CO2 Monitoring in Poultry and Pig Processing

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There has been more concern for increasing animal welfare standards in the meat processing industry over recent years. Not just an animal’s diet and living conditions but also the slaughtering procedures and process. A European Union rule1 states that every animal is stunned before slaughter to ensure that an animal cannot feel pain while being slaughtered.

One exception for animals killed at slaughterhouses is in a manner in keeping with religious rites. Numerous techniques can be utilized to render the animal unconscious, including mechanical stunning, electrical stunning, or through the use of gas.

Gas Stunning

Also known as controlled atmospheric stunning, gas stunning requires utilizing an environment with a high carbon dioxide (CO2) concentration to render the animal unconscious. It can also be employed as a way of killing the animals directly.

This method of stunning is becoming increasingly popular, especially by Europeans, because it offers a reduced risk of injury through the stunning process. This is because there is no need to restrain the animals beforehand, this can also raise the meat quality, and is largely considered to be one of the most humane stunning methods.2

The slaughter of animals may also be necessary for farmers as part of livestock culls when there is an outbreak of diseases which are highly contagious. The foot-and-mouth disease outbreak in the UK in 2001 triggered mass culls of millions of livestock.3 Usually, when livestock culls are imposed to stop the spread of disease, they are paired with limitations of the movement of livestock, which includes sending them to slaughterhouses.

Criticality of CO2 Concentrations

It is critical to use the correct CO2 concentrations for gas stunning or slaughter to cause minimum harm to the welfare of the animals. Incorrect concentrations of CO2 results in the livestock remaining conscious and alert. Pigs have been reported to show some signs of distress4 if the CO2 amount is too high relative to the O2 amount at the start of the process.

So, there are strict rules about the concentration levels of CO2 that should be used and it is also obligatory that the environmental monitors used are able to accurately and reliably measure such concentrations to protect the welfare of these animals.

For pigs and other herd animals, a number of animals are kept together in a chamber where the atmospheric gas combination is quickly altered to one appropriate for stunning them. A similar method can be used for poultry and other animals.

The Welfare of Animals (Slaughter or Killing) Regulations 1995 (WASK 95)5 in the UK, specifically covers the gas mixtures that can be used for these purposes. It states that the carbon dioxide concentration must be less than 30%, and devices must be employed to measure the maximum concentration by volume, with warning systems that sound if concentrations stray from the legislated limits.

Animal Processing and Edinburgh Sensors

Edinburgh Sensors, have a variety of devices well-suited for CO2 sensing for livestock stunning and slaughter, with their line of real-time gas monitors. The Guardian6 and GasCard7 real-time monitors give highly precise, online sensing capability for CO2 with real-time data recording and the ability to integrate the sensors with alarms or other gas-monitoring sensors as needed.

The Guardian NG series utilizes infra-red detection to give a CO2 detection range of 0 – 100 % volume and 0 – 3000 ppm. There are two alarm relays, plus an alarm that can be calibrated to any point of the detection range. This can be employed to control further devices, for example in the case of gas slaughter, it could be utilized to give the optimum gas mixtures by varying the gas concentrations as required.

The on-screen device can be used either to monitor concentrations or to set-up the device, which has an initial warm-up time of just one minute. The device’s response time is low enough (less than 30 seconds from the sample inlet) that it is appropriate for the time-critical nature of detecting gas concentrations in the stunning process, which is important because the legislation states exactly how long livestock remain under certain atmospheric conditions.

As the Guardian NG series can detect gases from sampling points up to 30 meters away by using their integral sampling system, the monitors can be mounted on the walls of the chamber where the livestock will be kept. All systems also come with the full technical and user support.

Dr. Martin Wenzlawowics, Head of “BSI Schwarzenbek” for applied animal welfare at transport and slaughter has recommended and encouraged the use of the Guardian NG series for this specific application. With 2% accuracy across the full range of detection, the device is also very robust as measurements are unaffected by 0 – 95% relative humidity.

References and Further Reading

  1. Slaughter and Stunning,, (accessed August 2018)
  2. C. Berg, M. Raj, Animals, 2015, 5, 1207-1219
  3. FMD Data Archive, (accessed August 2018)
  4. Report, Stunning of slaughter pigs with CO2. A pilot research to the effect of adding O2 to a CO2 concentration on animal welfare,, (accessed August 2018)
  5. WKA Regulations,, (accessed August 2018)
  6. The Guardian NG,, (accessed August 2018)
  7. The GasCard,, (accessed August 2018)

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.

For more information on this source, please visit Edinburgh Sensors.


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