Dust and diets – an unholy alliance

Dust and Diets: An Unholy Alliance in Bird Care

Haith's have long been recognised and widely praised for the quality of their  foodstuffs, that any fed to birds, wild or captive, are as free as possible from dust. Indeed, in 2014, in a presentation to BIAZA (The British and Irish Association of Zoos and Aquariums) Haiths's coined the phrase “Dust is a dirty word at Haith’s”. They explained that, while since 1937 dust has never been welcome in their bird diets, their concern about it had grown exponentially. At the same time, they quoted me, their veterinary advisor, stating that “dust is harmful to a bird’s respiratory system and extraneous husk can damage delicate tissues and allow entry of pathogens”.  I can now add that dust does much more than that; it not only irritates and inflames a bird's trachea, lung and air sacs, but can also act as a mechanical carrier for bacteria, for fungal spores and possibly for viruses. This latter danger was emphasised in an article by the leading aviculturist Fred Wright in Cage & Aviary Birds April 30th, 2014 entitled “Our small but deadly enemy”.

What exactly is dust? It consists of fine particles of solid matter, each of which may have a diameter of less than half a millimetre (Figure 1.) 

Dust under the microscope

Figure 1. A photo down the microscope of dust removed from an uncleaned food sample. Note that the particles vary in size, structure and shape, all of which influence how they might affect the delicate respiratory tract of a bird.

So-called “inhalable” dust consists of large, usually heavier, particles which is visible to the naked eye and tends to get trapped in the nose, mouth, throat or upper respiratory tract. In contrast, “respirable dust” is so fine that it is invisible to the naked eye and can be breathed deeply into the lungs or the air sacs of birds.

Much of the dust in the air comes from soil, pollution and volcanic eruptions. It can travel a long way. Dust from the Sahara, for instance, crosses the Atlantic and regularly causes environmental and health problems in Trinidad and other countries in the Caribbean.

An alarming report in November 2021 revealed that even plastic particles can exist as “dust” and be inhaled; see How damaging is breathing in microplastics? - Plastic Soup Foundation

The dust associated with grain, including cereals, is acquired during harvesting; if not cleaned, the dust will find its way into animal and human food.

Dust indoors is more likely to comprise pollen, human and animal hair and tiny pieces of sloughed skin but it can also be liberated when old books and documents are handled. 

The dangers of dust to animals – and to humans who work with them - was recognised many years’ ago. For example, it has long been known that horses exposed to dusty hay, straw or housed in a poorly-ventilated stable can develop lung damage (Figure 2).


Figure 2. Horses exposed to damp fodder, such as hay or straw, may be exposed to dust, bacteria and fungi – as might the geese in the background in the picture. 

Humans working in dust-laden environments may develop allergic reactions leading ultimately to pulmonary disease, such as emphysema (destruction and dilatation of the lung tissue) (Figure 3). Emphysema can also result from prolonged exposure to fumes from heating fuel or car exhaust and particulate material from wood and mining products.


Figure 3. A section of a lung from a man who died several years ago following severe respiratory disease. The black areas are dust, inhaled during his work as a coal miner.  The paler areas in the picture are emphysema” – over-dilated and badly-damaged lung as a result of long-term irritation and loss of elasticity. 

Dust bronchitis is another condition that affects humans and animals. The bronchi are damaged by the mechanical and chemical effects of inhaled dust particles on their lining mucous membranes and an inflammatory, not an allergic, response results. 

A few years ago awareness of the dangers of dust prompted scientists and vets to introduce “dust-free bedding” for animals kept in laboratories for scientific studies. Keeping such animals free of respiratory disease is vital if, for example, they are to teach us more about coronaviruses and permit reliable testing of vaccines and antiviral agents in the global fight against Covid-19.

Over the past two years further information has strengthened the argument that dust and other particulate material can be extremely dangerous to birds – and other species.

