This document was presented at the Nordic Poultry conference in Reykjavik in November 2009, before the Anoxia method was commercially available. Dr. Berg compares in this document different methods of emergency killing of poultry, applicable within the Nordic poultry industry (Sweden, Norway, Denmark, Finland and Iceland).

1. Nordic Poultry Conference, Reykjavik, Nov 17th
20th
2009
On farm killing of poultry for disease control and other emergencies
C. Berg
Department of Animal Environment and Health, Swedish University of Agricultural Sciences, PO Box 234,
SE 532 23 Skara, Sweden
Introduction
Poultry producers are generally well accustomed to killing a limited number of sick, underweight or
injured birds on the farm during each production period. Furthermore, in some Nordic countries the
killing of spent hens on farm is seen as an alternative to sending the birds off for slaughter. This is the
case especially if the farm is located far away from the nearest slaughterhouse, if birds are unfit for
consumption or if it is otherwise considered beneficial from an animal welfare point of view to avoid
crating and transporting the birds. In such cases, birds are often killed in house using carbon dioxide.
Flocks can also be killed using carbon dioxide in so called flow containers placed right outside the
building.
These situations, however, are for many reasons quite different from the situation that arises when a
flock is diagnosed with a contagious zoonotic or epizootic disease causing a request for immediate
destruction of the flock in question and possibly also other flocks on the premises, depending on the
nature of the disease.
Descriptions of various methods for on farm killing can be found in the literature (Berg, 2007; Berg et al.,
2007, Gerritzen et al., 2006, Raj, 2008; Raj et al., 2006; 2008). For small flocks at hobby level, methods
such as a blow to the head, electrical stunning or captive bolt stunning, all followed by neck dislocation
or bleeding (the latter usually discouraged for biosecurity reasons) or injection of barbiturates are often
recommended. For commercial flocks, however, these methods would be extremely time consuming
and also result in closer contact between infected birds and humans than desired from an occupational
hazards point of view. Although the capacity of some versions of containerized gassing systems using
carbon dioxide and/or argon gas would be reasonable, there would still remain a need to manually catch
and handle the birds. In order to avoid this, the method of choice during a disease outbreak is
whenever possible instead to kill the birds inside the house.
In house killing of laying hens, broilers and turkeys
As mentioned above, whole house killing of spent hens using carbon dioxide gas is a method which has
been used for several years, especially in Sweden where approximately 50 flocks of end of lay hens are
killed this way every year. This means that the method is listed with detailed provisions in the
legislation (Anon., 2007) and that both the gas supplying company and the practicing veterinarians are
now reasonably experienced in handling the method. Furthermore, Swedish legislation requires all
recently constructed laying hen, broiler and turkey barns to have a gas inlet pipe mounted already
during construction, in case of a disease outbreak occurring later.

2. Practical evidence from these killings show that calculating for 80 % CO2 to be used will result in final in
house levels of CO2 high enough to safely kill all birds within reasonable time and also allowing for some
gas leakage (Berg, in prep.). Buildings are sealed properly, but some openings are left in or near the
ceiling, to allow for air to escape thereby avoiding over pressurizing the building. A relatively narrow
pipe inlet is used, fitting a hose of approx 4 cm diameter. The cold gas will then enter the building at
high pressure and immediately evaporate and spread in the building. To avoid problems with birds
becoming hit by the cold high pressure gas jet, correct positioning of the inlet and the use of proper
barriers is crucial (Berg and Yngvesson, 2007).
The same method can of course be used when killing flocks for disease control purposes. It has been
shown to work well for both loose housed layers, caged layers (three tier systems), broiler and turkeys
in disease control situations. It should be acknowledged that carbon dioxide is considered moderately
aversive for poultry and will cause respiratory discomfort (Coenen et al., 2009), but this disadvantage
has to be evaluated in the perspective of the advantages related to process speed, availability,
biosecurity, workers’ safety and so on. Furthermore, carbon dioxide is currently used for stunning
broilers and turkeys at a considerable number of slaughterhouses throughout Europe (Coenen et al.,
2009, Hänsch et al., 2009). Recent research indicates that using inert gases, such as argon or nitrogen,
may not be as beneficial from a bird welfare perspective as previously thought (Coenen et al., 2009;
McKeegan et al, 2007). In Denmark, nitrogen gas has been used in trials for in house killing of laying
hens, with satisfactory results. Nitrogen can be used also for turkeys.
There are on going trials in other European countries looking at developing systems of distributing a
lethal gas by using gas filled foam (Gerritzen and Sparrey, 2008). However, no such method is currently
commercially available. In the US, standard fire fighting foam is used to suffocate the birds when killing
broiler and turkey flocks for disease control purposes (Benson et al., 2007). In Europe, this method is not
considered acceptable from an animal welfare point of view.
In house killing of ducks and geese
As stated above, using carbon dioxide works well not only for killing hens but also for turkeys. In theory,
carbon dioxide is lethal also to ducks and geese, and this effect has been demonstrated under
experimental conditions, at least for ducks (Gerritzen et al., 2006; 2007). However, practical experience
from countries having killed large numbers of geese and also ducks due to AI infection indicates that due
to the commonly used design of buildings for these species it is very difficult to arrange such whole
house killings in practice. Furthermore, also when killing these birds in containers using CO2, there are
reports indicating that the process is too slow to be acceptable from an animal welfare point of view,
even if all birds will eventually die.
Hence, there has been an interest in developing suitable methods for killing ducks and geese on farm.
For small numbers of birds, a swift blow to the head followed by neck dislocation is one possibility;
injection of barbiturates another. For large flocks, however, these methods are slow and require large
numbers of staff. In any case there are situations where in house killing is definitely to be preferred, for

