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

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Controlled atmosphere stunning (CAS) is used in the slaughter of 38% of 72 billion chickens annually, with multiphase systems involving progressive exposure to CO2 being most common. While nociceptive activation in conscious birds is avoided, the extent to which hypercapnic and/or hypoxic stimulation induces unpleasant respiratory experiences is unknown. In humans, hypercapnic exposure is a potent stimulus of air hunger, the most profound and unpleasant form of dyspnoea. Currently, no animal models of air hunger exist. The aim of this project is to determine whether birds experience a negative affective state akin to air hunger during exposure to gas mixtures relevant to controlled atmosphere stunning.

We propose to characterise in detail the ventilatory response of hens to hypercapnia and hypoxia by exposing them to various gas mixtures while fully characterising physiological and behavioural manifestations of ventilatory drive. We will also map activated brain and brain stem regions by quantifying and comparing the expression patterns of the immediate early gene c-fos protein by immunohistochemistry in response to hypercapnic hypoxia, hypercapnic hyperoxygenation, and normocapnic hypoxia. We will determine the welfare implications of the hyperventilation caused by these gas mixtures by evaluating whether hens avoid and/or escape areas associated with exposure in two complementary behavioural paradigms. We will also explore associations between learned aversion behaviour and spontaneously expressed behaviour to validate potential markers of air hunger. In doing so, we will create a novel model for air hunger and robustly assess whether breathlessness is a welfare issue during CAS.
As well as being fundamentally important from the perspective of comparative vertebrate biology, this work addresses a major welfare question affecting billions of farmed birds. Its outcomes will be crucial to inform policy making and the direction of a global industry.