Anoxia – Applying the technique

Anoxia technique

High expansion foam

The Anoxia technique is unique for creating an environment without oxygen under atmospheric circumstances. High expansion foam is produced by mixing nitrogen, a mixture of water and specially developed high expansion detergent. The expansion rate is upto 1:1000, meaning that 1 litre of water/foam agent mix expands up to 1 m3 foam. Due to the specially designed foam generator, the high expansion foam bubbles are filled with a > 99% concentration of nitrogen. Therefore, the oxygen level surrounding the animal drops from 21% in atmospheric air to < 1 % once the animal is submerged in the foam.

Convulsions, but no stress or pain

The animals need a constant supply of oxygen to the brain. Applying Anoxia foam, the oxygen is replaced by nitrogen. As a result the nitrogen level is raised to > 99% and the oxygen level is lowered to < 1%. Considering the natural reaction to sudden lack of oxygen the animal is rendering quickly into unconsciousness. As a consequence, behavioral indicators like loss of posture and convulsions will appear. With this in mind, unconscious animals are insensitive to perceive unpleasant sensations like pain.

How Anoxia foam is created

First of all, a mixture of 97% water and 3% high expansion foam agent is sprayed into the Anoxia foam generator, creating a thin film on the outlet of the generator. At the same time, nitrogen is added with overpressure into the foam generator. The nitrogen expands when it exits the generator. This creates a robust high expansion foam. The high expansion foam bubbles are filled with > 99% nitrogen.

Single foam generator systems

In practice, one Anoxia foam generator creates a volume of up to 750 liter of high expansion foam per minute. This volume is more than sufficient to fill a wheelie-bin container within 30 seconds. The most common container volumes are:


  • M size – 240 liter;
  • L size – 340 liter;
  • XL size – 370 liter

The choice of the volume of the container depends of the size of the animal and/or the number of animals that need to be stunned/killed. A lid with a chiffon seals the container. As soon as the foam exits the chiffon, the gas supply is stopped and the chiffon is closed. The nitrogen gas concentration in the container remains at 99%.




Anoxia: What is it?

An explanation of the anoxia principle

The Anoxia technique is developed as alternative for existing animal stunning methods that are based on the use of CO2, electrocution, neck dislocation, captive-bolt, as well as killing methods like de-bleeding and maceration.
In the past 10 years, Wageningen University and University of Glasgow conducted several studies that proved that the technique could be applied successfully for culling poultry (Proof of Principle Anoxia Technique). This was the start of the development of several applications based on the Anoxia principle, using high expansion foam filled with >99% Nitrogen.

The technique has now been introduced in:

    1. Stunning and killing of sick and cripple killing piglets less than 5 kg
    2. Stunning and killing of sick or cripple poultry (especially poultry > 3kg) who need to be killed on the farm by the staff for welfare purposes (avoiding unnecessary stress or pain)
    3. Stunning and killing of poultry that arrives on the slaughterhouse but that are unfit to be slaughtered (due to injuries occurred during transportation – providing signs of possible illness etc.)
    4. Stunning and killing of male pullets at the hatchery
    5. Stunning and killing of half-hatched chickens and embryos in partly-hatched eggs, before destruction
    6. Stunning and killing parent stock poultry
    7. Killing of animals that have been stunned (captive bolt – blow-on-the-head method, etc.) replacing killing by de-bleeding
    8. Culling of ex-layers
    9. Culling of poultry for disease control purposes


Last November 2016 the campaign started the launch of the commercialization of the Anoxia applications in Holland, Germany and Sweden, focusing on the areas where a solution is most needed: piglets (< 5kg) and poultry (> 3kg) on farms.




Dossier Stable Gassing: Scientific review on killing spent laying hens on the farm

Scientific review on killing spent laying hens on the farm. CO2 in a mobile container or stable gassing?

September 2015: In Sweden, spent laying hens are killed either by traditional slaughter; on-farm with CO2 in a mobile container combined with a grinder; or with CO2 stable gassing inside the barn. The number of hens killed using the latter method has increased. During these killings a veterinarian is required to be present and report to the Swedish Board of Agriculture.

