Raj A B, Johnson S P, Wotton S B, McInstry J L
Department of Clinical Veterinary Science, University of Bristol, Langford, UK.
Vet J. 1997 May;153(3):329-39. doi: 10.1016/s1090-0233(97)80067-6.
Changes in the spontaneous electrocorticogram (ECoG) and somatosensory evoked potentials (SEPs) were recorded in 12 pigs in each of three gas killing treatments. The treatments were 90% argon in air with 2% residual oxygen; a mixture of 30% carbon dioxide and 60% argon in air with 2% residual oxygen; or 80-90% carbon dioxide in air. The mean times to loss of SEPs were 15, 17 and 21 s, respectively. The mean time to loss of SEPs recorded during killing with a high concentration of carbon dioxide was significantly longer than those recorded for the other two gas killing treatments (P < 0.05). Slow waves (high amplitude and low frequency) appeared on average 15 s after exposure to argon. In some pigs killed with the carbon dioxide-argon mixture, a decrease in the frequency of electrical activity was apparent, although slow waves did not appear during killing with a higher concentration of carbon dioxide. A suppressed ECoG (reduction in amplitude of signals) was recorded at 22 and 20 s respectively, during exposure to the carbon dioxide-argon mixture and 80-90% carbon dioxide in air, but the onset of ECoG suppression could not be determined exactly during exposure to 90% argon in air. The time to onset of an isoelectric ECoG was 54, 39d and 32 s after exposure to argon, carbon dioxide-argon mixture and a high concentration of carbon dioxide, respectively. The mean time to the onset of an isoelectric ECoG during exposure to argon was significantly longer than that recorded for the other two gas killing treatments (P < 0.05). Based on the time to loss of SEPs, it is concluded that during killing with a high concentration of carbon dioxide, pigs would have to endure a moderate to severe respiratory distress induced with this gas for a considerable period of time prior to the loss of brain responsiveness. Argon-induced anoxia appears to be the first choice from a welfare point of view for killing pigs, based on its lack of aversive properties and its effectiveness in rapidly abolishing brain responsiveness. A mixture of 30% carbon dioxide and 60% argon in air is considered to be more humane than using a high concentration of carbon dioxide, as the time to loss of brain responsiveness is similar to that using 90% argon in air.
在三种气体致昏处理中，每种处理的12头猪记录了自发脑电图（ECoG）和体感诱发电位（SEP）的变化。处理方式分别为：空气中90%氩气加2%残余氧气；空气中30%二氧化碳和60%氩气的混合物加2%残余氧气；或空气中80 - 90%二氧化碳。SEP消失的平均时间分别为15秒、17秒和21秒。高浓度二氧化碳致昏过程中记录到的SEP消失平均时间显著长于其他两种气体致昏处理（P < 0.05）。暴露于氩气后平均15秒出现慢波（高振幅和低频率）。在用二氧化碳 - 氩气混合物致昏的一些猪中，电活动频率明显下降，尽管在高浓度二氧化碳致昏过程中未出现慢波。在暴露于二氧化碳 - 氩气混合物和空气中80 - 90%二氧化碳时，分别在22秒和20秒记录到ECoG抑制（信号振幅降低），但在暴露于空气中90%氩气时无法准确确定ECoG抑制的起始时间。暴露于氩气、二氧化碳 - 氩气混合物和高浓度二氧化碳后，ECoG等电位的起始时间分别为54秒、39秒和32秒。暴露于氩气期间ECoG等电位起始的平均时间显著长于其他两种气体致昏处理（P < 0.05）。基于SEP消失时间得出结论，在高浓度二氧化碳致昏过程中，猪在脑反应性丧失之前，必须在相当长一段时间内忍受这种气体引起的中度至重度呼吸窘迫。从福利角度来看，基于氩气缺乏厌恶特性且能迅速消除脑反应性，氩气诱导的缺氧似乎是猪致昏的首选。空气中30%二氧化碳和60%氩气的混合物被认为比使用高浓度二氧化碳更人道，因为脑反应性丧失的时间与使用空气中90%氩气相似。
