Colorado Bill Would Phase Out Heatstroke as a Poultry Depopulation Method

February 25, 2026

Washington, DC—The Animal Welfare Institute (AWI) welcomes yesterday’s introduction of the Modernizing Depopulation Act in the Colorado General Assembly. The bill would establish Colorado as the first state to phase out the use of ventilation shut down (VSD) and VSD plus heat (VSD+) as methods of depopulating (mass killing) flocks of chickens, turkeys, ducks, and other birds for disease control.  

Analogous to locking a dog in a hot car, VSD and VSD+ involve trapping thousands of animals inside a barn, closing off the airflow, and raising the temperature (the “plus heat” refers to the addition of heaters, humidity, or steam) as high as 130 degrees Fahrenheit until the animals die from hyperthermia or heatstroke—a process that can take several hours. These methods are not only cruel but also inefficient and often ineffective: Most poultry flocks depopulated with VSD+ have survivors who languish for hours or days before they are eventually found and killed by another method.

Sponsored by Assistant Senate Majority Leader Lisa Cutter (D-20), SB26-123 declares that depopulations of domestic poultry flocks for disease control purposes must be done as humanely as possible. The bill expresses the General Assembly’s opposition to the use of VSD and VSD+ and encourages use of higher-welfare depopulation methods. It establishes that, within three years of the law’s enactment, neither poultry owners nor state officials may authorize the use of VSD or VSD+ to depopulate poultry flocks for disease control.

“No one would tolerate putting down a companion animal by locking her in a hot vehicle. Yet that is exactly what has been done to millions of farmed birds in depopulations using VSD and VSD+,” said Susan Millward, executive director and chief executive officer of the Animal Welfare Institute. “The Modernizing Depopulation Act would position Colorado as a leader in phasing out these cruel practices while allowing the poultry industry a reasonable time to fully transition to more effective, higher-welfare alternatives.”

In the United States, VSD+ has been used at an alarmingly high rate to destroy poultry flocks infected with highly pathogenic avian influenza (HPAI, or “bird flu”) during the ongoing outbreak, which began in February 2022. Since then, the virus has been confirmed in over 900 commercial and 1,100 backyard flocks across all 50 states, leading to the depopulation of flocks totaling nearly 200 million domestic birds—mostly egg-laying hens. According to USDA records analyzed by AWI, as of November 2025, nearly 130 million birds—or about 72% of the birds for whom data was provided—had been killed in depopulations in which VSD+ was used for the entire flock or for birds in at least one barn on the premises.

During the current HPAI outbreak, depopulations in Colorado have killed the fifth-highest number of birds in the country, behind only Ohio, Iowa, California, and Pennsylvania. Since the outbreak began, 13 commercial flocks have been infected in the state, and more than 11 million birds have been culled as a result. This total includes nearly 6 million egg-laying hens killed in depopulations using VSD+. In three instances, a single Colorado farm depopulated a flock of over 1 million birds using VSD+ in combination with other methods.  

“Avian flu has plagued Colorado poultry operations for years. Sadly, depopulation events should not be regarded as unforeseeable emergencies, but as routine aspects of poultry production,” said Senator Cutter. “The Modernizing Depopulation Act would set Colorado apart in its commitment to farmed animal welfare through prioritization of more humane depopulation methods and a more modernized approach to disease control. There will be a day when torturing animals is unacceptable, and we can help lead the way.”

Alternatives to VSD and VSD+ include methods that use carbon dioxide, nitrogen gas, and high-expansion nitrogen-based foam. While nitrogen-based depopulation methods have not yet been used for disease control in the United States, they are available and approved for doing so, and they have been successfully deployed for this purpose in Europe and Canada. Because nitrogen can be easily extracted from the atmosphere and is used in many industries, it is inexpensive and readily available.  

The US veterinary profession supports a transition toward nitrogen-based depopulation methods. Furthermore, guidelines on animal depopulation recently released by the American Veterinary Medical Association recommend improved planning and preparedness for animal disease emergencies to help ensure that higher-welfare depopulation methods can be rapidly deployed in response to HPAI. The AVMA notes that using methods that minimize animal pain and distress also helps to alleviate the negative psychological impacts on veterinarians and others tasked with carrying out depopulations.