My BIL owned and operated a dead stock removal business for many many years. Quite obviously from the name of the business alone he picked up dead animals. Normally dead stock from farms or whatever else the farmer decided to throw into the pile. He stripped the hides off the animals for use in the garment industry (shoes, jackets, etc), the bones would go into bone barrels, blood into other barrels, the rest in even more barrels. Every second day or so all of this would be picked up for delivery to its' specified location. Most went to rendering plants to be used for pet food. Sound appetizing yet?
Just a few of the sites readily available for perusing.....
And my favourite line....... When was the last time you saw a cat in the middle of a corn field munching on a cob of corn?