From the number and kinds of chickens we keep to the ways we choose to house and manage them, our flocks can be as individual as fingerprints. Still, whether we have just a few backyard hens or a few hundred, we all have at least one thing in common: the need to monitor and occasionally treat our chickens for parasitic worms.
Unfortunately, a single right answer or one-size-fits-all solution doesn’t necessarily exist when it comes to deworming chickens. What’s more, because poultry deworming methods and schedules vary widely, determining exactly when it’s safe to eat an egg from treated chickens can also be tricky.
Worms to Watch
Depending on factors such as their age and environment, your chickens probably already have some parasitic worms.
“An adult chicken that’s having the opportunity to graze on grass is going to pick up some [parasite] eggs,” says Megan Lighty, an avian diagnostic and outreach veterinarian and associate clinical professor at the Penn State College of Agricultural Sciences. “If I have a 1-year-old chicken that’s on pasture and there’s a few 100 or maybe even 1,000 oocysts per gram … in [a test] sample, I’m not that worried about it.”
When parasitic loads do get out of hand, your chickens’ health and egg production can suffer. Very heavy infestations can even cause death.
Among the most common worms your chickens may face? Roundworms, tapeworms, capillary worms and cecal worms, among others. Most—but not all—of these are too tiny to be seen without magnification. But, Lighty says, “There’s a few different types of tapeworms, and you might see those with the naked eye, if you’ve got a bad infestation.”
Pet or Producer?
If your birds need treatment, your options are actually somewhat limited. “I think the big thing for backyard flock owners to know that a lot of them don’t is that … [the FDA] considers all chickens to be food-producing animals, regardless of how the owner views it,” Lighty says.
“So, that really does limit my options as a veterinarian for what I can recommend. There are some drugs that—even if it’s a backyard rooster that will get a lovely burial and a headstone when it dies—there are drugs that I just cannot [prescribe] because the FDA considers that a food-producing animal.”
In other words? “There are some drugs that could be very helpful in certain circumstances for backyard chickens that are truly pets that we just can’t use,” Lighty says. “The FDA has made it very clear to veterinarians that they’re not interested in playing the game of, you know, ‘This one’s a pet and this one we might eat the eggs from.’
“It’s just a blanket [designation]. They’re all considered food-producing.”
To date, the only FDA-approved antiparasitic for use in chickens is a water-soluble preparation containing a drug called fenbendazole. Sold under the name Safe-Guard AquaSol, it can treat and control adult Ascaridia galli, a type of roundworm, in meat-type chickens and Ascaridia galli and Heterakis gallinarum, a type of cecal worm, in laying hens.
“The approved dosage regimen is 1.0 milligram/kilogram (0.454 milligram /pound) BW [bodyweight] daily orally in drinking water for five consecutive days,” says Juli Putnam, a spokesperson for the U.S. Food and Drug Administration’s Center for Veterinary Medicine.
“In chickens, no (egg or meat) withdrawal period is required when used according to labeling.”
Put another way, provided you prepare and administer the drug according to the instructions on its label, the FDA won’t require you to avoid eating (or selling) the eggs from treated chickens for a specified length of time after deworming.
Securing FDA-approval for a drug that will be used in food-producing animals doesn’t necessarily come quickly or easily, since human safety comes into play. “To show that the food products are safe, a drug sponsor usually conducts what are called human food safety studies,” Putnam says.
These studies typically include evaluations of toxicology, residue chemistry and microbial food safety. A study’s data-gathering and measurement methods are also analyzed.
“By looking at detailed information about the drug in laboratory animals, toxicologists at [the FDA’s Center for Veterinary Medicine] determine the ‘acceptable daily intake’ or ADI,” Putnam says. “The ADI is the largest amount of the drug in a person’s diet that is not harmful even if he or she consumes that amount every day.”
As for evaluation of chemical residues, chemists examine how the drug being evaluated makes its way through the treated animal. That includes how the animal’s system breaks down and eliminates the drug.
“Based on this information, along with the [acceptable daily intake], the residue chemists set the tolerance for the drug in the edible tissues of treated animals,” Putnam says. “The tolerance is the highest level of drug residues that are legally allowed to be in or on food products made from treated animals.”
Chemists then use the established tolerance values to determine the withdrawal period for the drug being evaluated. “The withdrawal period allows for drug residues in the edible tissues of the treated animal to get to levels that are at or below the tolerance,” Putnam says. “If the withdrawal period is followed, the amount of residues in the food products made from the treated animal will be below the tolerance and are safe to enter the food supply.”
When evaluating drugs for approval, the FDA Center for Veterinary Medicine’s microbiologists also consider the likelihood that, with continual exposure to the same drug, parasites and pathogens could become resistant to it. (If that were to happen, the drug might become a less effective remedy for your flock.)
