A Systematic Literature Review on Depopulation Methods for Swine

SIMPLE SUMMARY: Mass depopulation involves ending the life of large numbers of animals due to emergency situations, for example, disease epidemics and environmental disasters. Depopulation should be conducted in a way that assures rapid and reliable unconsciousness followed by death. Our review article aimed to summarize depopulation methods available for swine and to highlight gaps in knowledge to guide the focus of future research. Our findings showed that the majority of research has been conducted with inhalable gaseous formulations (e.g., CO(2)) and that 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. Finally, a safe and reliable manner to induce unconsciousness and death for large populations of swine is lacking and urgently needed for preparedness purposes. ABSTRACT: Swine mass depopulation refers to the destruction of large numbers of pigs and may include not only animals affected with a disease but also healthy pigs in a facility or surrounding areas. Emerging applications of mass depopulation include reducing welfare issues associated with slaughter delays, which was observed in the United States in 2020 as a result of the Coronavirus disease (COVID-19) pandemic. The objectives of this review were to summarize the available literature on swine depopulation methods and to highlight critical gaps in knowledge. Peer-reviewed articles were identified through a systematic search in electronic databases including Web of Science, MEDLINE, and PubMed. A total of 68 publications were assessed. Gaseous carbon dioxide inhalation was the most commonly reported depopulation method for both small- and large-scale trials. Measurements of consciousness state, which serves to assess suffering and humaneness, appeared to be lacking in a high proportion of the studies. None of the published studies demonstrated an ideally reliable and safe way to induce rapid unconsciousness in large groups of pigs. Development of rapid mass depopulation methods applicable to large groups of pigs is necessary to provide industry partners with suitable and low-cost emergency preparedness procedures while adhering to personnel safety and animal welfare standards. Lastly, there is an urgent need to standardize comprehensive reporting guidelines for depopulation studies.