Hi stranger! Signing up for MypetMD is easy, free and puts the most relevant content at your fingertips.

Get Instant Access To

  • 24/7 alerts for pet-related recalls

  • Your own library of articles, blogs, and favorite pet names

  • Tools designed to keep your pets happy and healthy

or Connect with Facebook

By joining petMD, you agree to the Privacy Policy.

petMD Blogs

Written by leading veterinarians to provide you with the information you need to care for your pets.

The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

The Argument over Antibiotics

As a medical professional, I use antibiotics. In fact, I use them every day. I prescribe them to horses, beef and dairy cattle, sheep, goats, pigs, llamas and alpacas. These drugs have fun names like Tetradure and Nuflor and Spectramast. Most are injectable, but some are pills that are fed or put down the throat of an unwilling bovine with a tool called a "balling gun."  A common horse antibiotic is usually given orally as a powder — hidden sneakily in some molasses for those crafty and oh-so-suspicious equines. And then there’s the old, comfortable standby: penicillin.


Lots of people blame agricultural use on the growth of antibiotic resistance, but the over-prescription and over-use of antibiotics on the human side is also to blame. No one in this argument is innocent, but there is a lot of finger pointing, with no one wanting to take responsibility as to who, exactly, is causing all this antibiotic resistance. The fact is we all are.


Here are some facts. In agriculture, certain antibiotics can be fed to livestock for what is called "production purposes." Some time ago, people began to see that livestock that were given antibiotics at a low level would gain weight faster than animals not given these same antibiotics. Now there are livestock feeds manufactured with low (also called subtherapeutic) levels of antibiotics for use in beef cattle, swine and poultry to aid in weight gain. This has been going on for decades and is a large part of the livestock industry in this country.


In 1987 the Institute of Medicine conducted a review of the human health risks associated with the subtherapeutic use of penicillin and tetracycline in animal feed. Although this committee only looked at data from Salmonella infections that resulted in human death, the committee could not find direct evidence that subtherapeutic use of penicillin or tetracycline in animal feed posed a human health hazard.


In contrast, in 1997 the World Health Organization (WHO) gathered a panel of experts to re-examine this question and concluded that all uses of antimicrobials lead to the selection of resistant forms of bacteria.


Since then, there have been hundreds, if not thousands of other studies and reviews and committees held to examine this problem. Some conclude that subtherapeutic levels definitely cause an increase in resistance; others say there is no direct substantial evidence.


Members of the public and media outlets seem to pick and choose whichever studies fit their needs. I’m not trying to be negative here, just as honest as I can be with the knowledge I have. To me, it seems like everyone is to blame.


I do not work at feed yards and do not prescribe feed that contains antibiotics for productive claims. These feeds can only be bought under something called veterinary feed directives (VFDs), so there is at least some sort of veterinary oversight in administration of these feeds, however minimal. Additionally, there are plenty of antibiotics that are allowed nowhere near food animals for two good reasons:

  1. It causes harmful residues in edible tissues that can make it into the food chain.
  2. We want to protect a handful of antibiotics for human use only.


As such, this is a sticky place for us food animal vets to reside. On the one hand, yes, antibiotic resistance scares me and I know it’s a real problem. On the other hand, how do you tell a farmer making his living that he can’t use feed with tetracycline in it anymore when it helps his animals to gain weight, which increases his profit margin, therefore putting food on his table?


The best thing I can do is try to explain to people that it’s not just the beef industry, or the poultry industry, or the whomever-you-want-to-pick-a-fight-with industry that’s the only problem. We all have a stake in this, so we all must take responsibility. Don’t take antibiotics just because you have the sniffles, and I won’t prescribe antibiotics to a goat just because he "doesn’t seem right." You do your part and I’ll do mine and we’ll wait to see what happens next.



Dr. Anna O’Brien



Image: branislavpudar / via Shutterstock

Comments  6

Leave Comment
  • Humans
    06/15/2012 11:18am

    I've long been of the opinion that much of the problem is overprescribing of antibiotics to humans. Got a cold? Get antibiotics.

