When stunning animals e.g. by CO2-stunningaversive reactions may be seen among the animalsas a reaction to the high concentration of CO2. To avoidthe aversive reactions animals can be pre-stunned beforebeing final-stunned and perhaps killed or slaughteredwhen stunned. Pre-stunning of animals may be performedwith a combination of gas for pre-stunning comprisingat least air and/or O2 together with CO2 e.g. in aconcentration below 40%, at least air and/or O2 togetherwith N2O, or at least air and/or O2 together with N2Oand CO2, where CO2 may bi in a concentration below40%. For larger animals such as pigs pre-stunning is performedfor less than 60 seconds. A stunning system maycomprise means for pre-stunning of animals before performinga final-stunning and may include gas storage forre-use of the pre-stunning gas.
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