatively impact meat production, I examined ten-year production trends across all livestock sectors (swine, cattle, poultry), as compared to national trends for context. The interviews revealed that despite great initial concern, Ohio stakeholders reported adjusting to the new regulations with only minor difficulty. The most commonly reported changes due to the VFD were more veterinary-client interactions, more paperwork/record-keeping, and decreased use of fed antibiotics. No evidence of an adverse effect on meat production was found.
To explore national-level impact, I examined FDA Summary Reports to collect data on antibiotic consumption (ABC) by livestock, and then normalized consumption by animal species biomass. I collected NARMS (National Antimicrobial Resistance Monitoring System) data to examine resistance patterns in Salmonella and Campylobacter, the bacteria responsible for most US food-borne infections. Complete data for each animals species were available only for years 2016-2017, the years immediately prior to and post implementation of GFI #213.
My analysis revealed that Salmonella isolates showed significant changes in resistance to the antibiotic most used (and most reduced, 2016-17) in production across all species of food-producing animals. (Cattle/tetracycline, p = 0.007; swine/tetracycline, p = 0.023; turkey/penicillin, p = 0.009; chicken/tetracycline, p = 0.007). The latter, however, was opposite the direction predicted by natural selection. Further analysis suggested co-selection as an explanation. Campylobacter isolates generally appeared less responsive to the changes in livestock ABC, except for those isolated from chicken. Reduced chicken consumption of tetracycline was paralleled by significant decreases in tetracycline resistance by Campylobacter isolated from both chickens (p < 0.001) and humans (p=0.02). As chicken meat is the source of most US Campylobacter infections, this may represent preliminary evidence of early human health benefits of GFI #213.
In conclusion, veterinarians and livestock producers appear to have successfully adapted to GFI #213. The mandate appears to be working, both in terms of decreasing the consumption of antibiotics by livestock and in reducing the occurrence of ABR in bacteria that inhabit both livestock and humans, affirming the “One Health’ approach.
Citable link to this pagehttps://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37365628
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