Data were registered during four commercial killings and extracted from all official veterinary reports at CO2 whole-house killings in 2008–2010. On-farm monitoring showed that temperature decreased greatly and with high variability.

The time until birds became unconscious after coming into contact with the gas, based on time until loss of balance, was 3–5 min.

Animal welfare

Veterinary reports show that 1.5 million laying hens were killed, in 150 separate instances. The most common non-compliance with legislation was failure to notify the regional animal welfare authorities prior to the killings. Six out of 150 killings were defined as animal welfare failures, eg delivery of insufficient CO2 or failure to seal buildings to achieve adequate gas concentration. Eleven were either potentially or completely unacceptable from the perspective of animal welfare.

This study shows that there are grounds for concern regarding the latter. However, there remain several risks to animal welfare and increased knowledge would appear vital in order to limit mistakes related to miscalculations of house volume, improper sealing or premature ventilation turn-off.

There are aspects of animal welfare that should be taken into account: concerning the use of CO2 in the barn to euthanize spent method of killing itself, which have been studied extensively (e.g. Sandilands et al 2011; McKeegan et al 2012; Turner et al 2012); besides, the hazard to welfare when the method is performed on a larger scale, commercially, and the legislation or standard operating procedures for the euthanasia are not adhered to.


Dossier Anoxia Method: The sensible culling method for the use on organic farms

Organic poultry farming is the most responsively production system to produce healthy, good quality poultry meat and eggs in an ecologically way. It’s designed to avoid the need for agrochemicals and to minimize damage to the environment and wildlife.

Still, also organic poultry production is not free from the danger becoming infected by contagious diseases, like the current H5N2 outbreak in Canada and the USA.

All currently commercially available depopulation techniques focus on stamping out the virus, in an attempt to stop the spreading, not on maintaining animal welfare standards: methods like macerating birds alive; using CO2 in containers or throughout the entire poultry house; by electrocution; or by occlusion of the trachea with firefighting foam. This makes these techniques irreconcilable with the principle of organic farming, because the culling process with he current methods leave little room for the animal’s welfare rights in the last day of its existence.

Since June 2015, a new sensible culling technique is commercially available that serves both the goal to bring an outbreak to a stop and to maintain a high level of animal welfare during the process of culling for disease control purposes.

The Anoxia method is the most humane method to euthanize animals that are in severe pain or suffer severely seems to be the use of nitrogen gas foam. By this method the animals will be unconscious within a short time through an abundance of nitrogen. The animals die in a short time, without regaining consciousness.

The method of nitrogen gas foam uses a barrel, filled up with a layer of high expansion foam (big bubbles) completely filled with pure nitrogen. The animal will be placed in the foam and covered with a layer of foam of at least 60 centimetres. The animal will breathe 98 per cent nitrogen. The amount of oxygen in the blood diminishes very quickly and the animal will very soon be unconscious. Because of the extreme oxygen deficiency (anoxia) the animal dies within one and a half to two minutes. The animal will not regain consciousness and won’t notice that it dies.

The animal will be unaware that it breathes in pure nitrogen and it will not be harmful or painful for the animal because the normal air an animal breathes consists already of 78 per cent nitrogen. Inhalation of nitrogen is therefore not stressful, whereas for example with high concentrations of carbon dioxide the animal will try not to breathe.

The Anoxia method is not physically demanding on the farmer and his employees. The animals almost instantly lose consciousness after being dipped through the foam. Fixation of the animal to avoid them to hurt themselves during stunning is not needed, as necessary in most other methods. Because of the thick nitrogen foam layer and the amount of 98 per cent nitrogen it is certain that the animal will die. The chance that the method fails and the animal regain consciousness and won’t die, are next to zero.


Dossier Anoxia: N2GF equipment commercially available in Benelux and Germany

Marking March 31 2015 as the official launching date, the First series of Anoxia Foam systems that will be officially branded as N2GF equipment is now commercially available in Netherlands, Belgium and Germany.

