- - news, features and articles for the meat processing industry

Featured Articles

Multi-stage Carbon Dioxide Gas Stunning of Broilers

03 May 2013

New research from the Netherlands indicates that a method involving several stages of carbon dioxide can offer reliable and effective stunning.

The five-stage treatment they used was preferable to a four-stage process, which carried a higher risk of convulsions and possible injuries.

In a paper published recently in Poultry Science, Marien Gerritzen of Wageningen UR Livestock Research in the Netherlands and co-authors there and with Meyn Food Processing Technology BV report that the stunning quality of animals for slaughter remains under constant scrutiny.

In response to previous research showing low stunning efficiency in poultry, the conventional water bath will be phased out in the Netherlands. Presently, the main practical alternative to water bath stunning of poultry is a two-phase gas stunning method. Gas stunning methods are recognised by governments and animal welfare organisations across Europe.

The Dutch group conducted three sets of experiments on gas stunning methods using carbon dioxide in two phases. Two methods were examined to identify potential effects on bird behaviour and investigate their practical implications:

  • a five-stage incremental carbon dioxide scheme lasting six minutes (treatment 1) and
  • a four-stage incremental carbon dioxide scheme lasting four minutes (treatment 2).

The onset and duration of unconsciousness were specifically tested in experiment 2 by using 25 birds equipped with electrodes monitoring brain and heart activity. Behavioural responses were observed on 15 non-instrument-monitored birds kept in the same cages at that time.

Results in all three sets of the experiments showed that multi-stage gas stunning was stable and consistent, and increases in carbon dioxide concentrations were rapid and reliable. Ambient temperatures and relative humidity of the air remained within acceptable levels at all times.

Induction of unconsciousness occurred below 40 per cent carbon dioxide and did not significantly differ between treatments.

Conscious birds were never exposed to high carbon dioxide concentrations (>40 per cent carbon dioxide) yet some birds showed signs of distress, e.g. head shaking, wing flapping, before losing consciousness.

Discomfort experienced during exposure to low (<40 per cent) carbon dioxide concentrations compares favourably with the experiences of handling, tilting and or shackling of conscious birds when using alternative stunning methods, implying that multi-stage gas stunning has distinct advantages for bird welfare.

Compared with the multi-bird water bath system, Gerritzen and co-authors concluded that this method provides an opportunity to guarantee that all birds are properly stunned. The risk of convulsions, which was higher with treatment 2, leading to possible injuries, indicates a preference for the five-stage treatment.


Gerritzen M.A., H.G.M. Reimert, V.A. Hindle, M.T.W. Verhoeven and W.B. Veerkamp. 2013. Multistage carbon dioxide gas stunning of broilers. Poult. Sci. 92(1):41-50. doi: 10.3382/ps.2012-02551

Further Reading

You can view the full report (fee payable) by clicking here.

March 2013

Our Sponsors


Seasonal Picks

Meat Cuts and Muscle Foods - 2nd Edition