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

全球每年有720亿只鸡被宰杀。受控大气昏迷(CAS)被越来越多地使用，包括暴露在气体混合物中导致逐渐失去知觉，与电气昏迷相比，具有福利优势。商用CAS系统最常见的情况是将意识清醒的鸟类暴露在二氧化碳(CO2)浓度不断增加的环境中。虽然避免了令人痛苦的二氧化碳水平，但这些气体会引起过度换气(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吸入二氧化碳时所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、非常令人不快的经历，包括一种令人不适的呼吸冲动，这与严重的焦虑、沮丧和恐惧有关。如果用于气体昏迷的混合气体导致鸡的空气饥饿，这构成了一个非常重要的福利问题，使人质疑CAS是否是一种人道的宰前昏迷方法。考虑到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，之前没有任何研究专门研究动物对这种感觉的感知。尽管早期的一些研究表明，鸡在某些情况下可以避免二氧化碳，但现有的研究从未具体讨论过空气饥饿对这种避免的贡献，而且令人困惑的是，吸入超过一定浓度的二氧化碳是痛苦的。简单的行为方法(如让鸟类离开一个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，可能会降低表达适当反应的能力。要理解空气饥饿是否是一个福利问题，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在暴露期间表现出任何习得的厌恶，以及专注于不痛苦的集中。该项目的目的是确定禽类在接触与商业屠宰有关的气体混合物时是否会经历空气饥饿。首先，我们将把鸡暴露在代表不同CAS方法的一系列相关气体混合物中，解开它们对二氧化碳和低氧水平的反应，这两者都会导致呼吸变化。我们将记录详细的行为和生理结果，以确定过度通风发生的条件，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，我们将通过评估鸡只是否避开和/或与暴露在相关气体混合物中有关的逃生区域，来调查在CAS期间发生的过度通风是否构成福利问题。我们还将确定任何自发行为是否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，我们将对大脑的部分区域进行成像，以检查暴露在相关气体混合物中是否会激活与恐惧、压力和焦虑相关的关键区域。总而言之，我们希望这些实验能够对过度换气对福利的影响进行确凿和有力的评估。研究接受CAS的数十亿家禽是否会经历空气饥饿的问题是极其重要的。我们提出的这项工作是开创性的，将使开发新的方法来检测动物的空气饥饿。无论发现什么，这项工作都将为未来的全球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，CAS将被证明是一种高福利的方法，其接受度将得到提高。如果空气匮乏是明显的，结果将支持开发更人性化的令人惊叹的方法，确保目前从电力令人惊叹的系统的过渡代表着真正的福利改善。

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.