If only animals were equipped with some sort of claw or teeth shaped defenses, they could probably be released where they could be free and hunt for their food - if only there were such a places on earth....
Nah - it's better to just gas the ####ers or keep 'em in a cage until they rot to death.
There are statistics out there that show that domestic animals released into the wild can't survive. I know personally of city dogs gone feral who can kill birds, squirrels, cats but cannot get through the skin and hair.