WIKIMEDIA, JASON SNYDERAbout a decade ago, a laboratory technician approached Daniel Weary with concerns about the way she was asked to put down animals. As was—and is—widely practiced across North America and around the globe, the lab tech would place rodents in a chamber and pipe in carbon dioxide (CO2) at increasing concentrations until the animals passed out and then died. “It’s not the best part of the job, killing animals,” Weary, who studies the welfare of dairy cows at the University of British Columbia, told The Scientist. “It’s a hard part of being a lab technician.”
Although some rodents stop moving upon exposure to CO2, others seem to become stressed. They might rear up, paw the sides of the box, or emit ultrasonic vocalizations. It seemed to the tech that the animals were suffering before losing consciousness. Her worries about the animals’ welfare have led Weary down a decade-long path to explore if rats and mice do indeed suffer from CO2 exposure, and if there are more humane ways to euthanize them. His results and those of others suggest that CO2 alone may not be as humane a killer as many once thought, and that giving the animals an anesthetic in advance of CO2 might ease their distress.
“There is compelling evidence that carbon dioxide is not good for the welfare ...
