Antimicrobial Resistance and Livestock: What you need to know to reduce the spread of resistance (especially if you raise animals)

When people (and our animals) get seriously ill from a pathogen such as bacteria, we want to believe that the doctor (and veterinarian) has an antibiotic available to help them fight the disease and recover.  However, antibiotic resistant diseases that no longer respond to standard treatments are developing rapidly and threatening our health care systems world wide. Many of these resistant diseases first appear in livestock operations, and then spread to humans.

In the global hotspots where antimicrobial resistance is rapidly increasing, researchers found that the number of compounds with resistant strains tripled among chickens and pigs from 2000 to 2018 (1). The most used animal antibiotics (tetracyclines, sulfonamides, and penicillins) had the highest resistance rates. Much of the time these drugs are not being used to treat sick animals, but are used as growth promoters and as preventive measures in overcrowded industrial animal production units. This overuse of animal antibiotics is generating a global health crisis for humans as these antibiotic resistant genes find their way from livestock into the food supply and into people.

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Therefore antimicrobial resistance is a farm to table issue.  That means that at any point along the supply chain, from where the food is produced until the time it is served to someone who eats it, there is the potential for resistant microbes to get into the food system and cause disease. 

If you grow food on your farm, whether it’s just for your family or for sale to others, then you need to understand how antibiotic resistance spreads and what you can do to protect your livestock, family and the people who live around you.  Simply avoiding the use of antibiotics on your farm may not be enough to leave you free and clear of the antimicrobial resistance problems. Action and awareness are needed at every level of the food supply chain to ensure that we are slowing the spread of resistance and protecting our limited supply of life-saving antibiotics.

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What is antibiotic resistance?

The world is full of microbes, also known as microorganisms. Some are good and some are bad, at least in terms of what they do to humans.  The “bad microbes” are the ones that can cause disease in humans (or animals), and these pathogens may be in the form of a virus, fungus, bacterium, or protozoan (2).

Only some of the “bad” microbes can be treated with antibiotics, which are drugs that can kill off microbes.  Antibiotics are not specific, meaning they wipe out all susceptible microbes, good and bad alike, when you take them or when they are used to treat sick animals.  This is why sometimes you develop secondary problems such as yeast infections after taking antibiotics to treat some other disease.  The good microbes that have been keeping you healthy are wiped out by the drugs along with the bad and others will flourish in their absence.  You need time to regenerate and recover both from the disease and from the drug used to treat it.

Sometimes antibiotics do not kill all the pathogens.  There can be many reasons why this happens.  Perhaps the antibiotic dosage was too weak, the duration of the treatment was too short, or some change in the microbe allowed some to survive against the odds.  The microbes that survive treatment can continue to grow and develop, and continue to cause disease.  If this process gets repeated, then over time a strain of resistant microbes can develop.  In other words, these are microbes that can now withstand exposure to an antibiotic that used to kill them and they are now said to be antibiotic resistant microbes (3)

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Further complicating the situation, some bacteria are able to pass on their antibiotic resistant traits to other bacteria in a process known as horizontal transmission (4).  This can accelerate the rate at which antibiotic resistance develops. 

Once microbes are resistant to an antibiotic, that antibiotic is no longer useful to treat sick animals and humans.  New drugs are needed, and new drugs are not being developed fast enough to address this problem (5).

What are the consequences of a disease outbreak?

If antibiotic resistant strains of E. coli or other pathogens are involved in a disease outbreak, this vastly complicates the treatment of anyone getting sick.  Antimicrobial resistant pathogens can result in extensive hospital care, longer recovery times, and increased likelihood of dying (4).  As more and more pathogens develop resistance, this becomes a global health care challenge!

How are antibiotic resistant microbes transmitted from animals to people?

Animal diseases that can be transmitted to people are called zoonotic diseases, or zoonoses. More than half of all diseases that people deal with have come from animals and three-quarters of all emerging infectious diseases (like Covid-19) have animal origins (6). Even though antibiotic use for animals has seen increasing regulation and oversight since 1999, the spread of antimicrobial resistance continues to threaten us all (7). The overuse of antibiotics in livestock that occurs in any part of the world, can result in resistant microbes that can rapidly spread in our heavily interconnected food systems.

Animals can transmit antibiotic resistant microbes to people either directly or indirectly.

Direct Transmission.  People may become ill from handling a sick animal, or by consuming animal products (such as meat, eggs, milk, cheese, etc.) that have been contaminated at the site of infection or during processing.

Indirect Transmission.  People may become ill from handling the bedding, manure or spilled feed used by an infected animal.  Resistant microbes can sometimes be transmitted through the air, by breathing in dust or aerosolized particles.  They can also be transmitted via contaminated water, such as when manure leaches into the water system. Although transmission of antibiotic resistant microbes through vectors like mosquitoes is still considered rare and unlikely, scientists have recently detected antibiotic resistant bacteria in mosquitoes in the field (8). Usually mosquitoes and other vectors of zoonotic diseases transmit viruses (which do not respond to antibiotics anyway), but finding resistant bacteria in mosquitoes does raise some cause for concern about the future of vector-transmitted antibiotic resistant microbes.

What does this mean in practice on the farm?  

Handling a sick animal, or its manure, bedding or feed, can facilitate the transfer of pathogens from the animal to you, or to the air, water or other products on the farm.  Therefore it is critical that good hygiene is practiced when handling a sick animal, whether you intend to treat them with antibiotics or not.

