Three-quarters of antibiotics are used on animals. Here's why that's a major problem

Antimicrobial resistance (AMR) — that is, a declining effectiveness of medicines to treat bacterial infections — is identified by the World Health Organization (WHO) as one of the greatest threats to global health, development and food security.1 AMR occurs when bacterial populations evolve in the presence of an antibiotic medicine; this leads to treatments becoming either less efficient or completely ineffective.

A number of infections, including pneumonia, tuberculosis, and salmonellosis are already showing increasing resistance to antibiotic treatment, making them more difficult to treat.2

Although AMR arises naturally as bacteria encounter antibiotics, the overconsumption of these medicines is accelerating the process. In addition to the overuse of antibiotics in human medicine, their use for livestock farming is also linked to resistance in humans.3 Antibiotics used in agriculture can be ingested by humans through food consumption.4 Furthermore, it’s estimated that up to 90 percent of antibiotics consumed by animals are excreted — releasing them into the natural environment for dispersal in ground and surface waters.5 In 2016, the UN General Assembly recognised the use of anitbiotics in the livestock sector as one of the primary causes of antimicrobial resistance.6

This post takes a look at the data on the global use of antibiotics in livestock, and what can be done to limit its impacts on global health and antimicrobial resistance.

Global use of antibiotics for livestock

Use of antibiotics for livestock greatly exceeds that of uses for humans: Although data collection on antibiotic use in some regions is poorly documented, its estimated that global veterinary consumption of antibiotics in 2013 was around 131,000 tonnes. In relative terms, antibiotic use in livestock and humans is similar, averaging 118 mg/PCU (population-corrected unit, explained below) and 133 mg/kg, respectively.7 However, since total livestock biomass greatly exceeds that of human biomass, total antibiotic use for humans is estimated to be much lower — around 40,000 tonnes in 2013.8 This means antibiotic use in livestock is likely to account for approximately 70-80 percent of total consumption.

But why do we use antibiotics in agriculture? Like humans, animals are susceptible to bacterial infection — antibiotics are therefore used to treat infected animals. However, their application now extends beyond this. For farmers, often with large populations of animals (which increases the likelihood of bacteria spreading if one animal is infected), it is a priority to make sure that their livestock are in optimum health. The mass use of antibiotics as a preventative measure (rather than as a treatment) has therefore become increasingly common. In addition to their use for infection treatment or prevention, antibiotics are, in some countries (although banned in others, such as the EU) added to animal feed in order to enhance animal productivity and meat yields. This revelation that the supplementation of animal feed with antibiotics led to increased growth was a largely spontaneous discovery in the 1950s.9

Antibiotics use is commonplace across the world. In the chart below we see the consumption of antibiotics in livestock in 2010 (latest available data at national levels) across a range of countries.10 Since levels of meat production vary significantly across the world, these metrics are reported in milligrams of total antibiotic ingredient used per kilogram of meat production. This is corrected for different livestock species and sizes, giving a population-corrected unit (PCU). This allows us to compare rates of antibiotic use across the world.

As shown, there are large variations between countries, ranging from only 4 milligrams per kilogram in Norway, to greater than 200 milligrams in Cyprus, Spain, Italy and Germany in 2010.

General disclaimer:

The designations employed and the presentation of material on this map do not imply the expression of any opinion on the part of the World Economic Forum concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

Regulatory successes: how to reduce antibiotic use

It’s expected that as global meat consumption continues to rise, and low-to-middle income nations shift towards more intensive livestock methods, total antibiotic use in livestock will increase from 131,000 tonnes in 2013 to just over 200,000 tonnes in 2030.11 This increase poses a significant threat to the effectiveness of antibiotic medicines. The UN have issued extensive guidelines on their use in livestock and published a ‘strong recommendation’ for overall reduction in the use of medically-important antibiotics in livestock.12

How do we reduce our consumption of antibiotics in livestock? Effective regulation on antibiotic use has proven highly successful in reducing rates of use across several European countries.
Most European countries now collect annual data on antibiotic use and trends for several countries are shown in the chart below.

Rates in Scandinavian countries — Norway, Finland, Sweden and Denmark — are 50-100 times lower than in other European countries such as Cyprus, Spain and Italy. In the 1990s and early 2000s, the Scandinavian nations phased out the use of antibiotics for growth promotion (called ‘antibiotic growth promoters; AGPs’).13 This led to a significant decline not only in antibiotic use for growth, but also for therapeutic uses. These countries maintain very low levels of antibiotic use partly through a combination of good practices for livestock health (reducing the demand for treatment) and regulatory restrictions.