Anoxia Foam is a new and promising technique to euthanize farm animals with less negative impact on animal welfare. This was the conclusion of the veterinarians participating in the first course on Anoxia technology that was held last February in Barneveld, Netherlands. The Anoxia Foam technique consists of stunning animals in nitrogen gas foam, causing loss of consciousness within 20 – 30 seconds without stress. Poultry vets from Netherlands, Belgium and Germany joined the training that was accredited by the Royal Dutch Society of Veterinary Science.

N2GF systems consist of a high-expansion foam nozzle, fed with nitrogen from a high-pressure gas cylinder or from a nitrogen generator that produces nitrogen on the spot. The nitrogen generator has been specifically designed for use in a poultry house atmosphere by Parker Hannifin, the world leading company in this area.

The N2GF systems are now launched by Anoxia Europe BV in the Netherlands, Belgium and Germany (Lower Saxony and Nord Rhine-Westphalia). Anoxia Europe will be coordinating development of the N2GF technique in consultation with veterinary authorities and will be sharing best practices across Europe. Certified veterinarians will support a proper use of the N2GF system to safeguard animal welfare, in implementation of the relevant EU Regulation 1099/2009.

40 complete N2GF systems will be tested in everyday practice on a variety of poultry farms for stunning and euthanizing of parent stock, turkeys, ducks, layers and broilers. For a special introductory offer, see

For more information contact Dr Michiel van Mil, Anoxia Europe, at or +31-3417016876


Dossier Taiwan: Reduction risks of spreading of infections during mass outbreaks

During the AI Symposium on managing outbreaks in Taiwan, the main subject was managing the outbreaks without breaching animal welfare during the culling operations. Although it seams impossible, this can be done using the Anoxia method (see also for more information), under the condition that the entire process is been taking into account: killing of animals, carcass disposal, transport & logistic, Occupational Health & Safety, environmental issues, pest control, contact between animals and humans: all these factors contribute to the risks of spreading. If one factor fails, the virus can escape and infect the next flock, making it needed to kill more birds. For that reason, all factors are equally important to maintain animal welfare during outbreak situations.

In a number of recently published studies, Professor Stegeman (University of Utrecht, Holland) explains that serologic spreading of viruses is related to human contacts with contaminated infected animals, carcasses, manure and materials infected/suspected animals; movements of farm labourers, products, equipment etc. Most of these contacts (and movements) take place prior, during, and after the culling procedure, whereas the quantity and the intensity of the contacts – thus this human contact/materials are decisive factors for the serologic spreading of viruses to enter farms and most likely play an important role in spreading between farms. Suspicion/infection of farm animals inevitably leads to preventive culling of all farm animals within the direct proximity. For that reason, the serologic spread of viruses has become a major animal welfare indicator that has to be taken into consideration as such.

Each culling procedure features its own unique contact pattern between animals and humans and is based on applied culling, disposal and transport technique. These contact patterns related to the specific combination of applied methods, defines the major contribution factors for spreading of infections. Therefore should the potential risks of these procedures be evaluated and rated on the art and the intensity of the potential contact between animals and humans/materials, prior, during and after the procedure.

Therefore, the entire procedure of killing, disposal and transportation is therefore considered as Major Interest, in terms of animal welfare.


Dossier H5N8: Wind-Borne Spread of Highly Pathogenic Avian Influenza Virus between Farms

The current outbreaks of H5N8 and H5N2 in Europe, North America and Asia it is important to implement high level bio security measures at farms to prevent production animals becoming infected. Once a farm is infected, culling entire flock is the only option to prevent further spreading with devastating consequences for the industry.

