High expansion nitrogen foam – an effective method of culling poultry?

This method should be made available for immediate deployment for disease control, according to a report from the UK government’s Animal Welfare Committee.

High expansion nitrogen foam could be considered equivalent or better than the use of other systems, especially those that used live handling, says the Animal Welfare Committee.

There are currently a range of culling methods that the Animal and Plant Health Agency and contractors have to humanely cull birds on infected premises. These include mechanical percussive devises, containerised gassing units and whole house gassing. Capacity for carbon dioxide-based whole house gassing has increased significantly and is currently the method of choice where it can be used effectively and deployed quickly. However, there are scenarios – such as when houses are not fully sealed, or supply issues – where this may not be the most effective option.

Using high expansion nitrogen foam has the potential to enhance the government’s ability to carry out mass depopulation in avian influenza-infected premises and other notifiable avian disease situations, providing an additional culling method suitable for naturally ventilated poultry buildings.

Conclusions following field trials

The study, which included field trails, made the following conclusions:

• The need for lengthy and expensive primary research on the use of high expansion nitrogen foam in species other than those already studied can be avoided as the anoxic effect of high expansion nitrogen can be expected to affect all poultry species in a similar way physiologically. All species will succumb at levels of oxygen below 1%, although some may take longer than others to lose consciousness.
• Preferred species and housing types for the application of high expansion nitrogen foam are litter-based broilers, broiler breeders, meat turkeys and meat ducks, because these have all been tested with the foam delivery system. Litter-based turkey breeders and duck breeders are also housed in a similar layout to broiler breeders. There is a need to do field trials using housing systems other than floor-based and with different species and ages of birds. Evidence is required on possible differential behavioural responses to the foam carrier depending on bird age or poultry species or type. Use of low lighting should be considered to reduce behavioural reactions.
• It is difficult to monitor welfare directly once birds are submerged in foam. Methods of monitoring behaviours and unconsciousness of birds in the foam are needed to ensure consistent application of the killing method across the flock. These include multiple gas monitors and camera systems, including infra-red in the dark, in each shed. Assessors should try and plan to extract a sample of birds in shorter time than seen in trials to access unconsciousness and death.
• A derogation from PATOK article 5 requirements pertaining to monitoring or visualisation of individual birds at the point of killing should be considered given confidence generated by the scientific studies on this method of killing poultry.
• Placing of foam generators in the shed to generate a broad foam “wave” from both ends is important to prevent birds gathering at edges or in corners and lowers the risk of smothering. Monitoring and adjustment of the bow wave of foam by the operators to ensure sufficient coverage of birds with foam throughout the kill is very important.
• Where depopulation is being undertaken for disease control, welfare harms associated with culling methods should be assessed against the welfare impact upon poultry infection and death.
• Low or medium expansion foam should not be used for culling poultry as they occlude the airway and cause death by hypoxia, which is equivalent to drowning or suffocating and is not recognised as humane under both domestic UK and EU legislation, nor the 2018 World Animal Health guidelines on the killing of animals for disease control purposes.