Antibiotic resistance key to understanding efforts to curtail antibiotics in poultry
The reduction and removal of antibiotics from poultry feeds is now a common theme for producers. This is due to rising levels of antimicrobial resistance and not because of the antibiotics themselves. Ensuring that antibiotics are only used for the treatment of disease in birds will relieve pressure on the industry, but at what price to poultry performance?
Antimicrobial resistance, not antibiotics themselves, motivate the drive for antibiotic reduction.
Consumer demand, regulation and a lack of new antimicrobial molecules all contribute to the current, long-term trend to reduce antibiotics in modern poultry systems. While the need for consumer education around food production remains an open question, it is the ability of bacteria to become resistant to one or more antibiotics –rendering those drugs ineffective– and the profound implications for both human and animal health that account for the need to reduce antibiotics.
Resistance in the crosshairs
According to the World Health Organization (2011), "any kind of antibiotic use in people, animals or plants can promote the development and spread of antibiotic resistance." The identification of antibiotic use in farm animals as a risk factor in the development of antibiotic resistant bacteria explains why antimicrobial resistance has continued to garner greater attention from health authorities and regulators worldwide, particularly for antibiotics deemed important to human medicine.
This concern is separate from antibiotic residues potentially finding their way into meat and eggs: withdrawal periods and monitoring have already been established to ensure that antibiotics do not enter the food supply.
Figure 1. Prescribed antimicrobial agents for human and all animal species
Protecting valuable health tools
The need to preserve antimicrobial substances stems from the fact that they represent, to some extent, a limited resource. The most recent class of antibiotics was discovered in 1987. The research and development pipeline for new antimicrobials has remained largely unfilled. According to the Organisation for Economic Co-operation and Development (OECD, 2016), only five new classes of antibiotics have been brought to market since 2000.
The development of bacterial resistance to an antibiotic in the years following its introduction, estimated by some to be on average eight years, places limits on the economic viability and lifespan of new molecules, discouraging innovation (Schmieder and Edwards, 2012). The lack of new antibiotic substances reinforces the importance of preserving those already in existence.
A pattern of antibiotic restrictions
Historically, motivations for antibiotic use in animal husbandry fall into three categories: growth promotion, disease prevention and treatment. The trend when it comes to governmental restrictions on antibiotics has been rather clear: antibiotics for growth promotion will be discouraged. (See callout box 'The G20 aims to limit antibiotics').
Countries looking to limit the application of antibiotics in animals typically start with restrictions on one or several antibiotic growth promoters (AGPs) often followed by a ban on AGPs. At least 32 countries have imposed a nationwide ban on AGPs, and 35 have a veterinary prescription requirement.
As a second step, some –though not all– countries then look to address preventive or prophylactic antibiotic use—thereby limiting the use of antibiotics to treat disease. Yet, these alone are not always sufficient to reduce antibiotic use in livestock.
Figure 2. The move toward prudent antibiotics use
The European example
In 2005, Europe banned the use of AGPs. For the regulators, the ban did not initially have the intended effect—namely, the reduction of antibiotics applied in livestock. The elimination of AGPs was met with a rise in prescribed veterinary antimicrobials for preventive use in subsequent years (Figure 1).
To address the preventive use of antibiotics, regulators in several European countries introduced a so-called 'yellow card' system that uses a series of different metrics to encourage further reductions in antibiotic use for preventive reasons.
This system proved effective in restricting antibiotic use to disease treatment (Figure 2), which explains why within Europe, Northern European countries have comparatively lower levels of antibiotic use in animals, taking into consideration the amount of antibiotics sold and size of the respective animal populations—referred to as a population correction unit (PCU) basis (Figure 3).
Figure 3. Sales of veterinary antimicrobials for food producing species in 2014
Prevalence of resistance in poultry
Numerous monitoring programs that survey levels of antibiotic-resistant bacteria in animals exist throughout the world. Aggregating surveillance data from 19 countries that record antimicrobial resistance of E. coli in poultry shows that countries such as Norway and Sweden that have less intensive antibiotic use (Figure 3) also have lower levels of E. coli resistant to antibiotics including ampicillin, ciprofloxacin and tetracycline (Figures 4, 5 and 6). This observation, along with continued pressure from consumers frequenting retailers and fast food outlets, increases the likelihood that more countries will eventually move to restrict antibiotic use to disease treatment.
Progress varies by country
Based on the number of antimicrobial-resistant E. coli in poultry, and taking into account the historical path that early-mover countries have taken towards antibiotic reduction and removal, we can broadly observe three sets of situations.
In the first group of countries –including Vietnam, the United States and several in South America– the process of antibiotic exit has yet to begin or is still in the early stages. In these countries, we often see high levels of resistance for many classes of antibiotics.
In the second group, AGPs have been banned, though they have yet to adopt a yellow card system or other measures to further clamp down on antibiotic use. In these countries –including Italy, Spain and Turkey– we can still find high levels of resistant E. coli, at least to a selected list of antibiotics.
In the third group of countries, where the prudent use of antibiotics is already implemented –including most of the countries in Northern Europe– resistance levels are considerably lower than elsewhere in the world.
Figure 4. Percentages of tetracycline-resistant E. coli isolates from poultry
Figure 5. Percentages of ciprofloxacin-resistant E. coli isolates from poultry
Figure 6. Percentages of ampicillin-resistant E. coli isolates from poultry
At least 32 countries have imposed a nationwide ban on antimicrobial growth promoters, and 35 have a veterinary prescription requirement.
The road ahead
The challenge for producers who have adopted antibiotic exit programs or find themselves in countries where antibiotic use is being curtailed, is to reduce antibiotics while keeping performance high. Alternative measures are required to substitute the role of antibiotics in relation to growth promotion and disease prevention if they are to retain their necessary role in disease treatment.
In modern animal production, there is a need for growth promoters in feed, just as there is a need for disease prevention. Some combination of feed additives, enhanced biosecurity, vaccination programs and better management practices will be the way forward—as evidenced by producers and geographies that have already made the switch.
Looking ahead, the key to addressing the antibiotics question will be to control resistances and close the performance gap.
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Danish Integrated Antimicrobial Resistance Monitoring and Research Programme. (2015). Use of antimicrobial agents and occurrence of antimicrobial resistance in bacteria from food animals, food and humans in Denmark. Report available from: www.danmap.org
European Medicines Agency, European Surveillance of Veterinary Antimicrobial Consumption. (2016). Sales of veterinary antimicrobial agents in 29 European countries in 2014. EMA/61769/2016.
Organisation for Economic Co-operation and Development. (2016). Antimicrobial resistance: Policy insights. Organisation for Economic Co-operation and Development.
Schmieder, R and Edwards, R. (2012). Insights into Antibiotic Resistance Through Metagenomic Approaches. Future Microbiology. 7(1):73-89.
World Health Organization. (2011). Tackling antibiotic resistance from a food safety perspective in Europe. World Health Organization.
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Article made possible through the contribution of Franz Waxenecker, Nataliya Roth and BIOMIN Holding GmbH