During the 2003 outbreaks of H7N7 in Holland the preferred culling technique was whole house gassing, also known as stable gassing.
Practical experience has shown that, in whole house gassing, the birds start to die after approximately 35 minutes and the entire operation ends after 2 to 3 hours. Killing by whole house gassing is most suited to large flocks in floor management systems. Under certain circumstances, it is possible to use whole house gassing in cage or aviary housing.
From the 1.100 farms that have been eradicated, stable gassing has been the technique of choice on 568 farms (51,6% of all farms), culling in total 21.740.000 birds (74,3% of all poultry). On 55 farms (10,7%), Carbon Monoxide (CO) has been used; on 513 farms (90,3%), Carbon Dioxide (CO2) was used.

Before the technique can be applied, the house must be well sealed. The screens and shuttering in an open house mean that it is also possible to make these houses gas-tight in order to carry out whole house gassing. The ventilation is switched off immediately before gassing.

The principle of stable gassing using CO2 is Hypoxia: displacement of atmospheric air by at least 70% , CO2 by volume. The gas is pumped into the house at high pressure and slowly fills the space. Stable gassing is a complicated technique to apply because it is difficult to measure whether the minimum concentration is achieved the animals can be stunned and killed and it is difficult to measure the concentration accurately. Therefore the total amount of gas that is pumped in resembles at least 2 to 3 time the volume of the house.
In order to fill the house with gas, the air in the house has to be replaced, exiting through any channel it can find. Most of the time, that is through ventilation at the top of the building or through cracks in the walls and the roof. The displaced air also causes (possibly) contaminated farm-dust particles and feathers deposited into the open air.

After the poultry is culled and before the dead birds can be collected safely, the house must be ventilated for approximately three hours to ensure rapid and complete removal of the gas from the house air. This ventilation also causes contaminated farm-dust particles from inside the house to deposit to the open air.
To understand the risks of spreading contaminated materials caused by stable gassing, a quantitative understanding of the spread of contaminated farm dust between locations is a prerequisite for obtaining much-needed insight into one of the possible mechanisms of disease spread between farms.

The researchers Amos Ssematimba, Thomas J. Hagenaars, Mart C. M. de Jong of the Dutch Department of Epidemiology, Crisis Organization and Diagnostics, Central Veterinary Institute (CVI) part of Wageningen University and Research Centre, Lelystad, The Netherlands, and Quantitative Veterinary Epidemiology, Department of Animal Sciences, Wageningen University, Wageningen, The Netherland developed a model to calculate the quantity of contaminated farm-dust particles deposited at various locations downwind of a source farm and apply the model to assess the possible contribution of the wind-borne route to the transmission of Highly Pathogenic Avian Influenza virus (HPAI) during the 2003 epidemic in the Netherlands.

The model is obtained from a Gaussian Plume Model by incorporating the dust deposition process, pathogen decay, and a model for the infection process on exposed farms. Using poultry- and avian influenza-specific parameter values we calculate the distance-dependent probability of between-farm transmission by this route. A comparison between the transmission risk pattern predicted by the model and the pattern observed during the 2003 epidemic reveals that the wind-borne route alone is insufficient to explain the observations although it could contribute substantially to the spread over short distance ranges, for example, explaining 24% of the transmission over distances up to 25 km.


Anoxia presentation Australia

This is the 3th presentation of a series of documents, presented during the conference on the application of the Anoxia method for euthanizing animals.

The conference is held in Canberra (Australia) on February 21, 2014. The conference is organized for representatives of animal welfare organizations, Australian animal health authorities and the industry and gives an overview of more scientific based information on the Anoxia method.


Creating Nitrogen on location: important new animal welfare application

This is the second presentation of a series of documents, presented during the conference on the application of the Anoxia method for euthanizing animals.

The conference is held in Canberra (Australia) on February 21, 2014. The conference is organized for representatives of animal welfare organizations, Australian animal health authorities and the industry gives a general overview of the Anoxia technique.


From Ausvet plan to implementation

This is the 1st presentation of a series of documents, presented during the conference on the application of the Anoxia method for euthanizing animals. The conference is held in Canberra (Australia) on February 21, 2014. The conference is organized for representatives of animal welfare organizations, Australian animal health authorities and the industry and gives an overview of some important practical issues related to Emergency Response, based on my experiences during the outbreak of H7N7 in Holland.