Gas alternatives to carbon dioxide for euthanasia: a piglet perspective

Area of Science:

• Animal Welfare Science
• Agricultural Science
• Veterinary Medicine

Background:

• Current piglet euthanasia methods face public scrutiny regarding their welfare implications.
• Blunt force trauma, though scientifically supported as humane if done correctly, is visually distressing.
• Carbon dioxide (CO2) is commonly recommended but criticized for being aversive to pigs.

Purpose of the Study:

• To develop a scientifically validated approach-avoidance test to determine piglet aversion to gases.
• To evaluate the efficacy and humaneness of different gas mixtures for neonatal piglet euthanasia.

Main Methods:

• Utilized an approach-avoidance test where piglets freely chose between air and a chamber with gradually filled or prefilled gas mixtures.
• Tested various gas combinations including CO2, N2O, Ar, N2, and O2 in single-step and two-step euthanasia protocols.
• Monitored piglet behavior, including time to flailing and vocalization, to assess aversion and efficacy.

Main Results:

• All tested gas mixtures were aversive, causing piglets to leave the test chambers.
• Gradual fill methods showed less immediate aversion than prefilled chambers.
• A two-step method using N2O/O2 for anesthesia followed by CO2 euthanasia was slower but reduced squealing and flailing compared to CO2 alone.

Conclusions:

• The approach-avoidance test provides a piglet-centric method to assess gas aversion.
• No tested gas mixture was entirely non-aversive, but N2O/O2 offered an anesthetic effect.
• A two-step euthanasia protocol involving N2O/O2 anesthesia prior to CO2 immersion may represent a more humane alternative.