The effect of age and method of gas delivery on carbon dioxide euthanasia of pigs

The objectives of this research were to evaluate the effect of age and delivering method during carbon dioxide (CO2) euthanasia on the welfare of pigs (Sus scrofa). In experiment 1, pigs aged 1, 2, 3, 4, 5, and 6 wk (n = 5 pigs/age) were placed in a chamber gradually filled with CO2 released at a flow rate of 20% chamber volume/min. In experiment 2, 3 week old pigs were placed in a chamber prefilled with 100% CO2 (n = 5). In both experiments, blood samples were collected prior to CO2 exposure and immediately after death to measure cortisol concentrations. Behaviours indicative of distress and insensibility were recorded continuously during gas exposure, included panting, open mouth breathing, righting response, escape attempts, loss of posture, muscular excitation and respiratory arrest. Cortisol concentrations were elevated in pigs after euthanasia with CO2 gas, regardless of age or gas delivery method. Age of pig did not affect latency to display panting, open mouth breathing, righting response, escape attempts, loss of posture, muscular excitation or respiratory arrest. Latency to display panting, righting response, escape attempts, loss of posture, muscular excitation and respiratory arrest was shorter when pigs were placed in a chamber prefilled with CO2 compared to pigs placed in a chamber then gradually exposed to CO2. Based on a shorter latency to loss of posture, which is considered an indicator of onset of unconsciousness, the prefill method of euthanasia appears preferable to the gradual fill method.