Farmers in the US are using more antibiotics on farms, particularly in pigs and cattle, than they did seven years ago when their use to boost animal growth was prohibited. Scientists and veterinarians worry that excessive use of antibiotics on farms is furthering antimicrobial resistance. (Photo: iStock)

Antimicrobials are widely used to treat or prevent disease in farm animals across the US. More of these medically important drugs are sold for use in livestock than for humans each year. Using antimicrobials gives illness-causing bacteria a chance to develop ways to evade them—a problem that killed 1.14 million people globally in a single year, topping deaths from HIV and malaria combined. What’s more, mortality is expected to grow by nearly 70% over the next 25 years, reaching a similar scale to the COVID-19 pandemic.

To tackle the crisis, nearly 8 years ago the US Food and Drug Administration (FDA) effectively banned farmers from using medically important antimicrobials to boost growth in livestock—a practice regarded by many researchers, veterinarians and advocates as excessive and unnecessary. Antimicrobials are a group of drugs that kill microorganisms including bacteria, viruses, and fungi. 

The FDA contends that the widely welcomed ban, along with some other reforms, have led to “significant and sustained” changes in the use of antimicrobials on farms.

But advocates for cutting the use of antimicrobials warn that the FDA’s assertions are “disingenuous”.

New data shows sales are falling, says FDA 

Using fewer antimicrobials is crucial to help preserve important medicines for the good health of people and animals, say scientists. “Every time we use an antimicrobial, microorganisms are going to adapt and resistance can develop,” says Javier Yugueros-Marcos, head of antimicrobial resistance at the World Organization for Animal Health (WOAH), the global authority on animal health based in Paris, France.

Every time we use an antimicrobial, microorganisms are going to adapt and resistance can develop – Javier Yugueros-Marcos, head of antimicrobial resistance at the World Organization for Animal Health

At a meeting at the United Nations in September, global leaders acknowledged that antimicrobial resistance is one of the most urgent global health threats and promised to “meaningfully reduce” the amount of antimicrobials used in animal agriculture globally over the next 6 years to help tackle the crisis. However, they failed to set clear targets to lower use following push back from the United States and other meat producing nations. 

The FDA says its efforts are gaining ground. On 10 October, the agency published new data that it says suggests a healthy overall downward trend in the volume of antimicrobials sold for use in livestock. Annual sales of antimicrobials are often taken as a rough indication of the amount used in farm animals, although not all drugs sold will be consumed. (The FDA doesn’t yet routinely collect data on how much antimicrobial farmers actually use). 

In a summary analyzing the new data, the FDA highlights that sales fell by 2 percent from 2022 to 2023 and by 37 percent since 2015. Most of these gains come from a big drop in sales as farmers geared up to meet the ban on using antimicrobials to boost growth. 

In a statement to US Right to Know, an FDA official wrote that the agency believes “the overall trend in volume of sales indicate a significant and sustained change in how antimicrobials are sold and distributed in food-producing animals.” 

But veterinarians and advocates for cutting antimicrobial use in farm animals warn that sales are actually growing for some livestock species. 

Steven Roach, who works on safe and healthy food at the Food Animal Concerns Trust (FACT), a campaign group, says that after an initial welcome drop, sales began to rebound after the ban came into force.

“We can all agree that what the FDA did had an impact,” he says. But the impact is limited and the drop in sales wasn’t big enough, he adds.

Roach calculated a small drop in sales between 2022 and last year but a 6.9 percent rise from 2017. His calculations take account of changes in the size and weight of livestock populations, clarifying that shifts in sales are not due to fluctuations in animal numbers. 

The initial drop in US sales is largely due to big cuts made in chicken and turkey farming with the former sector slashing sales in half since 2017 and dropping a further 4.6 percent between 2022 and last year, says Roach. 

Less progress is seen in pigs and cattle. Roach calculated a small drop in sales for pigs between 2022 and 2023, but a 24 percent rise since 2017. Sales for cattle rose by 1.5 percent between 2022 and 2023 and jumped by 10 percent since 2017, he says. 

Gail Hansen, a public health veterinarian and former state epidemiologist and public health veterinarian for the Kansas Department for Health and Environment, agrees. “Things are creeping back up,” she says.

Randall Singer, a veterinarian and epidemiologist who researches antimicrobial resistance in poultry at the University of Minnesota, says that the poultry industry—with which he works closely—has reduced its use of antimicrobials “almost to the bare minimum”. But notes that the use of antimicrobials will fluctuate as diseases ebb and flow.

Farmers of other livestock species should reassess their use of antimicrobials, he says. But they must take care when changing their practices.

“You keep tweaking the system until you know that you can safely pull that antibiotic practice out of your system and not have the consequence of severe animal health and welfare issues,” he says. 

David Wallinga, formerly a physician and scientist at the Natural Resources Defense Council—an environmental organization —also found upward trends in sales in research that he co-authored.   

Wallinga, who now sits on the steering committee of Keep Antibiotics Working, an advocacy group based in the US, says the FDA is “unnecessarily soft on the major corporations” that promoted overuse of antibiotics on farms and has fallen short of its “weak promises” to tackle the problem. Consequently, US farmers are lagging behind their European counterparts.