In 2006, the European Union (EU) banned the use of antibiotics for non-medicinal purposes. This has had varying success in reducing consumption across the EU and while in some countries we do not see a decrease there are other EU countries in which we have seen a significant decline after this ban: Germany, France and the United Kingdom have all seen declines in antibiotic use through tightening monitoring and reporting requirements. The UK set a target of reducing consumption below 50mg/kg of meat by 2018; it reached this target two years ahead of schedule.14

Addressing the threat of AMR will require such reduction efforts to extend globally. Van Boeckel et al. (2017) analysed a range of potential reduction scenarios for the year 2030 (these are further discussed in additional information at the end of this blog).15 One key mechanism for reduction was setting a global cap of 50 milligrams per kilogram of meat production. In the chart below we have categorised countries based on whether their antibiotic use in 2010 fell above or below this 50mg/PCU suggested cap.

Typically rates of antibiotic use are larger for higher-income nations, and those with higher levels of meat consumption. However as discussed above, there are some notable exceptions, being lowest in Norway, and also low in Finland, Sweden and Denmark — high-income nations with effective regulation. With good agricultural practices and effective policies, such examples highlight that significantly reduced antibiotic use (and risk of resistance) can be achieved alongside highly productive agricultural sectors. The two are compatible.

General disclaimer:

The designations employed and the presentation of material on this map do not imply the expression of any opinion on the part of the World Economic Forum concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

Additional discussion:

How to reduce antibiotic use
Van Boeckel et al. (2017) projects that under expected rates of antibiotic use and growth in global meat consumption, antibiotic use will increase to just over 200,000 tonnes in 2030 (here, termed ‘business-as-usual’). There are two key mechanisms by which we can reduce total antibiotic consumption: decrease the quantity of antibiotic use per unit (kilogram) of meat production; and/or decrease our overall meat consumption.

Van Boeckel et al. (2017) analysed a range of reduction scenarios to see how effective each would be in reducing total antibiotic use.16 These reduction scenarios are based on two options for reduction: either setting a limit on rates of antibiotic use to 50 milligrams per kilogram of meat (a target now adopted by several European countries); or reducing overall meat consumption per capita. A highly ambitious meat reduction target to 40 grams per person per day has been proposed (which is in line with China’s more recent meat guidelines), or alternatively a less stringent reduction to 165 grams per person (the projected EU average level in 2030). Below we look at how either of these options may be achieved. Different approaches to reduction have variable levels of effectiveness. The scenarios in the chart are ordered by increasing effectiveness. These are:

achieving a global level of meat consumption of 165 grams per person per day (the projected average level of meat consumption in the EU in 2030) would reduce antibiotic use by 22 percent;

setting a limit of antibiotic use in OECD countries and China of 50 milligrams per kilogram of meat (50mg/PCU) would reduce consumption by 60 percent. Boeckel et al. (2017) suggest this approach to achieve large reductions in antibiotic use without targeting farmers in lower-income countries who rely on livestock rearing for subsistence;

extending this 50 milligrams per kilogram (50mg/PCU) limit to a global level would reduce consumption by 64 percent;

the most effective approach would be to achieve a global average level of meat consumption of 40 grams per person per day (this is the guideline currently applied in China).17 This would achieve a 66 percent reduction.

These scenarios look at each mechanism individually, but there is of course options to combine these efforts. For example, if we all limited daily meat consumption to 165 grams per day and OECD countries & China capped antibiotic use at 50mg/PCU we would achieve the same as the most ambitious scenario above: reducing consumption by 66 percent.

How much would we have to reduce meat consumption?
The other option for limiting total antibiotic use is to decrease total meat consumption. The above scenarios suggested two daily per capita limits: 165 grams (the projected EU average in 2030) or 40 grams (for reference, this is the size of an average burger patty). Levels of meat consumption across the world are shown relative to these levels in the chart below (with red countries consuming more than 165 grams per day, yellow between 40-165 grams, and blue below 40 grams).

Currently, per capita meat consumption across many countries greatly exceeds even the less ambitious 165 gram target. Supply in the United States, for example, was greater than 300 grams per person in 2013. Attaining a global average of 165 grams with more equitable meat consumption across the world will therefore require significant reductions across many countries. Reaching the ambitious target of 40 grams would require a dramatic shift in global consumption habits. The United States would have to reduce meat consumption by 85-90 percent by 2030.

