After bones are cooked for bone broth (for 72 hours) the bones are removed, the cooked-out particles of bone marrow, cartilage, and bits of meat are strained off, then the broth and melted fat are separated and packaged accordingly.  That marrow and other bits don’t look very appetizing but carry all the same nutrition as the broth and tallow.  We blend it to a “mush” and freeze-dry it, which still doesn’t appeal to most people, but your fur buddies or chickens will love it.  Add a little to their regular diet and see what happens.