Many commercial pet foods use rendered meat meals in their top five ingredients. They are almost always just a blend of extra crap that no one wants. Dead livestock, poultry, expired grocery counter meats, euthanized pets, road kill, and deceased zoo animals are all collected and pulled into a grinder. Often times, these meats have been dead for days & are rotting with maggots – meats that would never pass for human-grade food production
Once ground, the meats are all boiled in a large vat at very high temperatures. All the greasy fat rises to the top and is skimmed off the top. The rest is sent to a hammer-mill press, where the remaining moisture is squeezed out, leaving it a gritty powder. All nutrients and flavor are destroyed by the high amounts of heat, though it does not eliminate the toxins from plastic casings or euthanization drugs.
After all that grinding, processing, boiling, and skimming, manufacturers must add back synthetic vitamin & mineral packs after the high temperatures destroy whatever nutrients the raw materials contained. Additionally, palatants are added to the meal to make it smell and taste like real food to pets.