When I did online research of dog foods, it was pretty clear that the cheaper, low cost, foods often do include pet renderings. "animal by-product meal" was one of the "euphemisms" which appears on the label. I don't think those end up in the human food chain.

And I never heard of it helping with immunity.

No way a shelter could possibly "do" the processing. Cynic that I am, I suppose it may be a way for some shelters could make money. I mean, when I have my pet euthanized at the vet, it costs a bit even for the anonymous group burial. A high kill shelter is not getting paid for the burials, and is almost alwyas struggling for funds.

Ick, what a topic! But it is somethin we on PT think about it.