Have you ever been out in the woods and accidentally stepped on a Puffball mushroom and been surprised to have released a cloud of spores? I remember as a kid delighting in finding them just to be able to stomp on them. Afterwards my shoes and pants would be coated with a fine trace of spores.

Exploding Puffballs
Exploding Puffballs

Most of us probably don’t think about how fungi and molds might affect our chickens, but they do, and the results can be deadly. I’d never given much thought to the existence of fungi in my chicken pen, other than to avoid feeding them moldy bread or use bedding containing mold. It wasn’t until a few weeks ago, when I had a young pullet suffering from paralysis, that I learned about the potential dangers of mold.

There are a number of pathogens and toxins in our everyday environments that can cause illness in chickens. One of them, aspergillosis, a fungal disease seen world-wide infecting both people and animals, is caused by inhaling Aspergillus fungi (mold). If you leave a loaf of bread on your counter for a couple of weeks, chances are it will become colonized by one of a couple hundred species of aspergillus mold, which favour starchy foods like potatoes, cereals and rice.

The spores might be found in contaminated feed, moldy bedding, poop, soil or damp places within the coop. The fungi can penetrate eggs and infect the chicks, and if the eggs are broken they can release spores inside the incubator. If the hatchery is the source of the infection it’s termed ‘brooder pneumonia’.

Once inside the body it may affect various systems, but is most often seen as a lower respiratory tract illness. Like many other pathogens, aspergillus is commonly found throughout the environment and can exist in low numbers without causing any harm. Sick or stressed birds are always more vulnerable to infection.

Symptoms vary depending on the location of the infection, a bird’s age and immune status, and amount of Aspergillus they were exposed to.

Acute form: rapid onset caused by exposure to large amounts of aspergillus.

  • Most common in young chicks
  • Death occurs within a few days
  • Gasping
  • Tail bobbing
  • Open mouth breathing
  • Sudden depression
  • Decreased appetite
  • Delayed crop emptying/impacted crop
  • Blue/purple comb and wattles

Chronic form: more subtle onset, taking several weeks or months to develop.

  • Lethargy
  • Change or loss of voice, more apparent in roosters by lack or change in crowing behavior
  • Weight loss
  • Coughing
  • Open mouth breathing
  • Blue/purple comb and wattles
  • Depression
  • Decreased appetite

Disseminated aspergillosis: involves lesions in the brain and neurological symptoms:

  • Weakness
  • Loss of control of body movements
  • Paralysis
  • Wry neck
  • Repeated falling on side or back
  • Difficulty moving
  • Tremors
  • Depression
  • Drooping wing
  • Unsteady gait

Ocular Infection of the Cornea:

  • Sticky, swollen eyelids
  • Eye swelling
  • Eye discharge
  • Eyelid spasm
  • Sensitivity to light
  • Cloudy cornea
  • Cheesy yellow discharge from the eye

The prognosis for a bird suffering from aspergillosis is not bright. Early diagnosis and treatment is difficult because of the lack of symptoms until the disease is more advanced. Sometimes you can figure it out through a process of elimination and studying the symptoms. A blood panel may show an increase in white blood cells, but not until the later stages of the disease. Fungal cultures can be taken of the trachea, air sacs, or throat.

If you’ve got an experienced vet and have deep pockets, diagnostic work can include a complete blood count, aspergillosis antigen and antibody levels, x-rays, endoscopy and fungal culture.

Unfortunately even with a diagnosis in hand, the treatment is lengthy and difficult: usually 4-6 months of administering systemic anti-fungal medications. Most of us are not prepared to undertake that regimen and most birds will succumb without ever recovering.


  • Ensure your coop has good ventilation, with vents and opening windows, to ensure regular airflow.
  • Remove any leftover feed or decaying vegetables or fruit daily.
  • Avoid using straw or hay in wet weather, as it is likely to mold.
  • Rotate location of feeders and water dispensers to prevent growth of mold.
  • Remove mold on hard surfaces with water and detergent and dry completely.
  • Avoid using absorbent materials in your coop construction.
  • Reduce the potential for condensation on cold surfaces by adding insulation.
  • Minimize use of antibiotics and corticosteroids.
  • Don’t use corncobs or walnut shells for bedding.
  • Avoid social stress in your flock (i.e. new birds, changes in the pecking order).
  • Ensure your coop and pen aren’t dusty.
  • Feed a well balanced diet and ensure your flock is not deficient in vitamin A.
  • Clean your coop on a regular basis.

Other illnesses that share similar symptoms with Aspergillosis: Marek’s Disease, MG (Mycoplasma Gallisepticum), gapeworm and other respiratory diseases.

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