The 2022-2023 spread of bird flu has been the most catastrophic on record in the US. In less than two years, it’s hit hundreds of poultry factory farms across nearly every state in the country, costing the federal government $757 million and counting to manage, and the poultry industry more than $1 billion in lost revenue and other costs (experts also fear that the disease could spark an outbreak in humans). To help stamp out the disease’s spread, all of the more than 62 million chickens, turkeys, and other birds raised for meat and eggs on affected farms have been killed and disposed of, whether or not they actually had the virus, which can spread rapidly and has a very high mortality rate for poultry birds.

This fall, bird flu is surging again. So far in October and November, it’s infected dozens of factory farms largely in the Midwest, including on turkey farms raising animals for Thanksgiving season — resulting in the extermination of 4 million chickens and turkeys in just a month and a half.

I use the word “extermination” deliberately. Although many outlets have written that the birds on farms hit with bird flu are being “euthanized,” the reality of these mass killings is far from the painless end implied by that term.

Last year, I wrote a great deal about the rise of “ventilation shutdown plus” (VSD+), a method being used to mass kill poultry birds on factory farms by sealing off the airflow inside barns and pumping in extreme heat using industrial-scale heaters, so that the animals die of heatstroke over the course of hours. It is one of the worst forms of cruelty being inflicted on animals in the US food system — the equivalent of roasting animals to death — and it’s been used to kill tens of millions of poultry birds during the current avian flu outbreak.

As of this summer, the most recent period for which data is available, more than 49 million birds, or over 80 percent of the depopulated total, were killed in culls that used VSD+ either alone or in combination with other methods, according to an analysis of USDA data by Gwendolen Reyes-Illg, a veterinary adviser to the Animal Welfare Institute (AWI), an animal advocacy nonprofit. These mass killings, or “depopulations,” in the industry’s jargon, are paid for with public dollars through a USDA program that compensates livestock farmers for their losses.

In America’s peer countries, ventilation shutdown has been effectively banned because it’s so inhumane; last year, Danish bioethicist Peter Sandøe told me he was “shocked” by the method’s prevalence in the US and that in the European Union, relying on it would be illegal.

Thousands of US veterinarians, animal welfare experts, and animal advocates have protested the use of ventilation shutdown. But a growing body of evidence obtained through public records requests shows that the poultry industry, in partnership with agricultural and veterinary authorities, is quietly normalizing ventilation shutdown and planning its further use — even though the USDA’s own policy says it can only be used as a last resort.

Ventilation shutdown has become a go-to for the poultry industry

USDA regulations specify that VSD+ is meant to serve as a stopgap when one of two other depopulation methods aren’t available in time for producers to rapidly cull their farms: firefighting foam, which is sprayed over the birds to suffocate them, or carbon dioxide poisoning (neither of these is painless, especially the former, but both are widely considered less cruel than ventilation shutdown).

Glass Walls / We Animals Media

Glass Walls / We Animals Media

But getting access to these methods on short notice requires advance planning — having standing contracts with companies that can supply CO2 gas, for example — that neither the meat industry nor its regulators appear interested in ensuring is in place. VSD+, on the other hand, can more easily be arranged in a pinch because heaters can be rented off-the-shelf from equipment companies. When disaster strikes, livestock producers that failed to prepare can simply say they had no choice but to kill their animals with heatstroke.

“Failure to prepare is not a justification for using a less humane method,” a source who has worked in the livestock industry for decades and spoke on the condition of anonymity because of the professional repercussions of criticizing industry practices told me. Peer countries like Canada and those in the EU, the source pointed out, are doing fine in their bird flu response without resorting to mass ventilation shutdown (which isn’t to say that mass killings of animals by other means are humane because, among other reasons, they very often leave suffering survivors). In some European countries, nitrogen-filled foam, a newer, much less distressing technology that quickly renders birds unconscious and kills them through oxygen deprivation, has been used.

In the US, there have also been reports that livestock producers, especially massive factory farms that house hundreds of thousands or millions of birds on one site, prefer to use VSD+ because it’s logistically easier to deploy than other methods, requiring less staff and less cleanup.

Direct Action Everywhere

In February, Pennsylvania’s Department of Agriculture spent $119,000 to buy 14 heaters and related supplies to carry out ventilation shutdown plus during bird flu outbreaks, according to documents obtained in a public records request by AWI and shared exclusively with Vox. Producers seeking to kill their flocks with ventilation shutdown have generally tended to rent heaters on a one-off basis, but Pennsyalvania’s decision to buy a set of heaters suggests an intention to continue using the method. (The state is the country’s fourth-largest producer of eggs and eighth-largest producer of turkey.)

