A Fungus Can Harm Chickens, So Protect Your Flock

Omnipresent in our environment, fungi can cause serious illness in poultry flocks. Here’s a look at five of the most common fungal diseases and mycotoxins that can affect our fowl. 

by Ana Hotaling
PHOTO: Fotokon/AdobeStock

As poultry keepers we know that, despite our best attempts at biosecurity and no matter how carefully we keep our coops, occasionally something will evade our efforts and affect our flocks. A sweltering, high-heat day may induce deadly heat stress. Or bacteria unintentionally carried in from a visitor’s farmyard can cause life-threatening contagion. The predatory attacks can present a constant threat depending on where you live.

Our poultry suffer so many potential perils. How do we even sleep at night?  

Still, by keeping a secure coop and restricting access to your birds, you do everything possible to keep out uninvited guests. But what if what’s affecting our chickens isn’t a guest but a fungus, an established presence in the environment?  

Fungus Among Us

Fungi (the plural of fungus) are unicellular and multicellular organisms that thrive throughout the world. They do not rely on photosynthesis for energy but rather derive their nutrition directly from absorption. They secrete enzymes onto the surfaces they grow on, absorbing the nutrients those enzymes digest.

Taxonomists have identified approximately 100,000 varieties of fungus and believe there may be as many as 1.5 million in the world. While most of these are harmless to other living organisms, several are not. In specific conditions—darkness, temperature, and humidity are all crucial factors—these fungi can produce toxins called mycotoxins that can cause disease and, in extreme cases, death amongst our chickens.  

Unfortunately, it is not easy to tell when a fungal disease affects our flock. Unlike viral or bacterial infections, fungal diseases for the most part do not cause such visible symptoms as sneezing, mucous discharge or lethargy. Diagnosis is usually done by microscope, often at the necropsy table.

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If you sense a general unwellness amongst your flock, trust your instincts. Fungus may very well cause one of these five fungal conditions in your chickens. 

Read more:Use essential oils for a clean, healthier coop.


Aflatoxicosis results from highly toxic mycotoxins produced by the fungi Aspergillus flavus, and Penicillium puberlum. These toxins are collectively called aflatoxins. They can establish a tenacious, extremely stable existence in poultry feed.

Afflicted birds display a lack of appetite, an unsteady gait and a tendency to lie down. Anemia and black or bloody diarrhea may develop. Aflatoxicosis has a high mortality rate, and necropsies will show enlarged kidneys and enlarged, discolored liver.  


Most commonly caused by the fungus Aspergillus fumigatus, aspergillosis can affect all domestic and captivity-raised birds—your chickens, of course, but even zoo penguins are at risk. Younger birds are more at risk to this disease, which causes lesions in the lungs, air sacs and trachea, causing afflicted animals to gasp for air.

Chickens and pigeons may occasionally develop painful, itchy lesions on their skin as well as inflamed eyes. Aspergillosis will affect an entire flock versus a handful of birds, with a high mortality rate.  

Read more: What should you do after an unexpected chicken death?


Also known as thrush, candidiasis is caused by Candida albicans, a saccharomycete fungus more commonly called yeast. C. albicans typically resides within the gastrointestinal tract of animals (including humans), participating in the digestive process and kept in check by the presence of beneficial bacteria.

Candidiasis typically occurs when long-term antibiotics have been used. These antibiotics not only kill off harmful bacteria but the helpful flora as well. This allows C. albicans to flourish unchecked.

Candidiasis can be identified by the thick, bright-white mucus that coats a chicken’s tongue, mouth and esophagus. Oral mucus produces a  characteristic strong, fruit-like odor. Fortunately, candidiasis can be treated with an antifungal, Nystatin, available via prescription from a veterinarian.  

Trichothecene Mycotoxins 

This group of toxins results from many different types of fungus, including Trichothecium, Trichoderma, Stachybotrys and Fusarium. Trichothecenes can adversely affect any animal, from chickens to humans.

These toxins are most commonly associated with spoiled grains such as oats, corn, barley, wheat and sorghum. When continually ingested by chickens, the mycotoxins cause weight loss, decreased appetite and a drop in egg production. Trichothecenes can cause cysts on birds’ feet and legs, as well as ulcers in their mouths.  

Zearalenone Mycotoxins 

Produced by such fungi as Gibberella zeae, Fusarium cerealis and Fusarium crookwellense, the zearalanone mycotoxins are commonly found in improperly stored animal feeds and cereals.

Zearalenone exposure is pernicious. It is an estrogenic toxin, meaning it attacks the reproductive systems of the afflicted animals. Zearalenone’s mechanisms are not yet fully understood beyond the fact that it severely affects reproduction. Afflicted hens will experience a decrease in egg production and develop peritoneal and oviductal cysts, detected at necropsy.  

Preventative Measures 

As dangerous as these fungal conditions may be to your flock, you can easily prevent a dangerous fungus from reaching your chickens. First and foremost, store your poultry feed in an airtight container in a dry environment. Humidity can encourage the growth of fungus.

Never feed your flock any feed, scratch, kitchen scraps or other edibles that contain mold or appear clumpy or fuzzy. Dispose of these well away from where your flock ranges.

Establish a routine schedule that involves the thorough cleaning and sanitizing of all of your feeders, including feed lines and feed-storage containers. Buy your feed from a trusted source and regularly inspect your feed grains, especially corn.

If you live in a region known for high humidity, consider using feed additives such as zeolites, clays and propionic acid to control the growth of fungus in your feed.

Finally, frequently clean your coop. Replace moist, soiled litter with fresh, dry bedding to reduce the possibility of fungus establishing itself in your flock’s living quarters.  

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