You are correct; normally the animals are hit with isoflurane first (or similar), but that's not strictly required. Large culls are more routinely done with ju

You are correct; normally the animals are hit with isoflurane first (or similar), but that's not strictly required. Large culls are more routinely done with just CO2; I know of a few 100+ animals in a day culls, for example. Unrelated to lab animals, CO2 or N2 are both used for goose culls (e.g., https://cityroom.blogs.nytimes.com/2011/06/15/culled-geese-are-bound-for-tables-not-dump/ https://cityroom.blogs.nytimes.com/2011/06/15/culled-geese-a...) in part because it's humane and in part because the meat can still be processed and donated to shelters.