Ensuring humane deaths for laboratory birds

人道的实验动物处死方法是社会所期望的，也是维持公众对科学信任的必要条件。3R和成本效益分析的有力应用支持了涉及动物的研究的伦理批准，确保最小的危害与最佳的利益相权衡。附表1的处死描述了某些经批准的、被认为是人道的方法，通常作为组织收集科学研究的一部分，在研究工作结束时满足法律的要求，或作为转基因品系育种的常规部分。家禽（鸡）是英国用于实验程序的主要鸟类，2019年有124，078只家禽繁殖并用于实验程序（内政部，2019）。大量的小鸡在基因分型后的第一周内被杀死，用于饲养管理，或用于针对新生儿发育阶段的研究。目前允许的处理新孵化小鸡的方法是颈椎脱臼、暴露于浓度不断上升的二氧化碳（CO2）、脑震荡和麻醉剂过量。虽然这些附表1方法已在啮齿动物中进行了评估，但其在小型鸟类中的使用和可靠性的证据基础非常有限或不存在。事实上，在研究背景下，缺乏评估附表1在小于7日龄鸟类中的杀戮方法的已发表研究，尽管全球家禽业规模庞大，但农业环境中的相关研究也很有限。即使是对年长鸟类的研究也是在农场动物的背景下进行的，其中存在许多实际和食品安全限制-其中大多数与实验室环境无关。例如，缺乏关于接触浓度不断上升的二氧化碳对福利影响的研究，而一般的二氧化碳接触问题正变得越来越有争议。通过静脉注射过量麻醉剂与良好的福利结局相关，但很难在小型和/或幼鸟中进行，并且所涉及的处理可能会引起恐惧和痛苦。腹膜内注射与啮齿动物的组织刺激和死亡时间延长有关。暴露于惰性气体和低压缺氧（通过暴露于逐渐减压）在食物链中的成年鸟类中得到了积极的评估，似乎对小鸡有希望，但这些都不是目前可用的附表1杀死方法。其余物理方法：脑震荡和颈椎脱位（最常用）与成年鸡的可靠性和训练标准方面的重大问题有关，它们对新孵化的小鸡的福利影响尚不清楚。简而言之，没有或只有有限的证据显示，现行附表1所列的杀鸡方法与可接受的福利结果有关。本项目旨在填补这方面的知识空白，系统地评估现行和新的杀鸡方法对福利的影响（肉鸡和蛋鸡品系），（i）根据福利结果确认或拒绝当前方法;（ii）支持在附表1中增加新的人道方法。我们将整合行为，生理，神经生理和病理数据，以评估每种测试方法在意识丧失之前的痛苦类型和严重程度，这是我们在以前的工作中验证过的一种稳健方法。该项目将为新孵出的小鸡的宰杀方法提供详细、科学的指导，确保人道处死。这种指导将根据品种和年龄进行调整，改善研究设施中新孵化小鸡的福利。这一发现也可能对家禽肉类和鸡蛋生产的常规程序产生重要影响，这些程序定期扑杀小鸡。

Humane methods of killing for laboratory animals are expected by society and are essential for maintaining public trust in science. Robust application of the 3Rs and cost-benefit analysis underpins ethical approval of research involving animals, ensuring minimal harms are weighted against optimised benefits. Schedule 1 killing describes certain approved, assumed to be humane methods, commonly applied as part of scientific studies for tissue collection, to fulfil legal requirements on conclusion of the research work, or as a routine part of breeding of transgenic lines. Domestic fowl (chickens) are the primary bird species used for experimental procedures in the UK, with 124,078 birds bred and used in experimental procedures in 2019 (Home Office, 2019). Large numbers of chicks are killed in the first week of life after genotyping, for husbandry management, or in research targeted at the neonatal stages of development. Current permitted methods for despatching newly hatched chicks are cervical dislocation, exposure to carbon dioxide (CO2) in a rising concentration, concussion of the brain and anaesthetic overdose. While these Schedule 1 methods have been assessed in rodents, the evidence base for their use and reliability in small birds is extremely limited or absent. In fact, there is a dearth of published studies evaluating Schedule 1 killing methods in birds of less than 7 days of age in research contexts, and despite the scale of the global poultry industry, relevant research in agricultural settings is also limited. Even studies on older birds have taken place in the farm animal context, where numerous practical and food safety constraints apply - most of which are not relevant to laboratory settings. For example, there is a lack of research on the welfare implications of exposure to a rising concentration of CO2 and the issue of CO2 exposure in general is becoming increasingly controversial. Overdose of anaesthetic via intravenous injection has been associated with good welfare outcomes, but it is difficult to perform in small and/or young birds and the handling involved can cause fear and distress. Intraperitoneal injection is associated with tissue irritation and extended time to death in rodents. Exposure to inert gases and hypobaric hypoxia (via exposure to gradual decompression) have been positively assessed in adult birds within the food chain and appear promising for chicks, but these are not currently available Schedule 1 killing methods. The remaining physical methods: concussion and cervical dislocation (which is most commonly used) are associated with significant issues in terms of reliability and training standards in adult chickens and their welfare implications in newly hatched chicks are unknown. In short, there is either limited or no evidence that current Schedule 1 methods for chicks are associated with acceptable welfare outcomes.The aim of this project fills this knowledge gap by systematically evaluating the welfare implications of current and novel methods of killing of newly hatched chicks (of both broiler and layer strains), to (i) validate or reject current methods, depending on welfare outcomes; and (ii) underpin the addition of new humane methods to Schedule 1. We will integrate behavioural, physiological, neurophysiological and pathological data to assess the types and severity of suffering prior to loss of consciousness for each tested method, a robust approach that we have validated in previous work. This project will result in detailed, scientifically sound guidance for killing methods of newly hatched chicks, ensuring humane deaths. Such guidance will be tailored to strain and age, improving the welfare of newly hatched chicks in research facilities. It is also likely that the findings will have important implications for routine procedures in poultry meat and egg production, where chicks are regularly culled.