Fecal Examination in Backyard Chickens 101-Part III

Continued from Part II

Part III. Under the Microscope

Arguably the most difficult part of this whole process is understanding what you are seeing through the microscope lens. There will be a lot of poop and flotsam, and a lot of things that may look like something but are just artifact. Plant materials, fatty globs, food particles and especially pollen can be confusing to sort through. In general, parasite eggs are round or oval and are regularly shaped with smooth sides. The more time you spend sitting at the microscope, the better you get at sorting artifact from significant findings. Learning what isn’t a parasite is just as important as learning what is. You will probably see more artifacts than actual parasite eggs.

I have listed some, but not all, common types of parasites you will find in chicken feces. Anything under the scope that doesn’t look just like these things is probably artifact.

All “worms” are not created equal: Roundworms (nematodes) vs Tapeworms (cestodes)

It’s important to understand the difference between nematodes and cestodes when you’re treating your chickens.

A roundworm (a nematode) is so called because if you slice it like a salami, you will get a round slice. It has, much like animals, a mouth, an anus, guts and a body cavity. There are girl and boy worms that get together. This is not the case with tapeworms (cestodes), which does not have boy and girl worms, guts or a body cavity. Tapeworms are made of tiny segments that each contains ovaries, testes and a humongous uterus full of eggs. Nematodes and cestodes are very different and distinct from each other. This is important because some dewormers kill nematodes in general, and others kill cestodes. What you have in your chickens will dictate what dewormer you use. To confuse matters further, the term “roundworm” in chickens generally refers to Ascaridia.

Ascaridia (roundworms)

Roundworms (Ascaridia) are nematodes found in the small intestine and are very common in backyard chickens. Ascaridia are large worms that are occasionally seen in the feces and rarely, inside eggs (yuck)! Adult worms can be as large as about 10 cm long. If present in sufficient numbers, they can cause a blockage in the small intestine. The prepatent period ranges from about 30 to about 60 days.

Ascaridia galli egg under 40x objective. Note the thick, smooth wall and the dark embryo inside.

Heterakis gallinarum (cecal worms)

Adult cecal worms are nematodes found in the ceca (surprise!) and can infect a variety of birds. These 1 to 1.5 cm long worms are not a problem in chickens unless they are so numerous that they block the ceca. That's a pretty unusual worm load and would only happen very rarely, even in a debilitated chicken. Heterakis are a serious problem in turkeys because the worms themselves carry another parasite (Histomonas meleagridis, which causes Blackhead disease), but in chickens, are considered non-pathogenic. These worms have a direct life cycle and a prepatent period of 3 to 4 weeks.

Heterakis gallinarum egg, 40x objective. These eggs are also thick-walled, but a bit smaller and more narrow than Ascaridia. There may be one or many cells inside.

Capillaria spp (threadworms)

Adult threadworms are nematodes that are about 4 mm long and are found in the crop, esophagus or lower intestinal tract of the chicken, depending on species. These worms can be quite pathogenic in chickens. They have a direct life cycle and the prepatent period is about 3 weeks. Threadworms can be behind a variety of symptoms in your chickens including nonspecific crumminess, diarrhea and depression, especially in young birds. Infection with threadworms can also reduce their resistance to other infections.

Capillaria egg. Note the clear plugs on each end of the egg.

Syngamus trachea (gapeworms)

Gapeworms are nematodes that are aptly named, as the Y-shaped, bright red worms are found in the trachea of the chicken rather than the digestive tract, and can result in gurgling and gaping, which is often confused with other respiratory diseases. The worms are between 1 and 2 cm long, and in sufficient numbers can obstruct the airway. Chickens can become infected with gapeworms by ingesting eggs in the feces of an infected chicken or by consuming an intermediate host, such as an earthworm. The prepatent period is 18 to 20 days.


Gapeworm egg. Characteristic polar plugs and multicellular embryo or larva inside the egg.

Tapeworm eggs and segments

Chickens can be infected with a variety of tapeworms. Some tapeworms will shed eggs in the feces, and others shed moving segments resembling sesame seeds or grains of rice. These segments are each absolutely packed with eggs. Occasionally (rarely) you will even see a whole worm expelled in the feces.

