Are You Chicken of Antibiotics?

Mar 29, 2017 | Food and Nutrition | 0 comments

The Dirt:

Many of us would not be alive today without antibiotics. While antibiotics have certainly been a life-saver, there is also a downside to overuse. What is the healthy balance? And how do animals treated with antibiotics affect this balance? Many organic organizations often argue that giving animals antibiotics ultimatly leads to human resistance. Is there any truth to this? Let’s find out…

Hey D2D readers— you may be thinking…antibiotics in animals?! Haven’t I read this already?? Well, yes, this has been a topic covered on the blog. But, the research is constantly updating and therefore we need to amend old articles to remain a reliable, up-to-date source for you all. Enjoy…

The following questions have been the subject of several differences in opinion focusing on animal agriculture for antibiotic resistance.

  • Is my body becoming resistant to antibiotics just by eating a steak, chowing down a turkey sandwich, or drinking a glass of milk?
  • Are animals the cause of antibiotic resistant strains of superbugs like tuberculosis, pneumonia, or MRSA (staph infections)?
  • Is it humane to withhold antibiotics from animals when they are sick?

The answer to to all three is NO.

Antimicrobial resistance (AMR) is a real and dangerous threat to all of us. Antibiotics given to animals and poultry for both disease and animal growth have been blamed for creating “super bugs” that resist antibiotic treatment thus creating a danger to humans. But these claims are largely unsubstantiated.

Billions of people—and animals—depend on antibiotics to get healthy if experiencing an illness. We imagine that everyone who is reading this post has been treated with these miracle drugs for some type of bacterial infection. However, because some bacteria are mutating faster than new drugs are being created, superbugs have become a global health concern. Every year in the United States alone, 2 million people are infected with an antibiotic resistant strain of bacteria and roughly 23,000 die. The CDC published a report listing 18 different drug-resistant threats in the United States. These threats are categorized into: urgent, serious, and concerning. Some of the most common and dangerous strains are MRSA, streptococcus pneumoniae, VRE, and CDIFF. And when these microbe become resistant to more than one antibiotic, the threat to human health becomes even more dire.

First, how do antibiotics kill bacteria?

In 1928, Alexander Fleming accidently discovered penicillin. He came back from a vacation to see that a fungus (Penicillium notatum) had eliminated some of a Staphylococcus bacteria. Fast forward through many research trials and antibiotics became a wonder drug during WWII when they were used to save the lives of soldiers who acquired infections on the battlefields and in the hospitals.

Different types of antibiotics play different roles in eliminating bacteria, but the general theme is: they destroy certain structures that bacteria cells have but human cells do not. For instance, human cells do not have cell walls and bacterial cells do. Certain strains of antibiotics can eliminate the cell wall and the bacteria dies. Additionally, another strain of antibiotics blocks the ability of bacteria to synthesize DNA— a certain death sentence for the microbe. Some antibiotics prevent a bacterium from building its own proteins, which will prevent it from surviving. Each type of antibiotic has its own role for effectively eliminating infections.

Of course, antibiotics cannot distinguish between a friendly and harmful bacterium, which is why we don’t want to over-do the treatment. The proper balance of friendly bacteria helps keep our immune system strong. (This is something we have discussed in “Gut Microbiome: Your Second Brain”)

The Bacteria Mutation to Resistance

Bacteria, like any living organism, will react in response to a threat. In this case, they mutate. There is a constant war between microbes and the things they attack. (Think: Darwin’s survival of the fittest.) Bacteria and the things they infect (including the human body) are locked in an age old battle: organisms developing natural antibiotics and bacteria evolving to resist them. Unfortunately, bacteria are very robust and will often mutate without the presence of antibiotics. So, it is not surprising that antimicrobial resistance occurred long before humans discovered antibiotics.

Today, when large amounts of an antibiotic are present in the environment, it creates the ideal conditions to promote mutation and evolve resistance. Once this happens, the mutated strain can reproduce faster and pass along that mutation to all of its progeny— and inevitably you end up with a resistant strain of bacteria that becomes a threat to humans and/or animals.

What is to blame for Antimicrobial Resistance?

