October 25 2017 CO2 stunning in transport container favorable for animal welfare

Figure 1: Three double-container CAS units with de stacker (Left)

Authors: J. Bergsma, W. Veerkamp and M. Bettonvil, Meyn Food Processing Technology B.V., Oostzaan, The Netherlands

Pre-slaughter distress is predominantly caused by live tilting and shackling of fully conscious birds, which is considered a major animal welfare issue in the stunning process (Gerritzen et al, 2011). Controlled Atmosphere Stunning (CAS) of birds in their transport containers eliminates live handling and can reduce pre-slaughter stress (Grandin, 2013).

After research, Meyn and Praxair developed a batch-wise Multistage CO2 stunning system where the CO2 concentration is gradually increased by a stepwise program. The program is designed, aiming for an irreversible stun performed in a humane way, which is effective for a wide variety of birds.

Results and Discussion

Controlled experiments with different CO2 concentrations and exposure times were performed in cooperation with Wageningen UR Livestock Research (WUR LR). A 5-stage program and a 4-stage program were evaluated in detail (see table 1).  During the first stages of the programs, the CO2 concentration is gradually increased to reach a controlled stun in the first phase (<40% CO2). In the second phase (>40% CO2), the CO2 concentration is increased to levels were hypoxia results in an irreversible stun. Research and experience showed that the behavioral and physical reaction of the birds during insensibility induction is effected by CO2 concentration and exposure time.

The 4-stage program led to more signs of convulsions compared to the 5-stage program. The 5-stage program is implemented in the Meyn Multistage CO2 stunning system since 2012.

Table 1: Behavioral and physical reactions of birds during CO2 stunning with 2 different programs.

 The stunning program is effective and no behavioral difference has been observed between breeds, free range and weight of the birds within several countries with different climates (see figure 2 and table 2).   Specific behavior during insensibility induction is headshaking, deep breathing and or gasping followed by loss of posture, short intermediate wing flapping, and mild convulsions.

 Figure 2: Countries in Europe with Meyn Multistage CO2 stunning systems.                                                        Table 2: Specifications of operational Meyn CAS systems



• A humane stun with CO2 should be performed with a gradual and controlled increase of CO2 in a controlled environment in the bird’s transport crates.

• The Meyn Multistage CO2 stunning cycle is effective for a wide range of birds, breeds and growing conditions among a wide variety of weight ranges in various climates in different countries.

• Animal welfare experts conclude that the slight discomfort experienced during this CAS is to be preferred to the stress caused by handling conscious birds.   References Gerritzen, M.A. et al (2011) Multistage gas stunning of broilers in transport containers, WUR Livestock Research, Poster. 

*This article was originally published in Meyn WORLD Magazine, click here to read the publication online.  


Gerritzen, M.A. et al (2011) Multistage gas stunning of broilers in transport containers, WUR Livestock Research, Poster
Gerritzen, M.A. et al (2012) Multistage gas stunning of broilers in transport containers with carbon dioxide in two phases, WUR Livestock Research confidential report nr 307 Grandin (2013):
Maxwell, M.H. et al (1990) Haematological and morphological responses of broiler chicks to hypoxia, Avian Pathology, 19:1, 23-40, DOI: 10.1080/03079459008418653


Interested in knowing more about Meyn's Multistage C02 stunning system?

Robbert Birkhoff 

T +31 (0)20 2045 468



Robert Bertens

T +1 770 967 0532


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