A case study of ventilation shutdown with the addition of high temperature and humidity for depopulation of pigs.

In February 2020, a swine farm operating in multiple states throughout the Midwest began to evaluate emergency plans to respond to potential impacts of the COVID-19 pandemic. From February through April, extensive mitigation strategies were implemented in anticipation of market disruption. The farm consulted the AVMA Guidelines for the Depopulation of Animals to identify preferred methods for depopulation of swine; however, none of these methods were feasible. When the first US packing plant closed in April 2020 because of human COVID-19 infection, the farm began to evaluate whether ventilation shutdown plus (VSD+) could be used for depopulation. Through proof-of-concept trials, a method for ventilation shutdown with the addition of supplemental temperature and humidity was developed. A single location with 4 barns that could be retrofitted for the process was selected, and between April and June 2020, 243,016 pigs were depopulated (59,478 nursery and 183,538 finishing pigs). Mean ± SD time to silent (the time when no sounds could be heard and no motion seen) was 55.4 ± 14.5 minutes for the nursery pigs and 65.0 ± 18.1 minutes for the finishing pigs. Only 728 (0.300%) pigs required manual euthanasia at the end of the depopulation process. Efficacy exceeded AVMA recommendations for the use of VSD+ (> 95% mortality rate in < 1 hour). Findings could potentially guide the use of this method for mass depopulation in the event of a foreign animal disease outbreak or severe market disruption in the future.