Last month, we discussed external parasites. Today, we are going to look at the worms who live inside our chickens.
There are 3 groups of worms: roundworms, flatworms, and thorny-headed worms. We will focus on the first two as the latter despite their devilish name are rarely a problem for chickens.
Worms reproduce and lay their eggs inside the chicken. Their eggs are expelled from the chicken via her poop. Then depending on their species, the eggs infect new chickens either directly or indirectly, meaning that the eggs are directly eaten by another chicken, or that the eggs are eaten by an intermediate host (fly, earthworm...) which is then eaten by a chicken.
About half of the roundworms have a direct life cycle, while the other half and all of the flatworms have an indirect life cycle.
Roundworms (also called nematodes) are worms with a long round body. There are lots of different species of roundworms, each invading a different organ: the large roundworm, the capillary worm, the crop worm, the eye worm, the stomach worm, the cecal worm, and the gapeworm. Let’s have a look at the two most common roundworms in North America.
The large roundworm (Ascaridia galli) is thick and can reach 4½ inches long thus is easily visible with the naked eye. They live in the small intestine and interfere with the absorption of nutrients. They damage the intestine walls and can create a blockage that eventually results in death. They have a direct life cycle.
The cecal worm (Heterakis gallinae) is white, thin, about half an inch long and also relatively easy to spot in droppings. They have a direct cycle and are not posing any major threat to chickens. But they can carry blackhead disease (Histomonas meleagridis) which chickens are typically resistant to but is a death threat to turkeys as we unfortunately experienced ourselves with the loss of Lucie.
Flatworms have a flattened body that looks more like a ribbon than a tube. From the two versions of flatworms, the tapeworms (also called cestodes) are the more problematic in North America. Most of our backyard chickens are infected by them. They live in the different areas of the intestine. Their life cycle is indirect with earthworms, beetles, flies, snails, slugs, termites, or ants as the intermediate host. The body of a tapeworm is composed of many segments, and each segment may contain hundreds of eggs.
Healthy chickens can tolerate a certain amount of worms, so there is no need to deworm them regularly. Actually, deworming your chickens on a schedule builds a resistance to dewormers. Only deworm after doing a fecal test to confirm that there is indeed a worm invasion and which species you are dealing with. Fecal tests should be included as part of your regular health checks as well as anytime a chicken shows signs of not doing well (diarrhea, weight loss, pale comb and wattles, lethargy, gasping, reduced egg production) or when you see worms in her droppings or eggs.
Let’s now talk about treatments. All dewormers are off-label for egg laying hens.
Albendazole is a broad spectrum dewormer and is effective against all types of roundworms and tapeworms. We use the 11.36% oral suspension from Valbazen at a dosage of 0.08cc per pound of bird, and then repeat in two weeks.
Fenbendazole is effective against all worms except for some capillary species. It comes in different forms (liquid, paste, powder). We use the 10% paste from Safe-Guard at a dosage of 1 pea size per bird and then repeat 10 days later.
Ivermectin is effective against all roundworms. It comes in different forms. We use the 1% injectable form and give it orally at a dosage 0.01cc per pound of bird and then repeat in 2 weeks.
Piperazine is effective only against the large roundworm. Use at a dosage of 100mg per bird and then repeat in 7 days.
If one chicken needs to be dewormed, treat everyone to control the infestation.
It’s important to not always use the same dewormer and to rotate them to avoid building resistance.
As with any drugs, residues may be found in the eggs. Since no dewormers are approved by the FDA, there is no data on the egg withdrawal time. “If you cannot determine a specific drug's withdrawal period, allow at least 30 days.“ according to Gail Damerow in The Chicken Encyclopedia.
You may have heard about some natural worm control such as brassicas (cabbage, cauliflower...) and cucurbits (cucumbers, pumpkins...), garlic, wormwood, etc. Be aware that no definitive studies on their effectiveness have been done. They may have some effect in preventing worms but not to remove them. So if your chickens have a worm infestation, you will need to use one the treatments listed above.
As you all know, prevention is better than cure.
Keep a clean coop. Don’t allow the droppings and the worm eggs they potentially contain to accumulate. Clean often (we pick up the poop daily in the hen house and weekly rake the run) and replace the dirty bedding. The more chickens you have and the smaller your coop, the more often you need to clean.
Keep their feeder and waterer poop free. Don’t give them food or treats directly on the ground that may be contaminated. Use dishes instead.
Control intermediate hosts (fly, earthworm, snail, beetle, slug, grasshopper...) as they carry the worms with an indirect life cycle.
If you have turkeys, keep them in a separate yard away from the chickens.
In short, worms are common in chickens. Chickens can deal with a certain amount, but an infestation can kill them. Worms are easily treatable, but only deworm after a positive fecal test.
Chapter 6 “When Chickens Get Wormy” from The Chicken Health Handbook, 2nd edition, by Gail Damerow