title: Nitrous oxide as a humane method for piglet euthanasia: Behavior and electroencephalography (EEG).
abstract: The search for humane methods to euthanize piglets is critical to address public concern that current methods are not optimal. Blunt force trauma is considered humane but esthetically objectionable. Carbon dioxide (CO2) is used but criticized as aversive. This research sought to: 1) evaluate the aversiveness of inhaling nitrous oxide (N2O; 'laughing gas') using an approach-avoidance test relying on the piglet's perspective, and 2) validate its humaneness to induce loss of consciousness by electroencephalography (EEG). The gas mixtures tested were N2O and air (90%:10%; '90 N'); N2O, oxygen and air (60%:30%:10%; '60 N'); and CO2 and air (90%:10%; '90 C'). Experiment 1 allowed piglets to walk freely between one chamber filled with air and another prefilled with 60 N or 90 N. All piglets exposed to 60 N lasted for the 10 min test duration whereas all piglets exposed to 90 N had to be removed within 5 min because they fell recumbent and unresponsive and then started to flail. Experiment 2 performed the same test except the gas chamber held N2O prefilled at 25%, 50%, or 75% or CO2 prefilled at 7%, 14%, or 21%. The test was terminated more quickly at higher concentrations due to the piglets' responses. Time spent ataxic was greater in the middle concentration gradients. Flailing behavior tended to correlate with increasing concentrations of CO2 but not N2O. Experiment 3, using the minimal anesthesia model, showed that both 90 N and 90 C induced isoelectric EEG, in 71 and 59 s respectively, but not 60 N within 15 min. The EEG results together with the observed behavioral changes reflect differences in the animal's perceptive experience. The implications for animal welfare are that N2O is much less aversive than CO2, and 90% N2O can euthanize piglets.
authors.affiliation: Animal Welfare Science Centre, Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Parkville, Australia. Electronic address: raultj@unimelb.edu.au.
authors.forename: Jean-Loup
authors.initials: JL
authors.lastname: Rault
authors.affiliation: Animal Welfare Science and Bioethics Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand.
authors.forename: Nikki
authors.initials: N
authors.lastname: Kells
authors.affiliation: Animal Welfare Science and Bioethics Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand.
authors.forename: Craig
authors.initials: C
authors.lastname: Johnson
authors.affiliation: USDA-ARS, Livestock Behavior Research Unit, West Lafayette, IN, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Dennis
authors.affiliation: AgResearch Ltd., Ruakura Research Centre, Hamilton, New Zealand.
authors.forename: Mhairi
authors.initials: M
authors.lastname: Sutherland
authors.affiliation: USDA-ARS, Livestock Behavior Research Unit, West Lafayette, IN, USA.
authors.forename: Donald C
authors.initials: DC
authors.lastname: Lay
mesh_terms: D000280:Administration, Inhalation; D000388:Air; D000827:Animal Welfare / Q000941:ethics; D000818:Animals; D001259:Ataxia / Q000139:chemically induced / Q000503:physiopathology; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000503:physiopathology; D002245:Carbon Dioxide / Q000008:administration & dosage; D004562:Electrocardiography; D000069280:Electrocorticography; D037901:Euthanasia, Animal / Q000941:ethics / Q000379:methods*; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009609:Nitrous Oxide / Q000008:administration & dosage*; D010100:Oxygen / Q000008:administration & dosage; D011581:Psychological Tests; D034421:Sus scrofa / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D009609:Nitrous Oxide; D010100:Oxygen
keywords: Aversive; Carbon dioxide; Death; Gas; Swine; Welfare