When, Why and How to Deworm Chickens
Most chickens have worms of one sort or another, and an otherwise healthy chicken can tolerate a modest worm load. A heavy worm load, however, can impair a chicken’s immune system, making the bird more susceptible to diseases. Likewise, illness or other stress impairs the chicken’s immune system, making the bird more susceptible to a heavy worm load. Here’s what you need to know about worms that can potentially parasitize your chickens and how to keep them at bay.
The Nature of Worms
A worm infestation differs from an infection caused by bacteria, fungi, protozoa, or viruses, in that worms do not multiply inside a chicken’s body. Rather, a worm’s eggs or larvae are expelled in chicken poop. A chicken gets a worm by eating a worm egg or larva shed by a wormy chicken (or other bird), which then matures within the chicken. How serious a chicken’s worm load is, therefore, depends on how many infective eggs or larvae the chicken eats.
Most chickens have worms somewhere in their bodies. Under good management, the worms and chickens become balanced in peaceful coexistence, with the chickens showing few, if any, signs of having worms. A worm load becomes a problem, however, if the chickens become stressed in other ways, and especially if they have roamed in the same yard, picking in the same soil year after year.
Compared to other diseases, worm infections develop gradually and therefore tend to be chronic. A chicken infected with intestinal worms may gradually lose weight as the worms interfere with food absorption and other digestive processes. Worms that invade the respiratory system cause gradually worsening breathing difficulties and eventually block the airways. Less commonly, worms invade other parts of the body. In most cases, a severe infestation left untreated, can result in a chicken’s death.
Rounds and Flats
Based on their general body shapes, parasitic worms are organized into two main groups — roundworms and flatworms. Roundworms are thin, thread-like worms also called nematodes, from the Greek words nema, meaning thread, and odes, meaning like. Flatworms have flattened bodies that are more ribbon-like than tubular. The flatworms that most commonly invade chickens are cestodes, from the Greek word kestos, meaning belt. Most of us know them as tapeworms.
In the number of species involved and the damage they do, roundworms are a more significant threat to chickens than are tapeworms. Different roundworm species invade different parts of a chicken’s body, including the eye, windpipe, crop, stomach, gizzard, intestine, and ceca. (Eye worm was discussed in detail in the December/January 2013-14 issue of Backyard Poultry.)
By far the most common parasitic worm in North American chickens is the cecal worm (Heterakis gallinae). As its name implies, it invades a bird’s ceca — two finger-shaped pouches at the juncture of the small and large intestines, where fermentation breaks down coarse cellulose. Other than carrying blackhead, to which chickens are typically resistant, the cecal worm rarely affects a chicken’s health.
Another common internal parasite is the large roundworm (Ascaridia galli). It is approximately the thickness of pencil lead and can grow as long as 4.5 inches — big enough for us to see without a magnifying glass. Mature large roundworms roam a chicken’s small intestine. Occasionally one will migrate down the intestine to the cloaca, and from there, up the oviduct, getting trapped inside an egg — a decidedly unappetizing occurrence.
Signs of an overload of large roundworms include pale head, droopiness, weight loss (or slow growth in young birds), emaciation, and diarrhea with increased white urates (the chicken equivalent of pee). In a severe infection, the intestines can plug up with worms, causing death. Even a somewhat mild infection may be devastating in the presence of some other disease, such coccidiosis or infectious bronchitis.
The only approved remedy for large roundworms is piperazine, which has been used for so many years that the worms are becoming resistant to it. Therefore more effective (but not approved) drugs are often used for backyard flocks, particularly exhibition birds and others types not kept for meat or table eggs.
Many other less common roundworms affect chickens. One is gapeworm (Syngamus trachea), which causes a relatively uncommon respiratory condition called the gapes. Another is the capillary worm (Capillaria spp.) — also known as threadworm because of its thin threadlike appearance — which can cause emaciation and a decline in egg laying.
Tapeworm is common in backyard chickens. Like roundworms, tapeworms come in many species, most of which are host specific — those infecting chickens invade only chickens and their close relatives. Tapeworms have suckers on their heads, which they use to attach themselves to the chicken’s intestine wall. Each tapeworm species prefers a different part of the intestine.
A tapeworm’s body is made up of individual segments, each of which has both male and female reproductive organs. As the segments farthest from the head mature, they become wider and fill with eggs until they break away and are passed in chicken poop. You might see segments, each containing hundreds of eggs, in droppings or clinging to the chicken’s vent area.
A general sign of tapeworm infection in young chickens is stunted growth. Signs in mature chickens include weight loss, decreased laying, rapid breathing, and dry, ruffled feathers. Tapeworm infections are difficult to treat, and many common dewormers have no effect at all. The benzimidazoles are typically used to treat backyard chickens for tapeworm.