General disclaimer:

The designations employed and the presentation of material on this map do not imply the expression of any opinion on the part of the World Economic Forum concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

Footnotes

1. WHO (2017). Antibiotic Resistance Fact Sheet. World Health Organization. Available online.

2. Liu, Y. Y., Wang, Y., Walsh, T. R., Yi, L. X., Zhang, R., Spencer, J., … & Yu, L. F. (2016). Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological study. The Lancet infectious diseases, 16(2), 161-168. Available online.

WHO (2017). Antibiotic Resistance Fact Sheet. World Health Organization. Available online.

3. Aarestrup, F. M., Kruse, H., Tast, E., Hammerum, A. M., & Jensen, L. B. (2000). Associations between the use of antimicrobial agents for growth promotion and the occurrence of resistance among Enterococcus faecium from broilers and pigs in Denmark, Finland, and Norway. Microbial Drug Resistance, 6(1), 63-70. Available online.

4. Ventola, C. L. (2015). The antibiotic resistance crisis: part 1: causes and threats. Pharmacy and Therapeutics, 40(4), 277. Available online.

5. Centers for Disease Control and Prevention, Office of Infectious Disease Antibiotic resistance threats in the United States, 2013. Apr, 2013. Available online.

6. Van Boeckel, T. P., Glennon, E. E., Chen, D., Gilbert, M., Robinson, T. P., Grenfell, B. T., … & Laxminarayan, R. (2017). Reducing antimicrobial use in food animals. Science, 357(6358), 1350-1352. Available online.

7. Van Boeckel, T. P., Glennon, E. E., Chen, D., Gilbert, M., Robinson, T. P., Grenfell, B. T., … & Laxminarayan, R. (2017). Reducing antimicrobial use in food animals. Science, 357 (6358), 1350-1352. Available online.

8. This estimate is based on estimates from Van Boeckel et al. (2017) and Walpole et al. (2012). Van Boeckel note that antibiotic use rates in humans is comparable to that of livestock (113 milligrams per kilogram and 133 milligrams per kilograms, respectively). However, animal biomass greatly exceeds that of human biomass; human biomass was calculated based on an adult population of 5.45 billion and average mass of 62 kilograms in 2013.

Walpole, S. C., Prieto-Merino, D., Edwards, P., Cleland, J., Stevens, G., & Roberts, I. (2012). The weight of nations: an estimation of adult human biomass. BMC public health, 12(1), 439. Available online.

9. Although the specific mechanisms are not completely clear, it’s hypothesised that antibiotics repress intestinal bacteria. The reduction in microbial fermentation processes within the gut decreases energy expenditure and allow for a greater proportion of animal feed to be converted into animal biomass.

10. Van Boeckel, T. P., Brower, C., Gilbert, M., Grenfell, B. T., Levin, S. A., Robinson, T. P., … & Laxminarayan, R. (2015). Global trends in antimicrobial use in food animals. Proceedings of the National Academy of Sciences, 112(18), 5649-5654. Available online.

11. Van Boeckel, T. P., Glennon, E. E., Chen, D., Gilbert, M., Robinson, T. P., Grenfell, B. T., … & Laxminarayan, R. (2017). Reducing antimicrobial use in food animals. Science, 357 (6358), 1350-1352. Available online.

12. WHO guidelines on use of medically important antimicrobials in food-producing animals. Geneva: World Health Organization; 2017. Licence: CC BY-NC-SA 3.0 IGO. Available online.

13. Grave, K., Jensen, V. F., Odensvik, K., Wierup, M., & Bangen, M. (2006). Usage of veterinary therapeutic antimicrobials in Denmark, Norway and Sweden following termination of antimicrobial growth promoter use. Preventive veterinary medicine, 75(1), 123-132. Available online.

14. UK-VARSS 2016; UK – Veterinary Antibiotic Resistance
and Sales Surveillance Report (2017). Available online.

15. Van Boeckel, T. P., Glennon, E. E., Chen, D., Gilbert, M., Robinson, T. P., Grenfell, B. T., … & Laxminarayan, R. (2017). Reducing antimicrobial use in food animals. Science, 357 (6358), 1350-1352. Available online.

16. Van Boeckel, T. P., Glennon, E. E., Chen, D., Gilbert, M., Robinson, T. P., Grenfell, B. T., … & Laxminarayan, R. (2017). Reducing antimicrobial use in food animals. Science, 357 (6358), 1350-1352. Available online.

17. Wang, S. S., Lay, S., Yu, H. N., & Shen, S. R. (2016). Dietary Guidelines for Chinese Residents (2016): comments and comparisons. Journal of Zhejiang University-SCIENCE B, 17(9), 649-656. Available online.