
Slow down the metatbolism? What will -the marrow or the bones? Sounds very odd to me. For pups I will happily give raw meaty bones such as rib bones, but if you don't want the mess and smell of them indoors, what I always use for pups are the sterilised, filled calcium bones that you can pick up in pretty much any pet shop or even super market these days.
The other obvious and easy chew toy would be a stuffed Kong. My own dogs actually go mad for the Nylabones.