It bears repeating that a chicken in a healthy environment becomes resistant to worms as it matures, therefore the best way to prevent worm overloads is the keep your chickens healthy. Good management that provides a healthful environment is far superior to attempting to control parasitic worms through constant medication.
Unless you take measures to minimize or eliminate sources of infection, deworming becomes an expensive and never-ending cycle. Not only that, eventually, worms become resistant to the chemical dewormers and you end up dealing with superworms. Good management to provide a healthful environment includes these sensible parasite control measures:
• provide a proper diet that includes vitamin A, the B-complex vitamins and animal protein;
• thoroughly clean feeders and drinkers often;
• practice good housing sanitation, including regular bedding management;
• avoid mixing chickens of different ages from different sources;
• do not overcrowd your birds, which can rapidly lead to a worm overload;
• minimize situations that chickens find stressful;
• control alternate hosts (see “Life Cycles of Worms that Parasitize Chickens” on page 49);
• provide a well-drained and puddle-free yard; and
• periodically rotate the yard and mow or till the resting yard.
Parasitic worm eggs and larvae dry out fairly rapidly when exposed to air and sunlight. Rotating the chickens’ run and mowing the vegetation or tilling the soil of the previous run exposes expelled mature worms, larvae, and eggs to sunlight, helping reduce the overall population.
In a rainy climate, or where rainfall is higher than usual, worm eggs and larvae in the environment are protected from drying out by moisture and mud, allowing more to survive and increasing the potential for worm overloads in chickens. Compared to a dry climate, more aggressive parasite control and de-worming measures are therefore needed in a wet climate.
Natural Worm Control
Effective natural methods of worm control generally work by making the environment inside the chicken unpleasant for parasites. They are therefore more suited to preventing worms than to eliminating existing worms. A number of homeopathic and herbal preparations are available on the market that offers varying degrees of effectiveness.
Unfortunately, no definitive studies have been made on any of the natural control methods to determine such things as their efficacy, the amount required, or duration of treatment. Further, the concentration of active ingredients within plants can vary, causing variable efficacy. And, just because chickens are treated with a certain natural remedy and don’t have worms doesn’t necessarily mean the remedy pre-vented worms. Those chickens may not have had worms even without the remedy.
On the other hand, many of the natural remedies provide some nutritional benefit, which can improve a chicken’s overall health and therefore boost its immunity to parasitic worms. Here are some of the more popular natural methods:
BRASSICAS, when fed raw, contain a sulfurous organic compound that is responsible for their pungent taste and supposedly repels internal parasites. Brassicas include cabbage (as well as broccoli and cauliflower leaves), horseradish, mustard, nasturtiums, radishes, and turnips.
CUCURBITS— including cucumbers, pumpkins, and squash — contain the amino acid cucurbitine in their raw seeds that is marginally effective against tapeworms by causing reproductive degeneration. Many sources suggest grinding or chopping the seeds, which is unnecessary except maybe for really huge pumpkin and squash seeds, which could be given a quick whirl in a blender. Otherwise, just cut the fresh cucurbit in half and let the chickens do the rest.
GARLIC supposedly prevents the eggs of some parasite worms from developing into larvae. As a method of worm control, garlic is added to drinking water at the rate of four crushed cloves per gallon. However, chickens that aren’t used to garlic may not drink the flavored water. Further, the excessive use of garlic can be hazardous to a chicken’s health. Although garlic is beneficial to good gut bacteria, too much can interfere with gut health. Excessive garlic can also damage red blood cells, causing anemia.
WORMWOOD, of which there are many species, gets its name from its parasitic worm controlling properties. Some species grow wild, while others are garden herbs. The active ingredient in wormwood is the oily organic compound thujone, which is a neurotoxin — a poison that affects the nervous system, causing muscle spasms. Used regularly, or in excessive amounts, it can cause convulsions and death, not just to the parasitic worms but also to the chicken. A relatively safe way to use wormwood is to grow it at the edge of the chicken yard and let the birds regulate their own intake. Other herbs that contain thujone include oregano, sage, tansy, tarragon, and their essential oils.
DIATOMACEOUS EARTH (DE) is popularly fed to chickens as a dewormer on the theory that it dehydrates internal parasites the same way it dehydrates external poultry parasites and garden insects. But think about it: if DE worked the same on internal worms as it does on garden insects, it would do likewise to a chicken’s innards. Although many chicken keepers swear by it, no one has been able to explain how or why it works. It’s possible that the large number of trace minerals contained in DE help boost a chicken’s immunity. It’s equally possible that people who treat their chickens with DE ensure their birds’ health in other ways.
Do not rely on any natural means of controlling parasitic worms if your chickens are already suffering from a heavy worm load, especially if you expect your birds to live into old age. When worms get out of control and reach the point where they affect the chicken’s health — causing your birds to look scrawny and scruffy, lose weight, and lay few eggs — you may have no choice but to use a chemical dewormer.