Tapeworms are cestodes, so do not have a body cavity and are pretty much mindless egg factories. They do not have a mouth or a gut and they hang there in the intestine and absorb nutrients through their skin. For this and a few other reasons, these worms generally are not susceptible to the same chemical dewormers that the above “round” worms are (worms with a body cavity).


Note the segments in the worm. Each segment can move on its own. Creepy, right?

Tapeworm egg that shows pretty clearly the distinguishing feature, which is the embryo containing hooks inside the egg. These hooks are what the worm uses to hang onto the intestine of its host.

Tapeworm eggs can vary in appearance but have common characteristics. Look inside the egg and note that there is a series of hooks inside. If you use your imagination, the hooks are generally shaped like the head of an old-style claw hammer.

Here’s a tapeworm segment, I picked it out of fresh feces and put it directly on a slide in a drop of saline and covered with a cover slip. This is called a “Squash prep” for obvious reasons.


A close up of the above squash prep reveals that it’s absolutely packed with eggs.

See all the little hooks inside?

Tapeworms have an indirect life cycle, meaning chickens have to eat an intermediate host in order to become infected. Depending on the species of tapeworm, the intermediate host includes several types of bugs, snails, slugs, rodents and so on. They will not generally cause disease in chickens unless their mass causes intestinal obstruction, which is very rare. They do absorb nutrients from their host, so may reduce production in severe cases.


Coccidia are the parasites that cause the disease coccidiosis. These are completely different than the worms discussed above, and are single-celled, microscopic organisms.

There are several different types of Eimeria (coccidia) found across many species of animals and are by far the most common intestinal parasite in chickens. They are very species-specific, so they cannot be transmitted to chickens by other birds or animals.

Coccidia are not worms (so are not nematodes nor cestodes) but are single-celled protozoa that reproduce inside the cells lining the intestinal tract. Different coccidia species occupy different areas of the intestine. They can reproduce in huge numbers, and in doing so, rupture the cells lining the intestinal tract, causing sometimes very severe disease with high mortality in young chickens.

They are especially tricky to treat since they live in such large numbers inside body cells. Instead of killing off the coccidia, drugs used to treat coccidiosis act to stop these parasites from reproducing (coccodiostats) but will not eliminate them. For this reason, you should not expect your chickens to be completely clear of coccidia when you do fecal exams. The immune system must be able to control coccidiosis. Most chickens are exposed to coccidia early in life, and once their immune system develops fully, they are able to keep it in check. Coccidiosis is a disease of crowding, so keeping your coop clean and dry and avoiding overstocking will help prevent coccidiosis in your flock. Coccidiostats are ineffective against nematodes and cestodes, and drugs used to treat nematodes and cestodes are ineffective against coccidia.

Coccidia oocysts are commonly present in the feces of even healthy chickens so do not be surprised if you find a few. Oocysts are very small compared to worm eggs. They can have one or two or sometimes a few nuclei and can vary from round to egg-shaped.


Eimeria (coccidia) oocyst under a 40x lens. Note the size difference between worm eggs shown above. Oocysts also tend to have a sheen or iridescence. This is as big as they get. They are always a single cell.
About author
Sue Gremlin
Research scientist in veterinary pharmaceutical industry. MS (biology), MPS (Veterinary parasitology, degree expected May 2020)

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Your articles have come just in the nick of time. I have been wanting my own microscope so I can keep a close watch, not only of my flock of 37 chickens, but my herd of 6 horses, and my pack of 7 dogs. Heck, I might even test my DH for worms! :eek: Uh, no! Just kidding on that one.:gig

All jokes aside, reading your articles has lit a flame inside of me and reminded me how much I loved my bio and chem classes.

Thank you for sharing your knowledge and time with the BYC community. It is much appreciated. :bow
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What a great series of articles. The writing is outstanding, making it easy for a anyone to understand. The processes described, from sample, to reviewing the sample under the microscope, and finally, interpreting what you'll see in the sample is very well organized and easy to understand.
Finally - the details pertaining to the individual type of worms is valuable, even if you choose to have a vet do the test for you - and then you treat your chickens.

Wonderful article that should be in a "Must Read" section somewhere on this site!
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Thank you.


Excellent. I've done my fecal floats for my horses for several years now. But I love the clarity of this article. (all parts) For my horses I use the Mcmaster method but it's great to try and do the method for chickens. I hadn't tried that method yet. Thank you.

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