As we mentioned above, antimicrobial resistance (AMR) is a normal process that was happening long before humans developed antibiotics. Once a bacterium becomes resistant to an antibiotic (often by random mutation), it passes that resistance down to each of its offspring and can share these resistant genes with other bacteria (through trading small loops of DNA called plasmids.) Once humans figured out how to produce antibiotics in large quantities, the stage was set to accelerate the evolution of antibiotic resistance.

Now let’s be clear, the advent of antibiotics for human and animal use was perhaps the greatest medical breakthrough in history, alleviating the suffering of countless humans and animals. But this has come at a cost: the price being the evolution of bacteria resistant to medically important antibiotics.

Pre-Human Antibiotic Resistance

  • A microbiome culture was taken in Lechuguilla Cave, New Mexico. It had been isolated in a cave for 4 million years. Still, scientists found bacteria that was resistant to 14 antibiotics used today!
  • Resistance was found to penicillin and tetracycline just as they came onto the pharmacy shelf in the 1940s and 1950s.
  • Antibiotic resistant bacteria have even been discovered in a 30,000-year-old permafrost!

Farm production of cattle, pigs, and poultry has gotten the most attention because of the large amount of antibiotic use. This is because there are some antibiotics that are shared in both animal and human medicine. It seems logical. If we don’t give the same antibiotics to animals that humans use – then resistance won’t occur, right? Let’s examine this more carefully.

Why give antibiotics to animals or poultry anyway?

Antibiotics are given to animals for two purposes:

  1. To treat or prevent disease
  2. To stimulate animal growth

Remember, the antibiotics of concern (deemed medically important) are those that are shared in human and animal medicine. The antibiotics that are only used to treat animals and poultry are not of a concern for AMR (although they can become less effective antibiotics for animals) and this represents a large proportion of antibiotics used in agriculture.


Like humans, animals require medication when they get sick. As the animals’ caregiver, it is the owner’s responsibility to reduce their suffering. Farmers use antibiotics to treat illness and prevent diseases from spreading throughout the farm. Certainly, anyone who has ever cared for pets knows it is inhumane to withhold antibiotics from a suffering animal! For example, dairy farms use antibiotics to help treat a cow with painful mastitis (an infection in the mammary gland). Think about when you were sick and needed a Z-pack or amoxicillin to get over a bacterial infection? Well, imagine how you would feel if you had to persevere without it.

Tylosin is a common antibiotic used for poultry, cattle, and swine. For poultry, it is used to control a chronic respiratory disease. For cattle in the feedlot tylosin is used to treat liver abscesses. For pigs, it can control respiratory issues as well as arthritis. This is a shared class with the human antibiotic, Erythromycin, used to treat everything from acne to ear and respiratory infections. While it is not the exact same compound as tylosin, it is in the same class. Scientists are divided whether this is an issue for humans or not. Tylosin falls in the important but not critical category. It is also less than 7% of all the antibiotics sold to food production.

In addition to therapeutic antibiotics, low doses of antibiotics are also used as non-therapeutic “growth-promoters” in farm-raised animals. While the name can be misleading, these antibiotics do not directly help the animal grow, but rather they act on the bacteria inside the animal’s intestines and enable more of the animals’ bodily resources to go toward achieving maximum growth potential.

Tetracycline is the most common antibiotic used for animals comprising 70% of all animal antibiotics.  It is used as a growth promoter for cattle and it treats bacterial infections in pork, poultry, and cattle. While it is considered a shared class, commonly used to treat Lyme disease, acne, and cholera for humans, it is only comprises less than 4% of human antibiotics.

Like humans, animals require medication when their bodies cannot fight off disease-causing bacteria. Antibiotics also help prevent diseases from spreading throughout the farm.

The USDA recently reported that sales of antibiotics for agriculture increased by only 1% from 2014-2015. It is important to note that this is pharmaceutical sales and does not necessarily mean that all of them were actually used on the farm or in the feedlot.

And there are other factors to consider such as the different types of antibiotics used and whether there were swine or poultry disease outbreaks during that time period.

Moreover, there are more animals and birds grown in the United States in 2015 compared to 2009. 

