Mass depopulation refers to the need of ending the life of large numbers of animals due to emergencies. This need could arise, for example, when we face disease epidemics (especially for pathogens that can transmit between humans and animals), and during natural disasters. A more recent application of depopulation was to reduce welfare issues associated with slaughter delays, which was observed in the United States in 2020 because of the Coronavirus disease (COVID-19) pandemic. In any case, depopulation should be conducted in a way that assures rapid and reliable unconsciousness followed by death.

The objective of this project was to summarize information on depopulation methods available to date specifically for swine, and to highlight gaps in knowledge to guide the focus of future research. To accomplish this objective, our research team searched several electronic databases to find peer-reviewed and non-peer reviewed papers on the topic. The timeline considered was from 1990 to 2020, and we included English publications from anywhere in the world.

We found 26 publications that were relevant to the topic of depopulation in swine. From those, the majority of research has been conducted with inhalable gaseous formulations (e.g., CO2), and there was a lack of research in methods such as the use of captive bolts, electrocution, and oral formulations. Furthermore, our literature review showed a lack of research in the areas of worker safety, worker emotional health, and on validation of animal-based measures to be used for depopulation welfare assessments.

Our conclusion was that a safe and reliable manner to induce unconsciousness and death for large populations of swine is lacking and urgently needed for preparedness purposes.
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Key Findings:

• Despite research over three-decades, a safe and reliable way to induce rapid unconsciousness and death in larger populations of swine is not available to the industry.

• There are very few studies on the topic of mass depopulation of swine, and available literature is inconsistent in regards to which details are provided
o For the future, minimum requirements for depopulation-type studies should include sample size/ age of animals, animal welfare, death and insensibility assessment methods, ease of carcass disposal, human safety assessment, personnel skill; and equipment and facility requirements.

• Further research is needed in the effectiveness of alternative methods for swine depopulation such as the use of water-based foam, sodium nitrate, and ventilation shutdown plus.