Why Free-Range Hens Might be Less Susceptible to Salmonella than Their Factory-Farmed Sisters: Results from the Great Egg Challenge of 2010

No Salmonella in my eggs

No Salmonella in my eggs.

I'll vouch for that.
Yum, yum. I’ll vouch for that.







The results are in.

Earlier this month I speculated that the root cause of the recent foodborne epidemics like the Salmonella outbreak was to be found in the very nature of large-scale, industrialized agriculture: vast cacophonous barracks reeking of fumes from ammonia and housing 50,000 to 125,000 caged hens, debeaked to prevent them from pecking each other to death then packed into “battery” cages so tightly that they can’t turn around or flap their wings.

From an admittedly unscientific point of view, I considered my own backyard hens. As they peck and scratch through their daily routine, they encounter rodents, wild birds, manure, and cats, all cited by the Food and Drug Administration as examples of the filthy conditions under which the Iowa-based Wright County Egg chickens responsible for outbreak lived. Yet my birds have never sickened anyone.

A reader suggested that I should get my eggs tested. “You might be surprised at the strains of salmonella they contain,” he wrote. I accepted the challenge. The lab tests came back last week. No Salmonella.

Which left me relieved, but puzzled. Why could my 12 hens be constantly exposed to the same sanitary evils as the 7 million Wright County battery chickens, and still lay salmonella-free eggs? Does raising chickens under free-range conditions make them less susceptible to Salmonella?

My reader suggested that perhaps the care I took in handling my eggs—cleaning their shells and cooking them to high enough temperatures to kill Salmonella—was the reason there have been no problems. As much as I’d like to say that’s true, I don’t necessarily scrub the shells of my eggs, and I’m a confirmed sunny-side-up man; my partner likes hers soft-boiled.

Some background: Salmonella enteritidis, the strain currently sickening Americans, lives in chickens’ intestines. Sometimes it migrates to their uteruses. Eggs can become contaminated either on the outside of their shells through contact with feces, or internally before they are laid. (Here’s a good description of how the bacteria get in eggs.)

One explanation for why my eggs were Salmonella-free might have been that the odds to begin with were highly in my favor. Even in areas of high contamination, only one egg in 10,000 will become infected because infected hens shed the bacteria intermittently, according to Patrick McDonough, a bacteriologist at Cornell University’s veterinary school. McDonough added that my chickens probably arrived at my coop from the hatchery as healthy chicks and had never been exposed to the bacteria.

 Another reason might be that raising chickens under a free-range system makes them less susceptible to salmonella. “I don’t think there is any doubt about it that healthy chickens living in decent surroundings are just going to be a lot more resistant to salmonella,” said John L. Ingraham, emeritus professor of microbiology at the University of California Davis, and author of the book March of the Microbes, recently published by Harvard University Press. “Take any creature, ourselves included, you put them in a terrible stressful conditions and they become susceptible to disease.”

Ingraham, who happens to maintain 13 laying hens, also suspects that the massive doses of antibiotics fed to confined farm animals could be a factor in the spread of Salmonella. “Antibiotics kill off healthy, normal intestinal flora. That gives salmonella a good chance to get started there,” he said.

Recent studies of hens in France and Great Britain confirm that birds that are allowed to roam are less likely to get salmonella than those kept in confinement.

Ingraham has no qualms about making traditional Caesar salad dressing and mayonnaise—both of which involve uncooked eggs—with eggs from his own flock. “I’d be afraid to do that with a supermarket egg,” he said.

Me, too.

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  1. Joanne Rigutto says:

    Excuse me, but what specific antibiotics are allowed to be fed to hens while laying? I have livestock and poultry both. All of the antibiotics, coccidiostats, etc. I’ve ever come across are either flat out not approved for use in food/food producing animals, or have withdrawl times for milk, meat or egg production.

    If any of these are used the bird’s eggs can’t be used for human consumption.

  2. Joanne Rigutto says:

    Here’s a list of drugs approved for use in chickens and their withdrawl times. Note that all but perhaps 1 drug are prohibited from use in hens actively laying eggs for human consumption.


  3. Barry says:

    Thanks Joanne. I think Ingraham meant that if a hen received antibiotics at any stage of its life, it would destroy “good” microbes in its gut, making it easier for Salmonella to get started.

  4. Joanne Rigutto says:

    You’re welcome Barry. I think it depends on the type of antibiotic and the duration of treatment. For instance, if I were to keep a pullet on antibiotics it’s whole youth untill it lays, especially if it’s on a broad spectrum antibiotic, then I could see where there could be problems, especially when the bird is introduced to the cage environment, stress rises, etc. all of which can impact the functioning of the immune system. Especially with white leghorns, a very energetic, curious and pushy breed of chicken. They are the most ‘foreward’ birds I’ve ever worked with. Once a white leghorn decides she’s going to go somewhere or do something, she’s going to do it or go there. You can try to stop her, but I never bet on the human being the winner in the contest. The birds are relentless and will wear you down like a river wears a granite boulder down…..

    On the other hand, while I don’t know what specific types of drugs a commercial cage layer facility might have their pullets on prior to laying, I do know the drugs available to me through our local feed stores. I have a small farm in Mulino, Oregon and keep free range hens to provide eggs to my CSA members and my family. The main drug I’m used to seeing in poultry feed is Amprolium, which is a coccidiostat. Coccidia is a protazoan parasite that’s endemic to just about everywhere. When I bring new pullets in as either day olds or home hatched chicks, I usually put them on a medicated crumble with amprolium for the first few weeks. I’ve raised chicks, turkey poults and upland game birds on medicated and on unmedicated, feeds. I consider the amprolium early on as cheap insurance, especially if I bring in several hundred dollars worth of new stock as I did this year. I just can’t afford to loose $200 worth of new livestock to a disease outbreak. Once the birds are older and have a developed immune system, I pull them off.

    On the other hand, I have some hens who are just bound and determined to be mommas and sneak off, set a nest and then turn up with their kids in tow. I haven’t noticed any difference in performance, feed converstion, growth, etc. in my laying birds or in the medicated vs unmedicated youngstock after they are a couple months old. I’d think that if the birds didn’t have benificial bacteria in their guts they’d have a hard time digesting their feed and combatting infections, etc.

    Perhaps it’s because I only use amprolium and that for only the first few weeks of the birds’ lives and amprolium maybe doesn’t do in the good bacteria like a broad spectrum antibiotic like penecillin would?

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