Currently 85% of pigs in Australian abattoirs are being processed using a technique called CO2 stunning. This is intended to be a humane process, where groups of animals are exposed to high levels (<80%) CO2, designed to render the animal’s unconscious prior to being killed. However according to the RSPCA in reality this process is very rarely humane with many of the animals needlessly suffering prior to eventually becoming unconscious. The RSPCA website explains this in more detail on their website; https://kb.rspca.org.au/knowledge-base/is-carbon-dioxide-stunning-of-pigs-humane/

If you think about it, you don’t have to be a scientist or do a study to see this could easily be the case. Anyone who has flown on a plane would have seen the safety demonstrations telling us if the oxygen mask falls from overhead we must put it on immediately, and not wait to feel light headed before acting. This is because respiratory distress and the urge to take a breath is triggered by the build-up of CO2 in our bodies, not a lack of oxygen. If there is no oxygen in the air we breathe, our bodies cannot produce CO2 and respiratory distress or the urge to take a breath is not triggered. You fall unconscious possibly without even knowing which is why they say to act immediately. This is a vast oversimplification but it does help us to understand how studies commenting on the negative sides of CO2 stunning could be accurate.  

I used to believe that when it came to abattoirs and where my food came from "ignorance is bliss" was the best policy, or more accurately that the government would cater for the animal’s interest and ensure they were properly treated so I didn’t have to. However, I now feel this was a naïve and even an irresponsible attitude to adopt, since I now know more could be done to ensure the animals providing us with food are better treated.  

A change in the industry would not be as difficult as some may think. There are in fact simple measures that could be taken to virtually eliminate the distress caused to the animals and that is simply by changing the gas used. Swapping to another inert gas mixture, such as argon, nitrogen, or nitrous oxide, would not cause the same respiratory distress to render the animals unconscious. The RSPCA would like to see abattoirs move away from the use of CO2 stunning in favor of another inert gas and I feel we could do more to support them with this process and encourage the government regulatory bodies to make this a happen.  

Photo from "The Spruse"