Furthermore, “The microbiologists look at the impact of that resistance on public health, and if the impact is potentially negative, they determine if the risk is acceptable,” Putnam says.
Fenbendazole may be the only antiparasitic drug currently approved for deworming meat- and egg-type chickens. However, it isn’t the only drug that can eliminate various parasitic worms from chickens. Drugs such as praziquantel, oxfendazole and levamisole are a few effective antiparasitics, but they haven’t gone through human food safety evaluations relative to their use in meat- and egg-type chickens.
“Because praziquantel, oxfendazole and levamisole aren’t approved for use in poultry, the FDA doesn’t have the appropriate residue data to determine whether eggs treated with these drugs would be ‘safe’ to eat,” Putnam says. “Any treatment of chickens with these drugs would be considered extra-label use.”
(Also known as “off-label” use, extra-label use refers to a deviation from the FDA-approved use spelled out in the drug’s labeling documentation.)
“Since chickens are food-producing animals, extra-label use of drugs can only be done under a veterinary-client-patient relationship with a prescription from a veterinarian,” Lighty says. “It would have to be handled on a case-by-case basis with a veterinarian who has a relationship with the client and the patient, and any [egg] withdrawal times have to be determined on a case-by-case basis.”
So, what if you were to engage in extra-label use of a prescription drug and your chickens’ eggs included residues from that drug? “Any amount of residues from extra-label use would be illegal,” Putnam says.
Because the water-soluble preparation of fenbendazole is intended for use on commercial chickens, it can be an expensive deworming choice for hobbyists. “The smallest bottle you can buy is a liter, and it’s a couple hundred dollars,” Lighty says. “Your average backyard chicken flock is going to need a few milliliters of it.”
To save money, some poultry-keepers purchase fenbendazole-containing products, which are actually intended for use in cattle or sheep instead, but they aren’t necessarily getting what they pay for. “[Those products] are cheaper, but they are formulated differently,” Lighty says. “They are intended to be bolused—basically force-fed to the cow at the correct dosage—whereas Safe-Guard AquaSol is actually designed to be mixed in with the drinking water, which makes administration easy.”
“If you try to take one of the products that’s formulated for cattle or other livestock and put it in the drinking water, it falls out of solution,” Lighty says. That means there’s no guarantee that your flock will be able to take up the medication that it needs. There’s also no good way to monitor the dose your chickens might get.
“Technically, if somebody wanted to use the cattle formula, you’re using an over-the-counter product extra-label,” Lighty says. “You should have a prescription from a veterinarian, but there’s nothing that stops you from walking into the farm-supply store and buying that.”
That could be true of other antiparasitic drugs not labeled for use in chickens. That said, however, in the absence of food safety evaluations and without veterinary assistance, you could be jeopardizing your hens’ health—not to mention your own.
The Best Medicine
Aside from which deworming medication to use, deciding when to use one on chickens can also be confounding. “I know there are some recommendations out there that say, ‘You should deworm a backyard flock … every so many months,’” Lighty says. “I personally don’t think that’s necessary for most flocks.
“There are some backyard flocks that can get away with never deworming. It really just depends on the number of birds you have and in how large or small of a space are they, and do you have multiple species and multiple ages on the farm that might affect the [parasitic] burden?”
Rather than automatically medicating your chickens as a preventative measure, Lighty recommends having fecal floatation testing done by a local veterinarian or via your state diagnostic lab or similar agency. “It’s the same procedure that people would do with their dog or cat when they go to the vet … to see what the [parasite] burden is and then decide, ‘Do I need to treat?’” she says.
With those test results in hand, you’ll have a better idea about your chickens’ parasitic loads, the types of parasites involved, and whether—and how—you should medicate your flock.
If you want to help mitigate the need for antiparasitic medications altogether, you can do a couple of things. You can disrupt the life cycles of some common parasitic worms by keeping all chicken runs and coops as clean and dry as you can and, if possible, by periodically rotating your chickens’ grazing locations.
Until recently, poultry-keepers also had over-the-counter access to the antiparasitic drug piperazine, marketed as Wazine. But the product’s manufacturer voluntarily withdrew its application for FDA approval in 2020, and it’s no longer on store shelves.
Also worth noting, a host of other over-the-counter deworming remedies for chickens are available containing everything from garlic extracts and herbal compounds to diatomaceous earth. The good news is that these more natural preparations aren’t likely to contribute potentially harmful residues to your chickens’ eggs or meat. On the other hand, their respective degrees of effectiveness may vary widely.
This article originally appeared in the July/August 2023 issue of Chickens magazine.