Introducing breathlessness as a significant animal welfare issue

Abstract

Breathlessness is a negative affective experience relating to respiration, the animal welfare significance of which has largely been underestimated in the veterinary and animal welfare sciences. In this review, we draw attention to the negative impact that breathlessness can have on the welfare of individual animals and to the wide range of situations in which mammals may experience breathlessness. At least three qualitatively distinct sensations of breathlessness are recognised in human medicine--respiratory effort, air hunger and chest tightness--and each of these reflects comparison by cerebral cortical processing of some combination of heightened ventilatory drive and/or impaired respiratory function. Each one occurs in a variety of pathological conditions and other situations, and more than one may be experienced simultaneously or in succession. However, the three qualities vary in terms of their unpleasantness, with air hunger reported to be the most unpleasant. We emphasise the important interplay among various primary stimuli to breathlessness and other physiological and pathophysiological conditions, as well as animal management practices. For example, asphyxia/drowning of healthy mammals or killing those with respiratory disease using gases containing high carbon dioxide tensions is likely to lead to severe air hunger, while brachycephalic obstructive airway syndrome in modern dog and cat breeds increases respiratory effort at rest and likely leads to air hunger during exertion. Using this information as a guide, we encourage animal welfare scientists, veterinarians, laboratory scientists, regulatory bodies and others involved in evaluations of animal welfare to consider whether or not breathlessness contributes to any compromise they may observe or wish to avoid or mitigate.

Veterinary Forensic Pathology

“…The drowning process is complex, involving sequential, concurrent and overlapping cardiorespiratory reflexes, electrolyte and blood gas abnormalities, aspiration and swallowing of liquid, vomition, struggling, involuntary movements and physical exhaustion, breathlessness, or ''air-hunger'' 4 eventually culminating in death. 7 The central mechanism of drowning is rapid and persistent hypoxemia following the introduction of liquid at the entrance of the airway.…”

Assessing unconsciousness in livestock at slaughter

“…The aversive behaviours are considered a response to the CO 2 that causes irritation of nasal mucosal membranes and the fact that CO 2 is a strong respiratory stimulation that is known to induce a sense of breathlessness prior to loss of consciousness in humans Schwartzstein, 1995, Raj, 2006). It may thus form a serious concern for animal welfare, as breathlessness is considered unpleasant for the animal (Beausoleil and Mellor, 2015). Barfod (1990) and Erhardt et al (1989) on the other hand did not find conclusive evidence that CO 2 irritates the membranes and concluded that the observed gasping is not a sign of respiratory distress, but merely a normal response to the excessive CO 2 in the body.…”

“…Figure 3 shows that gasping occurred closely in time with retreat attempts. It may be assumed that gasping does compromise animal welfare in conscious pigs, because it is associated with a sense of breathlessness (Beausoleil and Mellor, 2015). Muscular contractions are observed in the majority of pigs exposed to high CO 2 concentrations and it has been heavily debated whether they occur before or after animals have lost consciousness.…”

“…Beausoleil and Mellor (2015) describe three different traits of breathlessness, namely: chest tightness, respiratory effort and air hunger, where air hunger occurs when the demand for ventilation exceeds the capacity to provide it (Parshall et al, 2012). This air hunger may occur when an animal continuously inhales high tensions of CO 2 and is a serious concern for animal welfare as it always unpleasant to the animal (Beausoleil and Mellor, 2015). Furthermore, there is much debate about what CO 2 concentrations are most aversive to pigs since behavioural responses of pigs vary with different CO 2 concentrations.…”

“…Carbon dioxide itself causes irritation of nasal mucosal membranes and is a strong respiratory stimulator that induces a sense of breathlessness prior to loss of consciousness in humans (Manning and Schwartzstein, 1995;Raj, 2006). Beausoleil and Mellor (2015) describe three different traits of breathlessness, namely: chest tightness, respiratory effort and air hunger, where air hunger occurs when the demand for ventilation exceeds the capacity to provide it (Parshall et al, 2012). This air hunger may occur when an animal continuously inhales high tensions of CO 2 and is a serious concern for animal welfare as it always unpleasant to the animal (Beausoleil and Mellor, 2015).…”