An example of cross-contamination can be seen with the recent food recalls for Romain lettuce contaminated with E. coli (9).  Lettuce cannot get sick from E. coli and so it is not the source directly.  But a field that has been improperly fertilized with animal manure or lettuce that has been washed in water contaminated by manure can end up with enough E. coli present to make people sick when they eat the lettuce.  This means that it is not just animal products that can pass on antibiotic resistant microbes, but all kinds of foods that may get exposed somewhere along the supply chain on their way to your table.

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But I don’t use antibiotics to treat my animals, so I am safe right?

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WRONG.  Livestock and farm life actually create exposure risks to antibiotic resistant microbes even if you, yourself, do not use antibiotics to treat your animals.  Some potential sources of antibiotic resistant microbes on the farm include:

  • Purchasing livestock from an industrial farm
  • Rodents, birds and other wildlife that may transmit a resistant pathogen to your stock
  • Contaminated water sources
  • Airborne particles from neighboring farms or farms that you visit
  • Manure brought in from another farm for compost or fertilizer
  • Feed that is contaminated with manure

So just because you don’t use antibiotics on your farm doesn’t mean you can forget about antibiotic resistance!

Every farmer needs to be practicing due diligence and working to stop the spread of antimicrobial resistance through the food chain.

How can you reduce the spread of antibiotic resistant microbes?

Remember the One Health approach:  The health and welfare of your animals and the environment is ultimately tied to your health!

We sink or swim together when it comes to antibiotic resistance. The diseases and the antibiotics needed to successfully treat them are the same for animals and for humans. We cannot afford to get this wrong.

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Where you spend time ultimately affects the amount and type of antibiotic resistant genes you carry. A 2020 study showed that a sample of 14 veterinarian students interning at industrial pig farms in China underwent changes in their gut microbes after being exposed to resistant genes, picking them up from the environment on the farm during the course of their work (10).  These changes persisted for several months after the exposure.

What you do and where you go shapes the microbes and antimicrobial resistant genes that you carry.  Make your farm a safe place to be by focusing on antimicrobial stewardship.

Here is what you can do to help stop the spread of antimicrobial resistance:

Wash your hands!  Wash your hands.  Wash your hands . . .. .it deserves repeating!  Always wash your hands after handling animals, bedding, feed or manure to ensure you are not spreading microbes.  Plain soap and water is sufficient to kill pathogens, including antibiotic resistant types.  For the full details, read the CDC’s post: Show me the Science – Why Wash Your Hands?

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Use personal protective equipment. If there is any doubt about the potential of a sick animal to transmit the disease to you, use PPE like gloves, masks, disposable overalls, etc. to protect yourself.

Use antibiotics correctly. If you have sick livestock, use antibiotics under the supervision of a veterinarian. Do not use antibiotics as growth promoters.

Avoid medicated feeds. Medicated feeds provide small doses of medicines in an effort to ward of illness. Instead, focus on improved animal husbandry, breeding for disease resistance, or switching to livestock that are better suited to your conditions and climate.

Purchase livestock with added care.  Find out the health of animals prior to bringing them home and whether they have received antibiotics or medicated feeds.  Remember to isolate (quarantine) new animals away from your main stock for a period of two to four weeks to watch for signs of illness.  Practicing good biosecurity measures can help reduce the spread of disease from new animals.

Handle manure and bedding from sick or infected animals with caution.  Composting can effectively reduce the antibiotic resistant gene load of manure. A 2020 study published in the Journal of Hazardous Materials reduced the presence of antibiotic resistant genes in cow manure by 83% via aerobic composting for 14 days (11).  Another 2020 study published in the journal Environmental Science and Pollution Research found that 10 weeks of composting chicken manure was sufficient to significantly reduce the presence of pathogens, including antibiotic resistant microbes (12)Always compost manure thoroughly before using it on other food crops.

Improve your husbandry.  Provide ample space, shelter, food and water for each animal to reduce stress.  If you have repeated disease issues, then it can be useful to audit your animal handling and care procedures to look for ways to prevent the disease rather than having to treat sick animals after the fact.

Stop breeding susceptible livestock.  Good breeding standards include the selection for disease resistance.  Remove animals that have required treatment for disease from the breeding pool to select for disease resistance.  If you have ongoing disease issues, consider changing the breed or type of livestock you raise to better match your conditions and climate. There are many hardy and disease resistant animals to choose from, particular among the heritage breeds (13).

Use the sun.  UV radiation from the sun kills most pathogens (14).  Carry perches, nest boxes, feed tubs and other equipment out into the sun to take advantage of some free antimicrobial help.  Designing animal shelters so that they can be opened to let in sunlight is a useful tactic for reducing pathogens on the farm.

Try natural health boosters.  Some livestock benefit greatly from the use of antimicrobial support such as essential oils, vitamins, antioxidants and fresh whole foods that provide key micronutrients and immune system boosters.

Essential oils for chickens

Use food safe practices. Ensure that you understand safe and effective food handling procedures that minimize contamination and reduce the growth of potential pathogens on foods as they are harvested, stored, or prepared for market or your table.

In Summary

Antimicrobial resistance represents a significant health risk to people around the world.  The overuse of antibiotics in livestock has been contributing to the record rate at which resistance is developing for some of our best disease-fighting drugs.  Antibiotic resistant disease organisms can be transmitted directly and indirectly to people and into our food supply. Even if you do not use antibiotics on your farm, you may not be safe from exposure or risk, depending on your farm practices and sources of livestock. Creating an antimicrobial stewardship plan for your farm can be as simple as implementing important safety measures and practices.

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