Not only calcium is present - but many other needed minerals. The RAW bone has the anti-oxidants and naturally occurring enzymes to help build a strong immune system and keep the dog's internal organs in good shape. Raw meat may indeed contain bacteria and parasites. However, a dog's gastro-intestinal system is constructed and functions much differently from that of a human, so generally, a dog can handle normal numbers of both bacteria and parasites 1. A dog's stomach acids are more powerful than human stomach acids, thus food is digested much more rapidly.
Most digestion takes place in the stomach.
A dog's intestinal tract is much shorter than man's, and digested food passes through more quickly, providing less opportunity for harmful bacteria and parasites to become established. As an added precaution, some members treat their raw meat with GSE or food grade H2O2 to eliminate surface bacteria such as salmonella or e. coli. There is a caveat to feeding raw food. IF your pet is not in good health, it may not be able to cope with the challenge of switching from commercial to raw food. A few members have reported serious problems when they started to switch sick animals to raw foods.