But let’s separate out the issues…


Is antibiotic use in animals resulting in antibiotic residues in the food we eat?

First of all, the FDA has strict antibiotic use guidelines and requires that an animal be clear of antibiotics before that animal is harvested. This is referred to as the withdrawal time. The time varies depending upon the type of antibiotic used for the type of animal and the type of disease. But it is mandatory that all residues are out of the meat or dairy by the time it is harvested. The goal is to have all traces of antibiotics out of the meat by the time it is consumed.

Ok, so what so happens if the withdrawal period is not followed by the farmer? What is the risk if they don’t comply? Well, the meat and dairy industries both have testing programs in place to identify animal products containing antibiotic residues. For example, every tanker truck of milk is tested by the FDA for the six most widely used antibiotics and if any are detected the milk is discarded. That means all of the milk in the tanker is thrown away! Do you think farmers would be overprescribing antibiotics and risk losing the income from a full milk shipment…? No way!

The majority of large dairy farms test their milk before it even leaves the farm. The milk is then tested again by the dairy processors. For example, last year 3.5 million tanker trucks of milk were tested and only 350 were determined to contain antibiotic residues – and every single one of them was discarded.  The USDA also has personnel at processing plants who test meat determined to be at risk for antibiotics contamination. If farms are determined to be in violation they can be sanctioned.

Tanker trucks leave diary farms after inspection of antibiotic residue. The milk is tested again at the processing facility. Each tanker holds roughly 11,000 gallons of milk! Farmers are very careful to make sure there cows are antibiotic free.

However, in the very small chance that trace amounts of antibiotic remain after the withdrawal period, it is not enough to cause AMR. The amount is so insignificant, typically in parts per million or lower (1ppm would be similar to 1 second in 11.5 days); it is not enough to cause a bacterial mutation – or resistance. Basically, you are not taking a course of antibiotics or allowing germs to become resistant to antibiotics when you eat the meat on your plate.

How do AMR strains of bacteria infecting humans?

In 2013, the CDC reported that Salmonella and Campylobacter are the most common animal-borne bacteria that have evolved resistant to antibiotics and can infect humans. But how are these microbes becoming resistant? Is it from antibiotics in the waste stream? Is it through antibiotic-contaminated airborne particles? Is it from a farmer tracking manure into their kitchen? Is it from not cooking your meat to 160 degrees? Is it from over-prescription by your doctor?

Unfortunately, there is no definitive answer. There is the possibility that animal use can spawn AMR bacteria that can infect humans (and some documented cases of this happening), however, at the moment, it appears that the vast majority of AMR bacteria are from human use of antibiotics. Nonetheless, farmers, agricultural companies, allied groups, and veterinarians have decided to address this issue head on, even though they are not the primary ones responsible for the problem of AMR in human medicine.

Today’s conversation is about reducing the total amount of antibiotics used in agriculture and about banning the use of antibiotics that are important for human medicine. Remember, the concern with AMR bacteria is that the specific antibiotic becomes ineffective. However, if the antibiotic is not used in human medicine then the concern is greatly reduced.

Additionally, some food processing companies, like Cargill, have recently announced that they will eliminate 20% of the shared class medically important antibiotics used in beef cattle and they will not use any of these types of antibiotics for growth promotion. Last spring, Tyson and Perdue also announced their plans to completely eliminate the human antibiotics used in their chicken.

Bell and Evans maintains that happy chickens = healthy chickens.  Image Source

Animal producers are also asking themselves what changes they can make in the animal’s life to keep them stress-free, healthy, and strong without using antibiotics. For instance, Bell and Evans Chicken has specific practices used with their growers to have happy healthy chickens.

Bell and Evans pride themselves on never using antibiotics on their chickens, and instead use oregano to manage their chicken’s gut health and reduce disease. They believe, along with other protein producers, that a well-managed feedlot or chicken farm can eliminate or prevent the over-use of antibiotics.

Because AMR is such an important issue, new policies (specifically Guidance for Industry (GFI) #209 and #213, and a revised Veterinary Feed Directive) are changing how medically-important antimicrobial drugs are used on farms. First, all antibiotics must be authorized by a licensed veterinarian and comply with new regulations. There is a commitment by everyone in the industry to reduce the growth promotion use of antibiotics in feed and water and to allow only therapeutic use (prevention, control, or treatment of disease) of those drugs in food-producing animals.

