Stunning pigs with different gas mixtures: gas stability
The stability and uniformity of the following gas mixtures: 90% argon; 85% argon and 15% carbon dioxide (CO2); 70% argon and 30% CO2; 98% nitrogen (N2); 92% N2 and 8% CO2; 90% N2 and 10% CO2; 85% N2
and 15% CO2; 80% N2 and 20% CO2; 70% N2 and 30% CO2; and 90% CO2 by volume in atmospheric air were assessed in a commercial dip-lift stunning system when the cradle was either stationary or in motion. The gas mixtures of 90%
argon, 85% argon and 15% CO2, 70% argon and 30% CO2, 85% N2 and 15% CO2, 80% N2 and 20% CO2, 70% N2 and 30% CO2 and 90% CO2 by volume in atmospheric air could be sustained in a commercial dip-lift
stunning system. The stability of the gas mixtures 92% N2 and 8% CO2, and 90% N2 and 10% CO2 by volume in atmospheric air were lower than in the previous cases. On the other hand, an N2 concentration higher than 94% by volume in atmospheric
air could not be sustained in the stunning system. In addition, gas mixtures of argon and CO2 showed a higher stability than gas mixtures of N2 and CO2. The uniformity at different levels inside the pit (defined as the capacity of the gas to maintain its concentration
constant at different levels inside the pit) was higher in 90% argon, or argon and CO2 mixtures and N2 and CO2 mixtures than in 90% CO2. This fact ensures that for the whole time the animals are inside the pit, the same conditions are applied, which
is not the case for 90% CO2.