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.