Technical note: Construction of a CO supply system for depopulation of pigs in a container

Situations may arise where authorities need to depopulate large quantities of pigs in a short time. This must be done in an animal welfare-responsible manner. This paper describes in detail a technical mobile container system for CO₂ depopulation of pigs. The system consists of simple and easily accessible materials and can be replicated and scaled for multiple container systems for CO₂ depopulation. The container system was tested at 4 depopulation events where the pigs' behavior was filmed (1 event) and the duration of the various procedures was recorded. The results showed that the system's capacity met AVMA's recommendations for a CO₂ supply rate of 10% to 30% of the chamber volume per min. On average, the containers were supplied with CO₂ for 7 min, and it was possible to maintain a CO₂ concentration of 80% for at least 10 min after stopping the CO₂ admission. By maintaining the tarpaulin on the container during transport, this "extending effect period" can be utilized for additional CO₂ exposure and acts as an extra safeguard for successful depopulation. Target CO₂ concentration of 80% occurred after a mean of 7 min. Pig escape attempts were first observed 2 min:26 s after the start of CO₂ exposure. Presumably due to the stocking density (a mean of 0.52 m² per pig), no loss of posture (indicating loss of consciousness) could be observed. On the other hand, the last escape attempts were observed after 3 min:04 s, and the last atactic movements after 3 min:13 s. It is therefore reasonable to assume that all pigs have lost consciousness around that time. No pigs survived the procedure, and the described CO₂ depopulation system therefore lived up to expectations. We recommend that users are given the opportunity to practice thoroughly before an authentic emergency.