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Aspergillosis in laying birds

Course: Poultry diseases and pests | Last Updates: 7th October 2015

Michael Clark
Director Minster Veterinary Practice in Leicestershire
Biography >>

Lower straw quality, resulting from wet weather during harvest, leads to an increased risk to bird health from diseases, such as aspergillosis, caused by exposure to moulds.

On top of this, the dramatic slowdown in the construction industry has meant alternative wood-based bedding, such as wood shavings, is in short supply. Consequently, sawdust and shavings are a more expensive option for bedding than straw.

This has forced some producers to switch to straw, which has brought unexpected consequences for the health of some flocks.

What is apsergillosis?

mould-sporesAspergillus is a genus of about 200 moulds found throughout the world. They are aerobic and are found in almost all oxygen-rich environments, where they commonly grow as moulds.

But in terms of poultry disease, the key species is Aspergillus fumigatus. Exposure to this species can cause aspergillosis, which is a disease of the respiratory tract. It is frequently referred to as brooder pneumonia.

It affects commercial ducks, turkeys, game birds and laying hens that use straw in the scratch areas of poultry sheds.

How do birds become infected?

The mould thrives in warm, wet conditions, producing black straw. Spores produced by the mould can then enter the bird’s lungs and affect their ability to breath.

It can also be egg-borne in a hatchery. Unhatched eggs after the incubation period will be cracked open and aspergillus can sometimes be found.

Aspergillosis is not usually passed from bird to bird, it is usually spread via a bedding problem. Therefore, young birds can be infected either by an egg infection or by contaminated straw.

For older birds, the infection is more likely the result of an environmental problem from bedding contamination.

As aspergillus likes a warm, humid environment, a poultry shed heated to temperatures that are sometimes as much as 25°C, provides the perfect environment for its growth.

Recognising the symptoms

Signs of the disease to look out for are birds gasping for breath and an increase in mortality levels.

In young birds, there are not many symptoms that are visible, but there will be a rise in mortality. However, older birds can be seen gasping for breath.

Clinical signs also include a swollen head, coughing, sneezing and ruffled feathers.

Ducks and turkeys are particularly affected by aspergillosis where mortality levels can be as much as 10%.

If there are any unexplained increases in mortality in a flock, a post-mortem should, ideally, be performed.

Usually, the respiratory system will show white nodules – this is a classic sign of aspergillosis. Then by testing the nodules further and growing and identifying the mould on plates, you can confirm if it is aspergillosis.


The disease can cause an acute respiratory condition in the first three weeks of life that could see mortality rates ranging from 5-50%. And survivors often develop chronic disease with up to 5% mortality.

However, if litter is wet, further cases can occur. The wet conditions can produce sufficient fungal growth that may continue to produce new cases of the infection for some time, as the litter dries out and becomes aired.

Is aspergillosis on the increase?

There has been a rise in the number of cases of aspergillosis. We believe this is because of the poor harvest brought on by the 2008 wet summer, as the growth of Aspergillus fumigatus is stimulated by humid conditions.

This is backed up by the GB Avian Disease Surveillance quarterly report published by the Veterinary Laboratories Agency in autumn 2008, which warned that the increased number of cases of the disease will occur until this summer, when new crop straw becomes available.


Replacing the straw for better quality bedding will help reduce aspergillosis and its effects.

However, as shavings are expensive in the current climate and with the broiler industry predominantly using shavings, egg producers need to be wary of poor quality straw that is currently available.

Once there is infection, there is no treatment available for aspergillosis in the UK. The best solution is to separate the birds from the infection.

This is done by indentifying the source and separating the healthy birds from the straw and the source of infection.

Culling is not necessary unless the birds are seen to be suffering.


For hatchery-borne infection, prevention involves collecting and storing eggs ready for hatching in appropriate storage that reduces the effects of sweating and protects them from exposure to moulds.

And equipment in the hatchery should be monitored regularly and kept clean to prevent contamination of spores.

On farms, prevention includes using a good quality bedding material that is free from mould.

Some bedding manufacturers treat their products to remove spores. For example, Sundown Straw Products adds Sal Curb F to straw to prevent mould and spore growth, Snowflake Woodshavings uses a dust screening process to prevent spore growth and Easichick treats its bedding with organic acids prior to packing.

layer-hens-on-strawThen there are newspaper-based bedding products, such as Galloway Recycled Newspapers’ Shred-a-Bed. It claims that newspapers are sterile and don’t hold the spores that cause infections.

However, if you are using standard straw, there are measures that can reduce risk, such as avoiding using bales that are visibly blackened. In addition, keep bedding stored in a cool and dry environment to prevent mould growth and spores from developing.


  • Fungal disease that infects the respiratory tract of birds
  • The disease thrives in warm, wet conditions
  • It is associated with mouldy straw
  • Cases of the disease have risen since last autumn because of a wet summer and poor harvest
  • Young birds can be infected by an egg infection or straw contamination
  • Older birds will be infected by an environmental problem and can be seen gasping for breath
  • Separate the healthy birds from the infected straw and the source of infection 

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