CO2 stunning is the dominant method for pig slaughter in the UK and EU but is highly aversive — pigs show strong escape attempts and distress during exposure — with viable alternatives now available.
Pigs entering CO2 gondolas experience 20-30 seconds of acute distress from hypercapnia (elevated CO2) before losing consciousness. During this period, pigs show vigorous escape attempts, vocalise, and exhibit signs of extreme distress that are observable at abattoirs with gondola windows. The welfare cost is experienced by every pig slaughtered in these systems globally — billions annually. Alternative inert gas or low CO2/argon mixtures achieve rapid loss of consciousness without the aversive response. The technology exists; adoption requires regulatory change and industry investment.