Biosecurity: The "inner shell strategy"

In a ranking of the challenges faced by poultry farmers in 2022/3, Avian Influenza has to be up there.

Housing poultry has certainly slowed the virus down, but it is still able to access flocks using the only two routes available to it:

1. Through the building structure
2. Through the biosecurity

Speaking at the 2022 BFREPA Conference in October, the UK’s Chief Veterinary Officer (CVO), Christine Middlemiss, acknowledged that “biosecurity in free range is not all about housing…your biggest risk is around your buildings” going on to say that “housing of free-range hens will give a 2-fold reduction in the likelihood of infection” whilst good biosecurity around the house would “bring an overall 44-fold reduction in risk”.

There is more information below on the measures to prevent the AI virus gaining access to pullets and laying flocks, with the emphasis on securing both the flocks and the premises. We also explain why H5N1 causes more problems, the wider advantages of biosecurity and why producers need to link this to wider flock health – and think beyond AI – to maintain and enhance profitability.

Avian influenza – a 2022 recap

Avian Influenza infections in 2021/2022 were dominated by the H5N1 Highly Pathogenic strain of the virus, that had previously been circulating in Europe. The predominance of this strain has changed the dynamics of the disease, compared to the previous seasons’ dominance of H5N8. H5N1 has proved to be far more infectious and has also spread widely through the wild bird population.

Along with the increased chance of encountering the virus, is its increased virulence, with only very small initial quantities of it needed to readily infect and spread in avian populations.

Biosecurity. The “inner shell strategy”

The integrity of the housing itself has often been at fault due to poorly maintained walls, doors, windows, ventilation inlets, and roofs. Leaking roofs and guttering can create a constant stream of viral soup into the house from wild bird faeces on the roof. This is compounded by moss on the roof which encourages wild birds. In some cases, broken or absent mesh or seals create openings for virus vectors, which can include rodents as well as birds.

Defra epidemiologists who have looked at outbreaks on free range egg farms have found that the weaknesses are generally within the inner shell of the farm, particularly around entrances to houses and the lack of a lobby with separate clean/ dirty areas, no dedicated house PPE (not disposable foot coverings), poor foot dip locations, incorrect dilution and no dedicated brush, no washbasin or hand sanitiser, and a lack of secure doors. Issues have been found in the egg room where it serves as a lobby into the poultry accommodation. Staff working in the egg room can then be responsible for the transmission of the virus into the house via the egg belt.

Biosecurity measures should reduce the risk to a flock, the closer you get to the house. When considering or planning your approach, the three key stages to consider biosecurity are:

• Site planning (conceptual)
• Building design (structural)
• Site management (operational)

Site design (conceptual)

Biosecurity should be considered from the outset – it’s much easier to alter a plan than a finished site – and focus on isolating the flock from physical sources of infection.

Things to consider:

• Access routes: Have a single point of access, gated and secure with vehicle washing and disinfection, plus foot dip, and sign in for all passing on to site
• Proximity to waterways (ponds etc)
• Proximity to migratory birds: And make the site as unattractive as you can to wild birds e.g. anti-perching devices, enclosed storage for feed and bedding etc.
• Drainage: Try to select a range with natural drainage to prevent pooling of water on the range, when locating new houses
• Distance: From other farms, public footpaths, roads and the amount of poultry traffic there is or will be

Building design (structural)

The need to prevent wild animals and birds accessing the flock is well documented and is particularly important to stop the spread of AI. It survives well in wet conditions and with water serving as a vehicle for the virus, it can easily be transported around a site. For example, water can collect on concrete aprons, parking areas and approach paths with flaws in a building’s structure allowing leakage into the flock housing. Preventing the ingress of this potentially contaminated water is vital to defend the flock. The design and ongoing maintenance of buildings is therefore key to effective biosecurity.

• Drainage: Doors with level access must be protected against water ingress, particularly when rainfall is heavy. Consider sandbags to keep water away from the base of doors
• Materials used: Easy to clean and maintain, reduce ingress and serve as a barrier to wildlife (rodents). Ensure doors, vents, intakes and ducts are all sealed into the building structure preventing wildlife and rainwater from accessing the flock
• Feed augers and muck conveyors: Check they’re well sealed, both in to and out of the building
• Roof structure: Is wind and watertight, and there are no leaks when it rains
• Roof ventilation: Is enclosed, so wild birds cannot nest
• Tunnel vents: Rather than side vents to avoid uncapped vertical fan vents
• Gutters: Should be high capacity, easy to access for cleaning, with sealed piped discharge taking contaminated roof water away from the house
• Drainage: Concrete aprons adjacent to housing must drain efficiently to keep water from backing up under doors and wetting dwarf walls. Efficient and effective provision for channelling roof water away from housing
• Water collection and containment: Wash down water must be collected and disposed of away from housing and range as it poses a high risk to subsequent flocks. Where statutory C&D is required, all wash water has to be collected for disposal
• Single age sites: Sites with single buildings are easier to defend. Consider covered access where multiple houses are accessed from outside
• Single access points: Sites and housing should have single points of entry. Where multiple houses are on a single site, enclosed access should be considered to avoid necessity for external access. Step overs and biosecurity between houses are vital to protect the inner shell
• Rodents: Physically prevent access and ensure there are no harbourages near poultry units, follow BEIC and CRRU guidelines to prevent and control any populations

Site management (operational)

Having well-conceived sites and robustly constructed buildings are important for AI control but having the correct procedures and operational attitudes are vital.

The poultry industry understands biosecurity but struggles consistently to implement it at adequate levels.

The provision of on-site training that not only addresses the practical aspects but identifies and highlights individual responsibilities and the importance of good biosecurity to overall flock performance in the absence of AI is a key component of site operations.

Site operations

• Biosecurity policy: Each site must have one
• Make biosecurity measures accessible, easy to maintain, with regular training
• Have a named Biosecurity Officer for each site
• Record biosecurity breaches – why it happened and what you will do to stop it happening again
• Signage: Make it obvious and clear, and states what to do in different zones/areas
• Have a site access plan/site map: To show the dirty and clean areas
• Keep visitors to a minimum and get them to change clothes
• Have vehicle, visitor and staff records: That show movement on to site and between production units
• Wheel washing: Either automated or manual
• Terminal hygiene programme: This includes cleaning and disinfection, ensure foot dips, boot changes and stepovers are in place prior to disinfection. Record all chemical use and rates
• Unscheduled activity: Have a plan in place (e.g. equipment failure in the flock area and inhouse vaccination)
• Routine disinfection: Disinfectants and chemicals must be DAFM approved and used at the correct rates
• Have double step over barriers: Double step over zones (green, amber, red) with footwear changes and foot dips at each point
• Storage: Enrichments and bedding must be stored undercover and inaccessible to birds and animals
• Equipment: Tools and equipment must be cleaned and disinfected before being used in poultry areas, have dedicated tools for repair of equipment in flock space

Double set over entry

Summary

The predominance of H5N1 in the wild bird population makes the defence of the “inner shell” or flock the focus for biosecurity on farm. The distribution of wild bird faeces is unpredictable, however by having building structures that are sound, and necessary openings made inaccessible, the virus can be excluded from the flock space.

The virus therefore has to rely on us to walk it into the flock space where it is able to replicate rapidly. Simple yet effective biosecurity practice will deny the virus access to the flock and allow producers to concentrate on maximising the flocks’ egg producing potential and maintain viable, sustainable enterprises.

If you have any comments or questions, on AI or biosecurity in general, please do not hesitate to contact St David’s Poultry Team.