That is still an issue but blockchain-ish tech solves the "double spend of pig". I.e. you can't sell the same pig to many slaughter houses.
If I acquire some stolen pigs, or some pigs from a less than ideal lineage, I'll just enter them into the blockchain and say they're the result of breeding.
Blockchain works because it's verifiable. Breeding pigs, digging carbon (in its many forms) out of the ground, turning these things into other things isn't.