As far as birds are concerned, a paper entitled “The Avian Respiratory System and its Non-Infectious Ailments: A Review” by Peernel Zwart and Jaime Samour, published in February 2021 in the Journal of Exotic Pet Medicine (volume 37(5)) was of great significance. The authors explained that the avian respiratory system is well-adapted to withstand insults but chronic irritation can lead to a condition called "bronchiolar associated lymphoid tissue".

Even more significant is greatly increased awareness, because of the Covid-19 epidemic, that a damaged respiratory tract is very susceptible to infection by viruses, including SARS-CoV-2 coronavirus. Studies in human patients and animals have confirmed this synergistic effect. Covid-19 itself is primarily transmitted in a similar way to dust – the virus is in the form of tiny particles that are passed out when an infected person exhales, especially if speaking. They remain in the air, like dust or smoke, and accumulate; they can then be inhaled by another person.

Research on coronaviruses started decades ago when vets and animal scientists were investigating a disease of domestic poultry that affects the respiratory tract, intestine, kidney and reproductive system. It was called infectious bronchitis (IB) and was the first coronavirus described. Its control nowadays is based on a combination of vaccination and hygiene, especially improved ventilation – just like human Covid-19!

Dust is also linked with climate change. Wild fires in Davis, USA, were recently reported to have adversely affected the health of macaque monkeys kept in a primate centre. It seems likely that smoke (a form of dust) from such fires are having important but non-lethal effects on indigenous and captive wildlife – and humans – in various parts of the world.

The problem is not restricted to smoke. Millions of children all over the world inhale polluted air every day and countless deaths result. The cause is largely, but not solely, the burning of fossil fuels, which liberates fine particulate material (dust) into the atmosphere. This was one of the targets of The Earthshot Prize, a major new initiative that was launched by Prince William and The Royal Foundation in October 2020. See: Clean our air - Earthshot Prize

All of the above amounts to a global crisis that is characterised by contamination of the environment by various types of particulate matter – dust. Foodstuffs for animals are only a tiny part of the problem, but not unimportant.

In the context of grain-based diets, it is now crystal clear that unclean seeds can both cause and predispose animals and humans to respiratory disease. In particular, my research over the years has confirmed that far more potentially harmful bacteria and fungi (in terms of both numbers of colonies and species of organisms) grow from a dusty, dry seed mix than would be expected from a properly cleaned diet. 

Dust presents a particular danger to birds because it can not only irritate and inflame their specialised and sensitive respiratory tract – see above – but also act as a carrier for potentially pathogenic (disease-causing) organisms including fungal spores (Figure 4. )


    Figure 4. Aspergillus fungus (stained black in these pictures) can be inhaled from dusty, uncleaned, seeds and may invade the lungs, causing aspergillosis - an often untreatable disease of birds. 

    Some manufacturers recognise this danger and John E Haith (Haith’s), in particular, has tackled the problem energetically. Staff at Haith’s use their skills and experience to screen raw materials for the presence of dust (Figure 5.) and each seed is “super-cleaned”.

    Figure 5. A skilled member of Haith’s staff examines raw materials for the presence of dust.

    The company’s quality control (QC) programme, established in 2012, permits random samples of products to be examined using laboratory tests (Figure 6.) including studies on appearance, odour, consistency, flotation (which helps detect any residual dust/other particulate matter), microscopical examination of smears, bacteriological and mycological culture and repeated checks for invertebrates.

    Figure 6. A sample submitted by Haith's is examined independently in the author's laboratory. 

    Seed is ultimately passed (or rejected) by Haith's QC before being approved for sale.

    A statement by Haith’s eight years ago is worthy of repetition today “Dust has been unwelcome in our bird diets since 1937. Now it’s a four-letter word!” It is clear beyond doubt that uncleaned, dusty, food can harm birds and sometimes kill them. They deserve better.

    Professor John E. Cooper FRCVS

    22nd January 2022

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