This study investigated how the carbon dioxide (CO2) concentration within a chamber affects the efficacy of CO2 euthanasia and how the efficacy of CO2 induction methods changes as birds age. In experiment 1, pairs of broiler chicks (n = 192; 0, 3, and 6 D of age) were immersed into a chamber prefilled with 70, 80, 90, or 100% CO2. For experiment 2, 3- and 6-day-old broiler chicks (n = 88) were immersed in pairs into 100% CO2 or exposed to CO2 gradual fill in a chamber with a displacement rate of 28% chamber volume per minute. Latency to performance of headshaking (HS) and gasping (GS) as potential indicators of distress, loss of posture indicative of insensibility, and the cessation of rhythmic breathing (CRB) and cessation of movement (COM) as the indicators of death were monitored (live focal sampling/video recordings). The duration and frequency of HS and GS were assessed. For both experiments, behavior data were analyzed for CO2 method and age (4 × 3 factorial). Age and CO2 concentration interacted for latency to CRB and COM, with longer latencies for 0-day-old chicks immersed into 70% CO2 than other concentrations and ages. CO2 concentration did not affect latency to HS, GS, or loss of posture but affected CRB and COM, with latencies longest for 70% and shortest for 90 and 100% CO2. Newly hatched chicks had a longer latency to CRB and COM and longer duration and frequency of distress behaviors than older chicks. At all ages, initiation of all behaviors occurred later with gradual fill compared to immersion. There was an increased duration and frequency of distress behaviors with gradual induction compared with immersion. Overall, immersion into 90 to 100% CO2 resulted in the shortest time to insensibility and death, with a decreased duration and frequency of distress behaviors. Chicks immersed into 70% CO2 had the longest duration of GS and time to death. Age affects the efficacy of CO2 euthanasia, with increasing age decreasing time to death and the duration and frequency of distress behaviors.

中文翻译：

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为新生儿和年轻肉鸡成功安乐死定义浸入二氧化碳气体的特性。

这项研究调查了禽舍内二氧化碳（CO2）的浓度如何影响CO2安乐死的功效以及CO2诱导方法的功效如何随着禽龄的增长而变化。在实验1中，将成对的雏鸡（n = 192； 0、3和6 D龄）浸入预先充满70％，80％，90％或100％CO2的室内。对于实验2，将3日龄和6日龄的肉仔鸡（n = 88）成对浸入100％CO2中，或将其逐渐暴露于CO2中，并以每分钟28％的腔室容积的速率进行填充。监测表现为摇摇欲坠（HS）和喘气（GS）的潜伏期，作为潜在的困扰指标，表示不敏感的姿势丧失，停止有节奏的呼吸（CRB）和停止运动（COM）作为死亡指标（实时焦点采样/录像）。评估了HS和GS的持续时间和频率。对于这两个实验，均分析了CO2方法和年龄（4×3阶乘）的行为数据。年龄和CO2浓度相互作用导致CRB和COM潜伏期，与其他浓度和年龄相比，浸入70％CO2的0日龄雏鸡的潜伏期更长。CO2浓度不影响HS，GS或姿势丧失的潜伏期，但会影响CRB和COM，潜伏期最长的为70％，最短的为90％和100％。新孵出的雏鸡对CRB和COM的潜伏期更长，遇难行为的持续时间和频率也比老年雏鸡更长。在各个年龄段，与沉浸相比，所有行为的发起都发生在逐渐填充之后。与浸入相比，渐进诱导的遇难行为持续时间和频率增加。总体，浸入90％到100％的CO2中可以缩短感性和死亡的时间，并减少困扰行为的持续时间和频率。浸泡在70％CO2中的小鸡的GS持续时间和死亡时间最长。年龄会影响CO2安乐死的功效，随着年龄的增长，死亡时间，遇难行为的持续时间和频率都会减少。