Evaluation of different gases and gas combinations for on-farm euthanasia of pre-weaned pigs

The aim of this research was to evaluate the welfare of pre-weaned pigs euthanised using three different gas treatments: 100% carbon dioxide (CO2), 100% argon (Ar) or a mixture of 60% Ar/40% carbon dioxide (Ar/CO2). Two studies (n = 5 piglets/treatment/study) were conducted: 1) behavioural and physiological data were collected from conscious piglets during exposure to test gases via immersion in a pre-filled chamber and 2) electrophysiological data were collected from lightly anaesthetised, intubated and mechanically ventilated piglets exposed to the same test gases. Based on the duration of escape attempts and laboured breathing, piglets exposed to 100% CO2 experienced more stress than piglets exposed to 100% Ar prior to loss of consciousness but there appeared to be no advantage to mixing Ar with CO2 on indices of animal welfare. However, spectral analysis of the electroencephalogram revealed no changes consistent with nociception during exposure to any of the three gas treatments. Based on the behavioural response to gas exposure, all gases tested caused signs of stress prior to piglets losing consciousness and hence alternative methods of euthanasia need to be evaluated.