The only FDA-approved dewormers for chickens are hygromycin-B and piperazine. Many others are commonly used by backyard poultry keepers but are illegal for use in a flock raised for the sale of eggs or meat. If you consistently use one chemical dewormer, parasites will become resistant to it, which generally takes between eight and 10 generations. To minimize the development of resistant strains, avoid using the same dewormer year after year. All the dewormers in the same chemical class work the same way, so to avoid resistance rotate chemical classes, not just brand names.
HYGROMYCIN-B (trade names Hygromix 8, Rooster Booster Multi-Wormer) is sold as a multi-purpose dewormer for con-trolling capillary worms, cecal worms, and large roundworms. It kills mature worms, reduces the ability of female worms to lay eggs, kills some larvae, and renders surviving larvae unable to reproduce when they mature. Hygromycin requires no egg discard period, but a three-day withdrawal time for meat birds. However, unlike other chemical dewormers, hygromycin is an antibiotic, which should concern anyone who worries about the indiscriminate use of antibiotics.
PIPERAZINE (trade name Wazine) is effective only against large roundworms. It acts as a narcotic, weakening and paralyzing mature worms and causing them to be expelled from the chicken, live, with a bird’s digestive wastes. Piperazine affects only adult worms, but not developing worms that are attached to the chicken’s intestinal lining. Treatment must therefore be repeated in seven to 10 days, giving young worms time to release their hold on the intestinal lining when they mature. Piperazine is not approved for hens laying table eggs. The withdrawal period for meat birds is 14 days.
IVERMECTIN (trade name Ivomec) is a systemic livestock dewormer in the class of drugs known as avermectins. It is effective against most roundworms, but not tapeworms, and can be toxic to chickens in relatively small amounts. It works by paralyzing worms, which are then released in the chicken’s poop. Most farm stores sell ivermectin as a cattle dewormer in one of three liquid forms: injectable, drench (administered by mouth), and pour-on. The injectable and drench forms may be given to individual chickens by mouth or added to drinking water. The pour-on form must be applied as drops to the skin at the back of the neck. Repeat in 14 days. Since none of the formulations is sold specifically for poultry, no withdrawal period has been officially published; unofficially, the withdrawal time is 21 days.
EPRINOMECTIN (trade name Ivomec Eprinex) is another avermectin that is effective against most roundworms, but not tapeworms. It is applied to the skin at the back of a chicken’s neck twice a year. It is marketed primarily for dairy cows, for which no milk withdrawal period is required.
SELAMECTIN (trade names Revolution, Stronghold) is also an avermectin, sold primarily for deworming cats and dogs. In the United States, it requires a prescription but may be purchased from other countries online. It is applied to the back of a chicken’s neck.
ALBENDAZOLE (trade name Valbazen) is in a class of drugs known as benzimidazoles, which kill worms by disrupting their energy metabolism, and — unlike most other dewormers — are effective against tapeworms as well as round-worms. One treatment, given by mouth, is generally enough to kill any type of worm, but to be sure, repeat the treatment in two weeks.
FENBENDAZOLE (brand names Panacur, Safe-Guard) is another benzimidazole that is effective against most worm species. It comes as a powder (added to feed), liquid (added to drinking water), or a paste (placed inside the beak). Treatment is repeated in 10 days. Fenbendazole is approved for turkeys, for which no withdrawal period is required. It is not approved for chickens, and if overused can be toxic. Deworming with fenbendazole during the molt can deform newly emerging feathers, and deworming breeder cocks may reduce sperm quality.
LEVAMISOLE (trade name Prohibit) is in a class of drugs known as imidazothiazoles. It is effective against most roundworms, paralyzing the worms and causing them to be expelled, live, with digestive wastes. The drench form is added to drinking water; the injectable form is injected under the skin. It should not be used on seriously debilitated chickens, because it can decrease the bird’s ability to fight infection.
All dewormers are transported throughout the chicken’s body, metabolized, and eventually excreted. But different dewormers require different amounts of time before they disappear entirely from a bird’s body. Any drug approved for use in poultry has an established withdrawal period — the amount of time required before the drug no longer shows up in the bird’s meat or eggs.
The withdrawal period for the only dewormer approved for meat birds, piperazine, is 14 days. No dewormer is approved for table egg production, because the development of each egg, starting with maturing of the yolk in the ovary, occurs over such a long period of time that few studies have been done to establish exactly how many eggs must be laid before drugs no longer appear in the eggs.
Although most of the worm species that affect chickens do not infect people, most of the chemical dewormers used on chickens and other livestock are also used to rid people of the types of worms humans do get. An occasional inadvertent deworming probably wouldn’t hurt most of us, but over time potentially serious problems can arise.