This is a good start and more needs to be done, but should agriculture eliminate all use of antibiotics? Veterinarians and farmers will tell you no. Antibiotics are an essential tool as they are in human medicine to reduce animal suffering, prevent spread of disease, and ensure a healthy food supply.

Is Antibiotic-Free meat humane?

While most consumers are concerned about AMR, have you considered the animal welfare aspect of this issue?   What should a farmer do when they have a sick animal? What would you do if you had a sick pet or family member? Compassion and public health dictate that judicious use of antibiotics followed by the appropriate withdrawal time is the best approach.


“Antibiotic Free” means a product from animals were never treated with antibiotics.

Yet we already have a food supply almost entirely devoid of antibiotics. (Remember the withdrawal period and testing?)

Yet, consumers are still worried and want to buy antibiotic free meat, eggs, and milk. As a result, companies such as Panera Bread, McDonalds, Walmart, Costco, and Chipotle have all vowed to provide some form of “Antibiotic-Free” meat.

In addition to that, almost 40% of antibiotics used in animals are not medically important (shared between humans and animals). For example, the entire class of ionophore antibiotics, which represents about one third of the animal use, is never used in humans and is not a concern for human medicine. These are good steps for addressing what is the primary issue in this debate: making sure that front-line human antibiotics continue to be effective.

The Real Story…..

The real issue and cause of AMR is from human prescription misuse of antibiotics by doctors and patients. Now if we can only get humans to reduce their use of antibiotics. For example, in India people can buy antibiotics over the counter without a prescription – talk about a way to accelerate AMR!

According to a CDC report, antibiotics were prescribed in 68% of acute respiratory tract infections – 80% of which were unnecessary. This misuse of antibiotics promotes the evolution of resistant bacteria. It is equally impotant to take the full course of antibiotic perscribed by your doctor, even if you start feeling better right away!

The key to staying ahead of AMR is to use antibiotics wisely and appropriately. It is critically important that scientists and the pharmaceutical industry develop new classes of antibiotics and that the FDA create a regulatory policy to allow more powerful antibiotics and effective vaccines to prevent sickness in the first place. A recent study has identified an antibiotic that could prevent AMR for up to 30 years. Teixobactin has been tested successfully in mice, and human trials are set to begin in two years.

The Waste Stream

Another source of antibiotics in the environment is in the waste stream, including what an animal ‘contributes’ back to the environment. In the case of antibiotics this is mostly an issue for the animals fecal matter. For humans, many antibiotics exit the body into the toilet. Additionally, do you ever flush antibiotics down the toilet? What about the antibiotic you give to your pet? Where did that waste end up? Many antibitoics from these waste streams end up in our water!

Resistance can occur anywhere you find bacteria. AMR bacteria have even been found in the jet stream at 30,000 ft! And, if AMR can occur there, they can pretty much occur anywhere and at any time. Think about how bacteria is distributed throughout the world, including animal waste, which includes your pet, insects, birds, crops, wind, rivers, and weather. It is hard to quantify, but clearly there is a link between humans, animals, and the environment – a concept referred to as One Health by the USDA that reminds us that all are interconnected and that solutions to problems must address each component.

The Bottom Line:

Want to reduce AMR bacteria and your chance of contracting a disease? It is important to follow the CDC’s simple recommendations by washing your hands, staying up to date with vaccines, keeping your kitchen clean, and your water safe. Secondly, be wary of over prescription and misuse of antibiotics, as this is the largest factor contributing to antimicrobial resistance worldwide. Only take antibiotics when your doctor has confirmed you have a bacterial infection, and stick to the prescribed amount. Lastly, support companies that recognize that the judicious use of antibiotics results in the reduced animal suffering and improved public health outcomes. If you follow these simple rules and adequately cook your meat we will all be able to continue to consume healthy, protein rich animal protein without worries of contributing to AMR.


A special thank you to faculty in the College of Agricultural Sciences at Penn State University who provided input on aspects of this post

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