    Even with all of the resistant-strain news, I know people that still insist their doctor give them antibiotics for a virus. If they going to insist on something, perhaps they should insist on antivirals. :-)

    For some reason, humans cannot fathom that there's nothing to help the common cold except to relieve symptoms.

    The question that comes to mind this morning, though, is if a cow/steer/bull has been treated with penicillin and is now in the food chain, is there any risk to a human with a penicillin allergy? Seems like we would have heard something about that if it's true.

  • How does that work?
    06/15/2012 01:29pm

    What is the mechanism by which antibiotics make livestock gain weight quicker?

  • Problem Solved
    06/15/2012 07:53pm

    I can't muster up any sympathy for Farmer Feed. I don't view the suffering and slaughter of animals as responsible stewardship.

    I took personal responsibility in 1969--when I quit eating meat. That decision was an instantaneous one, made on the day (in '69) when I was given an (unplanned) guided tour at a slaughter house.

    "Grab the bull by the horns": stop eating meat....That solves that problem.

  • Part 1
    06/16/2012 01:40pm

    Kid-kick-start: Problem solved? I don’t think so. Have you also quit using anti-bacterial soap and eschewing the personal use of antibiotics? Or in your pets? (A good chunk of doxycycline passes through a dog unchanged and comes out in the feces as active.)
    THIS is the overriding issue concerning antibiotic abuse – the contamination of our water supply with antibiotic resistant bacteria – both salt and fresh water:

    “Large quantities of antibiotic-resistant bacteria enter the environment via municipal -- and especially hospital -- wastewater streams. “
    “In the sewage-laced sediment of the Tijuana River Valley, Cummings and his students have uncovered an array of genes that help their bacteria hosts survive.”

    Yes, runoff from feed lots is also a big issue as far as local waters. And a local problem doesn’t stay local for long because wild critters pick up the bacteria from the water and spread them wherever they go:

    Even open-air poultry trucks spread resistant bacteria:

    Not to mention flies:

    Another wrinkle in the equation – heavy metal pollution:
    “Our results imply that heavy metal pollution may contribute to increased antibiotic resistance through indirect selection.”

    So once those resistant bacteria are out there, there is no way to control where they end up. Bacteria exchange genes and the effect can multiply without any further assistance from humans. The bottom line is, wherever antibiotics are used, there will be a tendency to foster resistance to those antibiotics.

    A way out? Organic poultry production can knock out resistant bacteria in just one flock after transition:

    And Dr. O’Brien , I have to say those studies are wrong wrong wrong. Take a gander at this:

    And don’t worry about telling farmers they can’t use antibiotics, the FDA is starting, at least, to address the issue, however much they’re soft pedaling it.

    Barbcci: I don’t know the exact mechanism of weight gain due to subtherapeutic antibiotics. I would suspect it has a lot to do with overcrowding and stress fostering disease, but this paper on poultry sez otherwise. Though chickens can get coccidiosis, which can cause a whole flock to die.

  • Part 2
    06/16/2012 01:40pm

    Like it or not, the best way to stop some of this is to demand McDonald’s, Taco Bell and others serve up chicken and beef raised w/o antibiotics. So perhaps it’s all those meat eating people who can help improve the situation.

    Oh and quit demanding, accepting antibiotics for any old illness. And load up on probiotics after a course of antibiotics (if they were really necessary). And it’s not just a meat issue, but sanitation in the fields where veges are picked, or better health care for farm workers.

  • 06/16/2012 04:51pm


    Okay, point taken, so, correction: big chunk of the problem solved. Once again, my recommendation: don't eat meat.

    Ah, yeah, my yellow lab will probably require an antibiotic at some time, but that's what antibiotics are for: truly ill people and animals. That's not misuse. Feeding livestock antibiotics merely to fatten them up is misuse/overuse.

    And no, I don't use anti-bacterial soap.

Meet The Vets