Farmers in Europe stopped using antimicrobials to boost growth over a decade prior to those in the US. They also no longer use antimicrobials routinely to prevent disease. Antimicrobials on European farms have dropped by around 43 percent over nine years up to 2020 at which point use on the continent was over 80 percent lower than in the US, Wallinga’s research shows. 

In contrast, routine use of antimicrobials is common on US farms particularly in intensive and confined operations where large numbers of animals are housed in close quarters and animal welfare and sanitation standards are lower, says Hansen.

Wallinga says the FDA’s assertions that it has achieved large and sustained cuts in antimicrobial use and resistance are “disingenuous”.

“The Center for Veterinary Medicine chooses to act in subtle ways to veil their misdirection and inaction in a smokescreen of unclear language, excuses, and lack of transparency,” he says of the FDA body in charge of regulating animal medicines and which leads the agency’s efforts on antimicrobial resistance. 

The Center for Veterinary Medicine chooses to act in subtle ways to veil their misdirection and inaction in a smokescreen of unclear language, excuses, and lack of transparency – David Wallinga, a physician and steering committee member of Keep Antibiotics Working.

In a statement to US Right to Know, an FDA official acknowledged that sales rebounded after the ban—which the agency puts at around 9 percent between 2017 and 2018—but says that numbers have remained relatively stable at a reduced level since then.

“It would be unrealistic to expect sales of medically important antimicrobials for food producing animals to decrease every year,” the official adds. 

The FDA says that its efforts to cut antimicrobial use are associated with reductions in resistance among key bacteria—principally Escherichia coli (E.coli) and Enterococcus. The former is a common bacteria that infects the intestines of people and livestock causing diarrhea, urinary tract infections and pneumonia. The latter can also infect the urinary tract and the lining of the heart. 

Scientists suggest that as the use of antimicrobials drops, resistance should also drop, although a direct link between cutting drug use and reducing bacterial resistance is difficult to prove. 

In a letter dated 17 September, the agency told U.S. Senator Cory Booker (D-NJ) that “a concomitant decline in resistance” among these bacteria are “important indicators of change”.  The FDA’s comments were in response to a letter from Sen. Booker asking the agency for a progress report on its strategy to tackle antimicrobial use in livestock.  

But researchers say that reading trends in resistance to antimicrobials isn’t straightforward.

Independent academic research, and data from the National Antimicrobial Resistance Monitoring System (NARMS), a collaborative program run by the government, state and local public health departments and universities, shows that resistance to antimicrobials is falling for some bacteria and some drugs but rising for others. 

And resistance in poultry and cattle is faring better than in swine.

Csaba Varga, an infectious disease epidemiologist who researches antimicrobial resistance in animals and people at the University of Illinois Urbana-Champaign, says that resistance to the most crucial antimicrobials such as cephalosporins that treat infections like pneumonia and meningitis, generally remains low. But there are some worrying shifts, he says.

In research published last year, Varga found rising resistance to cephalosporins in E. coli samples taken from pigs. He also found E.coli with very high resistance to other less critical antibiotics like ampicillin, a penicillin derivative used to treat infections like meningitis.

Varga also notes a “concerning” emergence of resistance to fluoroquinolones—another critical group of antimicrobials—in Campylobacter, a bacteria commonly found in undercooked poultry and other meats that can cause severe gastrointestinal infections in people. He is also worried about evidence of growing resistance in Salmonella, another common cause of food poisoning, to beta-lactam antibiotics, a class which includes cephalosporins.

Madeleine Kleven, an analyst for FACT, says that looking at the proportion of drug groups with no resistance to bacteria such as E.coli can also show how they are holding up. The NARMS data show that the percentage of chicken samples with no resistant E.coli is growing but in swine it’s dropping, she says. 

“Whatever the chicken industry is doing is working,” she says.

Mohsen Naghavi, a health metrics scientist at the University of Washington in Seattle, who works on antimicrobial resistance, says that it’s difficult to parse an overall picture of the battle against antimicrobial resistance by looking at trends in bacteria. “Every pathogen and drug combination has a separate story,” he says.

Instead, he prefers to gauge progress by looking at patterns in human mortality from antimicrobial resistance. Globally, more people are dying from it today than three decades ago. Between 1990 and 2021, deaths from antimicrobial resistance grew by 80 percent in people 70 years and older but fell by around 50 percent in children younger than 5 years, leading to a slight increase in overall mortality.  . 

An FDA spokesperson said in a statement that the agency’s responses to Senator Booker’s letter “adequately summarize” its accomplishments and the challenges it faces.

But to understand the impact the policies have had, research is needed to compare the resistance patterns before and after the policy changes, says Varga.

To make real headway in the battle against antimicrobial resistance, US farmers must further reduce their need for antimicrobials by improving living conditions and the welfare of animals in intensive farming operations, including by reducing animals’ stress, the density in which they are kept and vaccinating them against diseases, says Yugueros-Marcos. These improvements will help prevent infections from occurring in the first place, says Naghavi.

“Preventing infections is the most important factor for the control of antimicrobial resistance. When you do not have infections you do not have resistant bacteria,” he says. The FDA must acknowledge that these kinds of changes are needed to ensure healthier animals on US farms, says Wallinga. Instead, the FDA “echoes the industry claim that continuing the routine use of antibiotics is necessary for animal health.”