“We know VSD+ heat played a critical [role] in Pennsylvania in 2022 … We are entering a time of heightened risk, and with high [egg farm] density in Lancaster County, PA, need to know such resources are readily available for the region,” Pennsylvania’s former state veterinarian, Kevin Brightbill, wrote in an email to colleagues last December, discussing the need to procure heaters for ventilation shutdown. (This correspondence was also obtained by AWI.) In February, once the state ag department had made the decision to buy the heaters, Brightbill wrote in an email that they needed to come up with a “non-VSD based justification for purchase of this equipment.”

That last point is key — ventilation shutdown was never meant to be a default method, so emergency responders aren’t supposed to plan to use it routinely. The USDA’s rules are based on the American Veterinary Medical Association’s (AVMA) guidelines for depopulating animals, which classify ventilation shutdown plus as “permitted in constrained circumstances,” meaning it should only be used if less inhumane methods aren’t available. Preferred methods should be used for emergency response planning, the guidelines state, and “less preferred methods should not become synonymous with standard practice.” But that’s exactly what’s happened in the US poultry industry.

Now, with heaters in its emergency response arsenal, the marginal cost to Pennsylvania of using ventilation shutdown will be even lower.

“This just reinforces our impression that VSD is the ‘go to’ depopulation method and little serious attempt is being made by states to conduct the preparation needed to use preferred methods of killing,” Dena Jones, director of AWI’s farm animal welfare program, told me in an email. “Without continuing pressure from animal advocates, it’s likely that even more birds would be killed with this barbaric method.”

Bird flu “is still a very present threat to Pennsylvania’s $7.1 billion poultry industry,” Shannon Powers, press secretary for Pennsylvania’s Department of Agriculture, told Vox in an email responding to a request for comment on the heater purchase. “Each situation that involves making a decision to euthanize animals is evaluated individually to ensure American Veterinary Medical Association approved methods are chosen … Having equipment readily available in the event of an emergency can reduce response time, eliminating prolonged suffering by animals infected with a highly contagious, generally fatal disease, and preventing further spread of the disease.” (It’s worth noting here that, especially on large factory farms where animals are distributed among several large sheds, many of the birds killed for disease control purposes haven’t been infected with bird flu.)

Why some veterinarians are blaming their own profession

Many critics of ventilation shutdown have blamed the AVMA for enabling the practice. By classifying the method as “permitted in constrained circumstances” (a designation that then became federal policy) rather than recommending against it, they argue, the AVMA has made it possible for factory farms to kill vast numbers of animals with heatstroke and claim they’re doing it with veterinary approval.

The AVMA’s guidelines have helped create a situation in which “the poultry and egg industries lack any incentive to stop creating the precise ‘constrained circumstances’ in which the AVMA condones the inhumane method of VSD+Heat,” Reyes-Illg, the Animal Welfare Institute veterinary adviser, wrote in a letter to the AVMA in May 2022. “With the ‘easy’ method of VSD+Heat available to them, mega-CAFOs [or extra-large factory farms] are taking no measures whatsoever to enable the use of more humane methods.”

Despite these criticisms, the AVMA hasn’t changed its position on ventilation shutdown, and critics say the organization has prevented open discussion about the problems with the method. Last year, Cia Johnson, the head of the AVMA’s animal welfare division, told an audience of veterinarians and livestock producers, “Some of these methods are at risk of leaving the guidelines. I think you probably have an idea of what those methods might be. We need data to support them staying in the document.”

In January, I covered the growing movement of veterinarians who are challenging what they see as their profession’s alliance with the factory farm industry. Not long after, the AVMA denied admission to some veterinarians who are critical of VSD+ to its Humane Endings Symposium, a conference on animal kill methods.

“I’ve been an AVMA member for 11 years. It is my responsibility as a veterinarian to question our profession’s role in allowing public funding of heatstroke-based mass killing of millions of animals, a method that should be considered criminal animal cruelty,” Crystal Heath, one of the vets who were barred from the symposium, told me. “It is disturbing that such discussions are forbidden.”

The AVMA is now at work on the next edition of its depopulation guidelines. It’s unclear whether the classification of VSD+ will change, and the AVMA didn’t respond to a request for comment for this story.

But it’s clear that the current situation is untenably cruel — and that it just isn’t necessary. What we lack is not the technology, but the will and moral leadership in institutions like the USDA, the AVMA, and animal agriculture itself to change the norms in an industry that’s grown accustomed to unaccountable cruelty.

A version of this story originally appeared in the Future Perfect newsletter. Sign up here!