The need for humane, effective and practical depopulation methods during disease outbreaks is great, especially with increasing outbreaks of highly pathogenic avian influenza in the U.S., foot-and-mouth disease in Europe and African swine fever throughout the world. Emergency depopulation is a difficult but necessary part of disease control, and traditional methods come with welfare, logistical and ethical challenges, explains Gabriela Grant, a student in the University of Minnesota College of Veterinary medicine.
“Depopulation is an unfortunate, but necessary, reality in swine production, and finding a method that prioritizes both efficiency and animal welfare is crucial,” Grant said during her student oral presentation at the American Association of Swine Veterinarians annual meeting. “Nitrogen foam is a promising solution, but there is still a lot to understand about its real-world application, effectiveness and impact on animal welfare.”
Grant set out to evaluate the different phases of this method to provide valuable insights to help veterinarians and producers make informed decisions in crisis situations. Her study focused on the before, during and after periods during use of high-expansion nitrogen foam for emergency swine depopulation.
Three Phases of Nitrogen Foam Depopulation
During phase 1 or “Before,” Grant and her colleagues studied the setup for nitrogen foam generation, including equipment, labor and logistical considerations for swine farms. Their experimental setup included an air compressor, which delivered highly pressurized air through a nitrogen membrane generator to extract nitrogen. This nitrogen was further pressurized before reaching containers leased to their team by HEFT international or compressed gas cylinders.
In phase 2 or “During,” they assessed how pigs responded to the foam, focusing on welfare indicators like time to unconsciousness and behavioral responses to ensure it was a humane method.
“Nitrogen-filled bubbles were pumped into airtight containers until the entire space was filled with foam,” Grant explains. “Then, a pulse of gas gets sent through the container to burst the bubbles, rapidly dropping oxygen levels to anoxic conditions. To ensure the pigs were dying from anoxia, and not from foam aspiration, we used a fluid scoring system ranging from 0 (no foam) to 4 (marked presence of foam in the respiratory tract), as determined by computed tomography and necropsy.”
Finally, in phase 3 or “After,” they evaluated the practicality of implementation by looking at carcass management through composting, environmental impact and producer/veterinary perceptions. They ran a 20-day composting study with three piles to examine how nitrogen foam might impact composting to industry standards with piles that contained nitrogen-foam depopulated pigs and captive bolt-depopulated pigs for their negative control.
“We tracked the number of days the piles maintained thermophilic temperatures between 104°F to 149°F, which is necessary for thermophilic bacterial activity and essential for effective decomposition,” Grant says.
Does It Work?
“The biggest takeaway from my research was that high-expansion nitrogen foam has a real potential as a humane depopulation method, but logistical and practical challenges must be addressed before it can be widely implemented,” she says.
From a welfare standpoint, she says this method effectively induces unconsciousness through anoxia rapidly, which may reduce stress compared to traditional depopulation techniques, such as carbon dioxide gas and ventilation shut down. Still, factors such as foam consistency, equipment efficiency, scalability and the need to be standardized need more research to ensure reliability across different farm settings.
“This research has the potential to directly benefit producers by providing a more humane, biosecure and practical method for emergency depopulation,” Grant says. “Traditional methods like CO2 gassing or ventilation have faced ethical concerns, a more humane alternative could improve consumer trust and regulatory compliance.”
She says nitrogen foam could be deployed directly on farms, allowing for faster, independent action rather than waiting for external resources. The goal is that producers could load pigs onto a specially equipped dump truck, drive to their compost site, foam the pigs and hold the dwell period for 12 minutes, and then proceed to dump and construct compost piles for an efficient beginning-to-end depopulation process.
“Mass depopulation is stressful for farmers and workers,” Grant says. ”This method has the potential to ease the psychological burden because it is hands-off – the dump truck gets covered with an airtight tarp, and the worker only needs to press the buttons to start the foam and then lift the back of the truck to unload the pigs after the process. As welfare regulations evolve, this research could shape future guidelines and prepare producers for industry changes.”
Grant was one of 15 students who competed in the oral presentation contest at the AASV annual meeting. Read more here.
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