Gas mixtures for anaesthesia and euthanasia in broiler chickens

The aim of this experiment was to develop an alternative, acceptable and hu mane method for killing broiler chickens. Our main premise was that euthana sia should preferably take place in two steps. Firstly, the bird should be anaesthetised quickly and completely using appropriate procedures and, seco ndly, the anaesthetised bird should be killed as quickly as possible. Two g as mixtures were considered for anaesthesia: 40% carbon dioxide with 30% ox ygen and 30% nitrogen or 40% carbon dioxide with 15% oxygen and 45% nitroge n. It was found that the birds' behaviour in the high oxygen environment wa s less disturbed, with less agitation and distress being demonstrated. For this reason, the high oxygen condition is to be preferred and this anaesthe tic was used in the second part of the experiment. The bird was exposed for one minute to 40% carbon dioxide, 30% oxygen and 30% nitrogen (anaesthesia ) and then to 80% carbon dioxide, 5% oxygen and 15% nitrogen (euthanasia). This condition was compared with the frequently used euthanasia condition i nvolving argon. The use of argon is based on the idea that it produces fast suffocation of the birds. The argon condition consisted of 30% carbon diox ide and 60% argon in air with less than 2% oxygen and 8% nitrogen. The chic kens died significantly later in the oxygen/carbon dioxide condition than i n the argon condition. Judgements of death were based on both the pattern o f electrical brain activity and on heart rate. The time taken for the chick ens to become unconscious, as judged from the isolectric electroencephalogr am, was also significantly longer in the oxygen/carbon dioxide condition th an in the argon condition. However, in the argon condition the birds immedi ately showed strong signs of agitation and distress, particularly intense a nd heavy muscle contractions, whereas these signs were less pronounced in t he oxygen/carbon dioxide condition. It is concluded that, although the chic kens lost consciousness sooner and also died sooner in the argon condition, there are good reasons to prefer the oxygen/carbon dioxide condition becau se it results in less disturbed behaviour and the birds exhibited milder si gns of distress during the period when consciousness cannot be fully exclud ed. Hence, a milder death, taking somewhat longer, is preferred to a quicke r but more distressing death. Finally, the oxygen/carbon dioxide condition was repeated with turkeys when, in general, the results were the same.