Breathless Birds: Does air hunger impact the welfare of poultry at slaughter?

全球每年有720亿只鸡被屠宰。可控大气昏迷（CAS）越来越多地被使用，涉及暴露于气体混合物中导致逐渐失去意识，与电昏迷相比具有福利优势。商业CAS系统最常见的是将有意识的鸟类暴露在二氧化碳浓度增加的环境中。虽然避免了令人痛苦的二氧化碳水平，但这些气体会导致过度换气（深呼吸）反应，这在行为上是明显的。目前尚不清楚这种反应是否与人类在吸入二氧化碳时报告的呼吸困难和“空气饥饿”相对应。“空气饥饿”是一种强烈的、非常不愉快的经历，包括一种不舒服的呼吸冲动，与深刻的焦虑、沮丧和恐惧有关。如果在气体昏迷中使用的气体混合物导致鸡的空气饥饿，这构成了一个非常重要的福利问题，这让人质疑CAS是否是一种人道的屠宰前昏迷方法。鉴于哺乳动物和鸟类在解剖学和生理学上的差异，鸟类对空气饥饿的敏感性很难预测，而且以前没有研究专门研究过动物对这种感觉的感知。虽然一些早期的研究表明，鸡在某些情况下会避免二氧化碳，但现有的研究从未明确指出空气饥饿对这种避免的贡献，而且吸入一定浓度以上的二氧化碳是痛苦的，这一事实令人困惑。简单的行为方法（比如让鸟类离开含有二氧化碳的空间）是有缺陷的，因为二氧化碳是一种麻醉剂，可能会降低鸟类表达适当反应的能力。我们需要更复杂的行为方法，比如让鸟类在暴露于二氧化碳之后（而不是暴露于二氧化碳期间）表现出习得性厌恶，以及关注非痛苦浓度，以了解空气饥饿是否是一个福利问题。该项目的目的是确定鸟类在接触与商业屠宰相关的气体混合物时是否会出现空气饥饿。首先，我们将把鸡暴露在一系列代表不同CAS方法的相关气体混合物中，解开它们对二氧化碳和低氧水平的反应，这两种情况都会导致呼吸变化。我们将记录详细的行为和生理结果，以确定过度换气发生的条件，以及其明显特征和严重程度与气体类型和浓度的关系。然后，我们将通过评估鸡是否会避开和/或逃离与暴露于相关气体混合物相关的区域，来调查在CAS期间发生的过度换气是否代表一个福利问题。我们还将确定是否有任何自发行为与习得的回避行为相对应，以帮助我们了解哪些明显的呼吸困难迹象可能表明不愉快的呼吸经历。最后，我们将对大脑部分进行成像，以检查与恐惧、压力和焦虑相关的关键区域是否因暴露于相关气体混合物而被激活。总的来说，我们期望这些实验能够对过度通气的福利影响进行确证和强有力的评估。解决数十亿正在进行CAS的家禽是否经历空气饥饿的问题是极其重要的。我们提出的工作是开创性的，将使开发新的方法来检测动物的空气饥饿。无论结果如何，这项工作都将为全球未来的政策提供有价值的信息。如果我们的研究表明空气饥饿与家禽屠宰无关，那么CAS将被证明是一种高福利方法，它的吸收将得到加强。如果空气饥饿是明显的，结果将支持更人道的休克方法的发展，确保目前从电休克系统过渡到真正的福利改善。

Globally, 72 billion chickens are slaughtered each year. Controlled atmosphere stunning (CAS) is increasingly used, involving exposure to gas mixtures causing gradual loss of consciousness, with welfare advantages compared to electrical stunning. Commercial CAS systems most commonly expose conscious birds to increasing concentrations of carbon dioxide (CO2). Although painful levels of CO2 are avoided, these gases cause a hyperventilation (deep breathing) response which is obvious behaviourally. It unknown whether this reaction corresponds to the breathlessness and 'air hunger' reported by humans when inhaling CO2. Air hunger is a potent and deeply unpleasant experience, consisting of an uncomfortable urge to breathe which is associated with profound anxiety, frustration and fear. If the gas mixtures used in gas stunning cause air hunger in chickens, this constitutes a very significant welfare issue, calling into question whether CAS is a humane method of pre-slaughter stunning. Given the anatomical and physiological differences between mammals and birds, the susceptibility of birds to air hunger is difficult to predict, and no previous studies have specifically examined animal perceptions of this sensation. Although some earlier studies have demonstrated that chickens avoid CO2 in certain situations, the available research has never specifically addressed the contribution of air hunger to this avoidance and is confounded by the fact that CO2 is painful to inhale above certain concentrations. Simple behavioural approaches (such as allowing birds to leave a space containing CO2) are flawed since CO2 is an anaesthetic that is likely to reduce the ability to express appropriate responses. More sophisticated behavioural approaches such as those allowing birds to display any learned aversion after, not during, exposure to CO2, and a focus on non-painful concentrations are needed to understand whether air hunger is a welfare issue. The aim of this project is to determine whether birds experience air hunger during exposure to gas mixtures relevant to commercial slaughter. Initially, we will expose chickens to a range of relevant gas mixtures which represent different CAS methods, untangling their responses to CO2 and low oxygen levels, both of which cause respiratory changes. We will record detailed behavioural and physiological outcomes to determine the conditions under which hyperventilation occurs and how its apparent character and severity relates to gas types and concentrations. We will then investigate whether hyperventilation occurring during CAS represents a welfare issue by evaluating whether chickens avoid and/or escape areas associated with exposure to relevant gas mixtures. We will also deteremine if any spontaneous behaviour corresponds with learned avoidance behaviour to help us understand which apparent signs of breathlessness may indicate unpleasant respiratory experiences. Finally, we will image parts of the brain to examine whether key regions associated with fear, stress and anxiety are activated by exposure to relevant gas mixtures. Collectively, we expect these experiments to allow a corroborative and robust assessment of the welfare implications of hyperventilation.Tackling the question of whether air hunger is experienced by billions of poultry undergoing CAS is extremely important. The work we propose is ground-breaking and will enable the development of novel methodology to detect air hunger in animals. Whatever the findings, the work will provide valuable information to inform future policy globally. If our studies show that air hunger is not an issue relevant to poultry slaughter, CAS will be proven to be a high welfare method and its uptake will be enhanced. If air hunger is apparent, the results will underpin the development of more humane stunning approaches, ensuring that the current transition away from electrical stunning systems represents genuine welfare improvement.