3. biosecurity reasons. In the Scandinavian countries, duck and goose sheds are often reasonably stable
buildings, where sealing should not be impossible. To evaluate if using nitrogen would be suitable for
these species, a number of trials have been carried out.
The nitrogen project trials
The project, which was founded by the Nordic Council and coordinated by the Danish Ministry of Food,
Agriculture and Fisheries (Fødevarestyrelsen), covered on farm killing of turkeys, ducks and geese.
During the experimental phase, a number of birds were placed in Perspex test boxes, which were then
gradually filled with nitrogen until the level of residual oxygen was equal to or below 2 %. The gas
concentration, temperature and the behavioural reactions of the birds were continuously recorded.
During the on farm phase, empty commercial houses for ducks, geese and turkeys were used. A number
of birds were placed in the respective houses, which had been meticulously sealed, and nitrogen was
brought into the buildings via a number of hoses and left to evaporate. Afterwards, birds killed using
nitrogen and a number of control birds killed using barbiturates underwent postmortem examinations.
The project is now in the finishing phase, results are being analyzed and video footage is being
processed. One thing learned from these studies is the importance of developing practical methods for
guiding and controlling the nitrogen infusion and vaporization also in very large buildings, to ensure that
the oxygen level is rapidly and evenly decreased to desired levels. Furthermore, proper sealing is crucial.
Summary
There is substantial practical evidence showing that carbon dioxide gas can be used for killing hens,
broilers and turkeys in house on farm, in a way that can be considered acceptable from an animal
welfare point of view. Also nitrogen gas has been used for killing laying hens in house. The results from
the trials described above indicate that nitrogen gas can also be used for killing geese, ducks and turkeys
in house, provided that sealing is carefully carried out and that the gas can be evenly distributed in the
building.
References
Anonymous, 2007. Statens jordbruksverks föreskrifter och allmänna råd (SJVFS 2007:77) om
slakt och annan avlivning av djur, Saknr L22, 8 kap 19 § (legal text).
Benson, E., Malone, G.W., Alphin, R.L., Dawson, M.D., Pope, C.R. & van Wicklen, G.L., 2007.
Foam based mass emergency depopulation of floor reared meat type poultry operations.
Poultry Science 86:219 224.

4. Berg, C., 2007. Emergency killing of poultry during disease outbreaks in the Nordic countries.
Proceedings XIII International Congress in Animal Hygiene, Tartu, Estonia, ISBN 978 9949 426
32 4, pp 1053 1059.
Berg, C., Yngvesson, J., 2007. Avlivning av värphöns i stallet med koldioxid. Fjäderfä nr 7/07, 18
20.
Berg, C., Algers, B., Atkinson, S., Dzieciolowski, T., Björnerot, L., 2007. Akut avlivning av
fjäderfäflockar vid sjukdomsutbrott. Svensk Veterinärtidning, vol 59, 7:11 19.
Coenen, AML., Lankhaar, J., Lowe, JC., McKeegan, DEF., 2009. Remote monitoring of
electroencephalogram, electrocardiogram, and behaviour during controllled atmosphere
stunning in broilers: implications for welfare. Poult. Sci. 88: 10 19.
Gerritzen, MA, Lambooij, E., Stegeman, JA., Spruijt, BM., 2006. Slaughter of poultry during the
epidemic of avian influenza in the Netherlands in 2003. Vet. Rec, 159: 39 42.
Gerritzen, M., Lambooij, B., Reimert, H., Stegeman, A., Spruijt, B., 2007. A note on behaviour of
poultry exposed to increasing carbon dioxide concentrations. Appl. Anim. Behav. Sci., 108: 179
185.
Gerritzen, MA and Sparrey, J., 2008. A pilot study to assess whether high expansion CO2
enriched foam is acceptable for on farm emergency killing of poultry. Anim Welfare, 17: 285
288.
Hänsch, F., Nowak, B., Hartung, J., 2009. Evaluation of a gas stunning equipment used for
turkeys under slaughterhouse conditions. Livest. Sci. 124: 248 254.
McKeegan, DEF., Abeyesinghe, SM., MLeman, MA., Lowe, JC., Demmers, TGM, White, RP.,
Kranen, RW., van Bemmel, H., Lankhaar, JAC., Wathes, C., 2007. Controlled atmosphere
stunning of broiler chickens. II. Effects on behaviour, physiology and meat quality in a
commercial processing plant. Bri. Poult. Sci., 48 (4): 430 442.
Raj, M., 2008. Humane killing of nonhuman animals for disease control purposes. Journal of
Applied Animal Welfare Science, 11:112 124.
Raj, A.M.M., Sandilands, V. & Sparks, N.H., 2006. Review of gaseous methods of killing poultry
for disease control purposes. Veterinary Record, 159: 229 235.
Raj, M., O’Callaghan, M., Thompson, K., Beckett, D., Morrish, I., Love, A., Hickman, G. &
Howson, S., 2008. Large scale killing of poultry species on farm during outbreaks of disease:
evaluation and development of a humane containerized gas killing system. World’s Poultry
Science Journal, 64: 227 243.