Piperazine, for example, is used to treat humans for roundworms and pinworms. Residual piperazine in meat or eggs could result in resistant roundworms and pinworms in humans who regularly eat such meat or eggs. (Where the humans get infected with worms is another issue; people don’t get the parasites from their chickens.)
A second problem occurs in someone who is allergic to the drug in question. Again using piperazine as an example, anyone allergic to the solvent ethylene-diamine may experience an allergic reaction to piperazine residue in meat or eggs.
A third issue is that a dewormer may interact with certain prescription medications. Such an interaction could increase the risk of side effects or cause some medical problems to become worse.
Online discussions about deworm-ing chickens often include specific withdrawal times for various products that are not approved for poultry in the United States. Some of these withdrawal times are the result of guesswork or misinformation; others are established in countries where the drug in question is approved for use in poultry. Unfortunately, people who post this information don’t always tell you what country they’re in or where they obtain their information. If you use a product off-label on chickens raised for your own use, an egg discard time or meat bird withdrawal period of 14 days would not be unreasonable, and 30 days would be even better.
How often your chickens need de-worming, if they need it at all, depends in large part on the way your flock is managed. Chickens who are kept into old-age in the same coop and yard year after year are more likely to need more frequent deworming than a flock that enjoys yard rotation or is periodically replaced by younger birds following a complete coop clean-up. Similarly, thoroughly cleaning out the coop and replacing old litter after a deworming treatment reduces the speed of reinfestation.
A flock living in a warm, humid climate, where alternate hosts are prevalent year-round, requires more aggressive deworming than a flock in a cold climate, where alternate hosts are dormant part of the year. The only way to determine your flock’s worm load, and therefore how often deworming is needed, is to have regular fecal exams done by a veterinarian, which will increase your peace of mind as well as likely cost less than the unnecessary purchase of deworming products.
Life Cycles of Worms That Parasitize Chickens
The life cycles of parasitic worms involve three basic stages: adult, egg, and larva. For worm species that mature and sexually reproduce inside a chicken’s body, the chicken is considered to be the natural host. But chickens are not the only natural hosts for most worm species that affect backyard flocks. The large roundworm, or ascarid, for example, also infects turkeys, ducks, and geese.
Once a worm matures inside the chicken’s body, it produces either eggs or larvae, which are expelled in the chicken’s poop. Depending on the worm’s species, the eggs or larvae may infect new chickens either directly or indirectly. Eggs or larvae that are expelled by one chicken, then are ingested by and infect another (or the same) chicken, have a direct life cycle.
Some worm species require an additional step: The larvae must be eaten by some other creature — such as a beetle or an earthworm — and then that creature (worm larvae and all) is eaten by a chicken. The intervening creature, in which a worm lives during an immature stage in its life cycle, is considered to be an intermediate or alternate host. Parasitic worm species requiring an alternate host have an indirect life cycle.
More than half the roundworms and all tapeworms that invade chickens require an alternate host. Knowing which parasites have indirect life cycles, and which alternate hosts they involve, is an important part of your parasite control program. Indirect-cycle parasites involving earthworms, for instance, tend to be a greater problem in spring, when frequent rain brings earthworms to the soil’s surface. Other indirect-cycle parasites may create greater problems in late summer, when beetles, grasshoppers and similar alternate hosts proliferate.
Direct cycle worms and those requiring indoor-living alternate hosts (such as cockroaches or beetles) are more of a problem in penned birds. Indirect-cycle worms requiring an outdoor-living alternate host (such as grasshoppers and earthworms) are more of a problem in pastured flocks.
All tapeworms require an alternate host — which may be an ant, beetle, earthworm, fly, slug, snail, or termite — that eats either individual worm eggs or a whole segment and in turn is eaten by a chicken. Caged chickens are most likely to be infected by flies as alternate hosts. Litter-raised flocks are likely to be infected by beetles. Pastured chickens are more likely to be infected via ants, earthworms, slugs, or snails.
Since most worms spend part of their life cycles off the bird’s body, a good parasite prevention program involves controlling alternate hosts around the coop. Take care when using insecticides, though, since chickens can be poisoned from eating poisoned insects. To minimize the spread of direct cycle parasites, either design housing so chickens can’t pick in droppings that accumulate under roosts, or frequently clean out the droppings.
Parasitic Worms & Their Alternate Hosts
CAPILLARY WORM : None (direct cycle) or earthworm
CECAL WORM : None or beetle, earwig, grasshopper
GAPEWORM : None or earthworm, slug, snail
LARGE ROUNDWORM : None
TAPEWORM : Ant, beetle, earthworm, slug, snail, termite
Gail Damerow is author of The Chicken Health Handbook which, along with her several other books on raising chickens, is available from our bookstore.