Sodium nitrite was the poison i believe because of its high lethal dose rate to swine. I dont think it was ever approved for use here, but tested in a controlled environment in a few select places in other states...and im not a hundred percent sure if it ever happened. I know they were gonna test it in texas but public backlash had stalled it due to the hunters out there making money off hog hunts..so they dont want them gone..they want more pigs. I know one of the boys who was working on development of a distribution method via a special feeder. We had a lengthy thread on here about it probly a year or more ago..search it.