You’d be hard pressed to find someone who would argue that killing a flock of chickens by shutting down ventilation systems to their barn and letting them slowly overheat and suffocate is a pleasant way to go. In fact, a year ago, this method of killing sick birds—called ventilation shutdown—was not permitted by the Department of Agriculture. But after a devastating bout of highly pathogenic avian influenza (HPAI) decimated US chicken and turkey farms last year, the USDA approved and has started using this controversial killing technique to cull infected flocks at massive, commercial farms in an effort to prevent another outbreak.
Nobody is keen on killing hundreds of thousands of chickens at a time—aside from it being a grim task, it also results in a huge loss of revenue—but it’s a necessary evil to shut down disastrous outbreaks. The USDA acknowledges that ventilation shutdown is not a great way to go, though a representative told me the agency can’t say for sure how long it takes birds to die this way. The fact that the USDA would resort to a killing technique most experts agree is less-than-ideal at best and inhumane at worst, without fully understanding what this method does to the animals, shows how ill-prepared we are for dealing with a massive agricultural epidemic. If we want to be more prepared in the future, shouldn’t the USDA be looking for better ways to kill half a million birds at once?
When a flock of poultry is infected with HPAI, swift action is imperative. As long as the birds are alive, they actively shed the live virus through their feces and saliva, which increases the risk of the disease spreading to other farms. So when the virus is detected, the USDA requires the flock to be depopulated—a term meaning the mass killing of livestock in response to a disease outbreak—within 24 hours. In some cases, like on some turkey farms in Indiana last month, this means resorting to ventilation shutdown.
“I don’t think anyone denies that there are more welfare challenges with ventilation shutdown than any of the other techniques,” said Maurice Pitesky, a veterinarian and expert in poultry epidemiology at the University of California. “But if you’re just thinking solely about how to depopulate the flock, ventilation shutdown is the quickest way to do that.”
It’s true that, from a procedural standpoint, ventilation shutdown is the option that can be executed most quickly. Other methods, like gassing the birds with carbon dioxide or suffocating them with a dense CO2 foam, require more time to orchestrate: you have to find a way to get a CO2 tanker to the farm, pump the gas into the barn, and wait for the concentration to get high enough to depopulate the flock. Depending on the location and size of the farm, this could take more than 24 hours to complete—beyond the USDA’s deadline. Ventilation shutdown, on the other hand, is just a matter of flipping a few switches.
“It’s unheard of, the methods they’re applying."
The USDA guidelines for ventilation shutdown are to turn off the ventilation systems, then raise the temperature inside the barn to at least 104F for a minimum of three hours. This can be done by turning up the temperature, but because the barns are so densely packed they can sometimes heat up that much just by virtue of the air systems being shut off. It’s happened in the past by accident, when pranksters shut off power or electrical failures cause the air systems to shut down. From start to finish, the actual process is the quickest way to depopulate a flock.
The trouble is that, for each individual bird, it might be one of the slowest and most painful ways to die. Paul Shapiro, vice president of farm animal protection for the Humane Society of the United States, described the process as “essentially baking the birds to death,” and called it “horrific.”
The HSUS claims it could take birds hours to die through ventilation shutdown, but there are no studies that have looked at the time to death with this method. USDA officials have previously estimated the process takes 30 to 40 minutes to kill birds, but when I reached out to the agency, it couldn’t confirm how long it takes birds to die this way.
“The majority of birds will die quickly, but it is advisable to maintain the recommended temperature for three hours to account for poor heat distribution and, importantly, inactivate much of the HPAI virus in the poultry house,” Andrea McNally, a spokesperson for the USDA Animal and Plant Health Inspection Service, told me, stressing that ventilation shutdown was considered a last resort option. When I asked McNally to clarify what the USDA considered “quickly,” she said she couldn’t.
“The variabilities of structures and density of poultry make it hard to give you an easy answer,” McNally said.
It’s not all that surprising that the USDA doesn’t know precisely how long it takes birds to die via ventilation shutdown, because nobody really does, according to Patricia Turner, a veterinarian and pathobiology professor at the University of Guelph who has researched depopulation methods and is a consultant on the American Veterinary Medical Association’s depopulation panel.
“It hasn’t been studied, to be very honest,” Turner told me over the phone. “You want the animal to become insensible as soon as possible. The time to death is pretty rapid with ventilation shutdown, within probably 10-25 minutes depending on the size of the barn. The problem is that we don’t know what the animals experience in that time.”
One of the arguments in favor of using ventilation shutdown is that if farmers delay in an attempt to use another method like CO2, the virus could spread, putting even more animals on death row. But if there are other, potentially more humane methods, why aren’t we set up to put them in place quickly if needed?
“It’s unheard of, the methods they’re applying,” said Harm Kiezebrink, an expert in humane poultry depopulation who has developed painless slaughtering technology. “Anybody with a little common sense understands that if you don’t research animal welfare for a method that is now the standard, that is very, very bad.”
Kiezebrink has worked around the world to help governments manage avian influenza outbreaks, depopulating farms from the Netherlands to China. Ventilation shutdown isn’t widely used in other countries, according to Kiezebrink (gassing is usually preferred). It was green-lit in the UK in 2006 but never implemented. It’s far from the most gruesome depopulation method around—in the past, some countries have resorted to burning or burying birds alive—but Kiezebrink said the lack of understanding of the method’s effect on birds should rule it out, at least until further research is done.
"The public just might not have the stomach for it"
But other options aren’t cheap. The technology Kiezebrink once marketed—including a machine that kills birds instantly by dragging them through electrified water—cost as much as $600,000. Recently Kiezebrink said he’s been researching a nitrogen-based foam that would, he says, basically just put the birds to sleep when inhaled. But this, too, would likely be too expensive to use on a widespread basis.
“Gas-injected foam is better because the animals actually die of lack of oxygen, which occurs much faster and much more quietly—they don’t seem to show the same distress,” Turner told me. “The problem is nitrogen is expensive and difficult to source. For the huge farms prevalent in the US, which are much bigger than anything in Europe, it’s probably not feasible.”
So where does that leave us? The good news is, after the ventilation shutdown in Indiana, there haven’t been any more reports of HPAI so far this year. That buys us some time to work on more humane methods, including potentially developing vaccines, Turner said. She said when the AVMA completes its depopulation guidelines, the USDA will likely need to reassess its use of ventilation shutdown.
“I would be very surprised to see this technique accepted [by the AVMA] without peer-reviewed papers that support it,” Turner said. “In addition to needing data on it, there needs to be public acceptance. You can think of a number of procedures that might be very quick but would not be interpreted to be humane, or that the public just might not have the stomach for.”