A couple of our friends bought us a book called eco dog.  In this book there is a quick recipe for creating a calcium supplement that dogs love.  All you do is take egg shells, put them in the microwave for 2 minutes to kill off any bacteria.  Then grind them into a powder and sprinkle it over your pets food.  1 egg shell has 2000 mg of calcium.  I just tried this with the eggs I used in a fritata and our dog loved the powder.