"Leftover foreign meat sources" sounds like something I wouldn't feed to pigs I like.
We've got to stop feeding rendered animal leftovers to herbivores, period. It's already a pretty well-established vector for prion diseases -- like BSE (mad cow), srapie and kuru. It's a pretty much ideal delivery method to infect livestock, because their immune systems aren't equipped to resist. They aren't built to ingest other animals.