Stunning swine with CO2 gas: Controversies related to animal welfare

Abstract

The principal objective of this review is to characterize the physiological and biochemical events that occur in swine when stunned with carbon dioxide (C02) prior to slaughtering, as they relate to issues of animal welfare. Stress responses promote the maintenance of homeostasis and adaptation to the physiological and psychosocial challenges of a changing environment, a complex process that involves the coordinated activation of behavioural, autonomic and neuroendocrine reactions. When respired, C02 combines with water to form H2C03 (carbonic acid), which generates elevated concentrations of IT ions that result in a state of acidosis at the cellular level. Today, questions have been raised concerning animal welfare, as some fear that inhaling high concentrations of C02 may cause distress in animals before they lapse into a state of unconsciousness. In particular, the bodily movements observed in the early phase of C02-induced anaesthesia in swine have led to concerns about stress. Pigs exposed to 80% C02 for 60 sec experience lactic academia and respiratory and metabolic acidosis. Lactate levels are an indicator of stress, while it has been shown that blood lactate concentrations associated with pre-slaughter stress factors (e.g., aggressive handling immediately prior to stunning) have detrimental effects on pork quality. From the perspective of animal welfare, 90% argon by volume, or the lowest possible C02 concentration necessary to stun swine, is recommended. Argon is suggested as a welfare-friendly alternative to carbon dioxide for stunning/killing pigs and poultry. © 2012 Asain Network for Scientific Information.