Decompression killing of laboratory rodents: a humane alternative to carbon dioxide?

啮齿动物是世界上使用最广泛的实验动物，每年有数百万只小鼠和大鼠被用于科学和医学研究。其中绝大多数是在研究期间或研究结束后被杀死的，最常见的方法是将它们暴露在不断上升的二氧化碳(CO2)浓度中。然而，以这种方式捕杀啮齿动物会引起重大的福利问题。研究表明，接触二氧化碳对啮齿类动物是有害的，因为它会导致焦虑、呼吸困难，超过一定浓度会引起疼痛。虽然研究人员研究了将啮齿动物暴露在二氧化碳中的不同方式，目的是减少这一过程对福利的影响，但有意义的改进空间似乎非常有限。人们迫切需要找到一种人道的方法来替代这种杀戮方法。在许多物种中，通过缺氧(体内组织缺氧)诱导意识丧失被认为是人道的，人们对低压缺氧(相当于迅速上升到高海拔的过程)作为一种高福利的杀戮方法的潜力越来越感兴趣。在逐渐减压的过程中，动物会因气压的低压缺氧而失去知觉，从而减少氧气的供应。虽然有证据表明啮齿动物也厌恶低氧，但这项工作是在惰性气体(如Argon)和快速低氧暴露条件下完成的。逐步减压提供了在不同的时间段内精细控制低压低氧暴露的手段，提高了人道死亡的可能性。我们有令人鼓舞的试点数据表明，低压缺氧有可能成为一种杀死实验室啮齿动物的方法，在福利方面优于逐渐暴露在二氧化碳中。这个项目的目的是系统地研究低压缺氧是否可以成为一种人道、可靠和有效的杀灭实验室杆状动物的方法。首先，我们将进行实验，以确定合适和有效的降压率，为小鼠和大鼠，使用麻醉的动物，以避免任何福利损害。然后，我们将在清醒的小鼠身上进行研究，以确定在暴露于候选减压曲线期间失去意识的时间，并特别寻找疼痛、焦虑和对这一过程的厌恶的迹象。这些研究将基于对生理反应和自发行为的测量，以及一项测试，在该测试中，我们将训练小鼠使用逃生门，如果它们希望离开它们认为厌恶的环境。减压小鼠的反应将与暴露在二氧化碳中的小鼠进行比较，方法与目前的实验室做法相同，以评估哪种(如果有的话)减压率明显更人性化。我们希望这些实验不仅能清楚地显示人们对不同杀戮方法的厌恶程度，还能让我们找出厌恶的潜在原因。如果我们的研究表明，低压缺氧作为一种人道的方法杀死老鼠是有希望的，我们将确定一条最佳的减压曲线，即比逐渐暴露在二氧化碳中引起更少的疼痛、焦虑和厌恶的曲线。如果我们的结果表明，逐步减压并不比二氧化碳更好，该项目将为低压缺氧提供一个明确的答案，结果还将提供有关二氧化碳对福利影响的新信息。作为一种潜在的人道替代方案，实验动物科学界广泛采用低压缺氧将产生深远的积极影响，使数百万(甚至数十亿)实验动物能够以较低的福利成本可靠地被杀死。这一结果也将使操作员受益，他们的法律和道德责任是尽可能人道地杀害实验室动物。此外，以最人道的方式扑杀实验室啮齿动物也将有助于提高公众对体内动物研究的接受度。

Rodents are the most widely used laboratory animals worldwide, and millions of mice and rats are used annually in scientific and medical research. The vast majority of these are killed either during or after the research, and the most common method is to expose them to a rising concentration of carbon dioxide (CO2). However, killing rodents in this way gives rise to important welfare concerns. Studies have shown that CO2 exposure is aversive to rodents because it induces anxiety, breathlessness and above certain concentrations, pain. While researchers have examined different ways of exposing rodents to carbon dioxide with the aim of reducing the welfare impact of this process, there appears to be very limited scope for meaningful refinement. There is an urgent unmet need to identify a humane alternative to this method of killing.Induction of unconsciousness by hypoxia (a deficiency in oxygen reaching body tissues) is considered to be humane in many species, and there is growing interest in the potential of hypobaric hypoxia (a process equivalent to rapidly ascending to high altitude) as a high welfare method of killing. During gradual decompression, animals are rendered unconscious by hypobaric hypoxia as air pressure and therefore oxygen availability is reduced. Although there is evidence that rodents also find hypoxia aversive, this work has been done with inert gases (e.g. Argon) and rapid hypoxia exposure rates. Gradual decompression offers the means to finely control hypobaric hypoxic exposure over variable time periods, improving the likelihood of a humane death. We have encouraging pilot data that suggests that hypobaric hypoxia has the potential to be a method of killing for laboratory rodents that is superior, in welfare terms, to gradual exposure to CO2. The aim of this project is to systematically investigate whether hypobaric hypoxia could be a humane, reliable and efficient method of killing for laboratory rodents.Initially, we will conduct experiments to determine suitable and effective decompression rates for mice and rats, using anaesthetised animals to avoid any welfare harms. We will then work on conscious mice to determine the time to loss of consciousness during exposure to candidate decompression curves and specifically look for signs of pain, anxiety and aversion to the process. These studies will be based on measurement of physiological responses and spontaneous behaviour, and also on a test where we will train mice to use an escape door if they wish to leave an environment that they find aversive. The responses of mice undergoing decompression will be compared to mice exposed to CO2 in the same way as current laboratory practice, to evaluate which (if any) decompression rates are demonstrably more humane. We expect these experiments to clearly show not just the extent of aversion to the different killing methods but to allow us to identify the potential reasons for aversion. If our studies show that hypobaric hypoxia has promise as a humane approach to killing of mice, we will determine an optimal decompression curve, defined as one which causes less pain, anxiety and aversion than gradual exposure to CO2. If our results show that gradual decompression is not better than CO2, the project will provide a definitive answer on hypobaric hypoxia and the results will also provide novel information on the welfare impact of CO2. As a potentially humane alternative, wide adoption of hypobaric hypoxia by the laboratory animal science community would have a profoundly positive effect, enabling millions (and potentially billions) of laboratory animals to be reliably killed with low welfare costs. This outcome would also benefit the operatives whose legal and ethical responsibility it is to kill laboratory animals as humanely as possible. In addition, the killing of laboratory rodents in the most humane way possible will also help to enhance public acceptance of in-vivo animal research.