There has been concern about the stress involved in loading pigs into CO2 stunning units. Present systems suffer from the innate problem that it is a “stop-go” procedure. Therefore, studies were required to test alternative systems for improving loading of pigs into CO2 units and reduce distress caused to the animals.

The four alternative systems for loading pigs into CO2 stunning units tested in the lairage of a commercial plant on 1600 slaughter pigs were as follows:

• 1) Semicircular loading pen - direct individual feeding into a simulated CO2 entrance;

• 2) Semicircular loading pen - feeding individuals into a simulated CO2 entrance through a single file race;

• 3) Semicircular loading pen - feeding animals into a twin race ending with a flap gate allowing exit of one animal at a time;

• 4) Loading pen (no swing gate) and a twin race ending with a flap gate allowing single exit.

Considering that most CO2 handling systems have to restrict entry of pigs into units, both restricted and unrestricted entry to the simulated gas unit was tested in our evaluation.