PROTECTING the ‘shell’ of poultry sheds from infectious diseases such as avian influenza should be a priority for farmers looking ahead to this coming winter.

AI remains an environmental threat, and it is expected that, when colder weather returns, infection pressure will almost certainly ramp up again.

See also: 5 lessons learned from the 2021/2022 AI outbreak

“There is a very small infectious dose for this virus – one single bird dropping has thousands of infectious doses,” says Andy Paterson, head of intervention and epidemiology at the APHA.

He gave a recent Poultry Health And Welfare Group conference an overview of some of the issues that APHA investigations had uncovered on farms hit by avian influenza in the 2021/2022 outbreak.

“Petrol and a match”

Many were caused by a single small introduction of the virus – in some cases, it was possible to trace how an infection had entered a shed from a small hole in a ceiling and spread rapidly through a flock.

“It was a bit like a petrol and a match,” explains Mr Paterson. “You just need one spark and then it goes off – we’re talking very low levels of virus.”

While that sounds challenging, there is a lot that farm businesses can do today to minimise their risk as winter approaches. 

Protect the shell

The most stringent focus should be placed on securing the “shell” of the poultry shed itself. While good biosecurity is essential across a site, protecting the interior of units that house birds is a critical step.

Ensuring staff are on board with biosecurity measures is a fundamental to a biosecure farm.

The virus enters sheds in one of three ways – through the gate, over the hedge or from the sky, says Mr Paterson.

Walking it in

“The biggest risk is around your buildings, and someone walking or driving the virus into the bird environment – protect the entrances to your sheds.

“You can’t keep the area around buildings infection-free – it’s just too big. You should devote most of your efforts to the buildings themselves.”

That means making it difficult to enter a shed without taking measures to change into clean, dedicated clothing and disinfected footwear.

‘Culture of biosecurity’

Mr Paterson says a major takeaway from this most recent outbreak is implementing biosecurity – ideally as a director-level responsibility – with all the accountability that brings.

It should be a part of the company’s culture – and all levels of staff should not only be doing it – but be seen to be doing it as well.

He likened the attitude to that of Health & Safety requirements, which over time have become accepted as a far more important part of most people’s working lives.

Set an example

Staff should be provided with dedicated boots and overalls for each shed, and everything should be colour coded to make it obvious that the right equipment is being used in the correct area.

Area managers and other essential company visitors should always set an example, which will help to ensure continuity across multiple sites within the same company.

Many of the outbreaks last year were associated with non-routine events like staff absences or relief managers covering where they don’t typically work.

Record keeping

Stringent record keeping is essential, adds Mr Paterson, with contact tracing and licencing entirely reliant on farms’ accounts of bird, feed and people movements. 

They need to be readily available in the event of an outbreak, as nothing can happen without APHA being satisfied of tracing.

One takeaway from outbreaks was that electronic records are often quicker to send and interpret – thousands of hours were spent last winter transcribing often illegible and incomplete visitor sheets.

Recording and analysing bird performance daily should be commonplace, too. It can be an early warning of a health challenge, meaning that a potential infection can be ruled out or confirmed much more quickly.  

Building integrity

Fixing the roof while the sun shines is a well-known saying, and has an application for farmers considering how to best prepare for the coming winter.

Building integrity is critical – water ingress through rain, wild bird entry and rodents are all potential ways for AI and other diseases to get into sheds.

There’s increasing evidence that bedding can be a major risk factor. Keeping it wrapped and undercover are important steps to take where possible.

Look to access points

Any area open to the outdoors should be scrutinised as far as possible, including muck belts, ventilation inlets and the condition of doors or pop holes, in particular at their base.

Where possible, mesh or wire wool should be used to close any gaps that birds or rodents may use to enter sheds.

Moss on roofing has also been identified as a potential problem – it attracts wild birds as food and bedding, and droppings they leave behind can leach into sheds when it rains.


Unusual weather events can also contribute to health challenges – high winds have damaged the structure of sheds, while flooding is considered an important factor in introducing infection in some cases.

Extreme weather is also changing wild birds’ behaviour, and there have been examples of wild birds found in non-typical parts of the country blown off course or choosing to settle in a different habitat.

Open bodies of water have also been identified as an attractant to wild birds and, therefore, a risk factor. They should be netted where possible, particularly when close to poultry farms.


Last winter there were a number of “clusters” of cases identified, says Mr Paterson, both geographical and within companies.

“The overriding thing is that we found a large number of biosecurity issues in these large clusters – but we can’t categorically rule out that there wasn’t one simultaneous dump of infection from wild birds at one point.”

However, once restrictions were put on all trace premises, there were no more new infections, indicating an element of infection moving around companies.