Calcium is one of the most challenging minerals for the animal body to utilize. Calcium from bone meal can be difficult for animals to fully digest. This is because the nutritional values of bone meal, which is typically in the range of 24% calcium and 12% phosphorus, are locked within relatively large particles. These particles are very slow to digest and most will likely pass through the body before much of their calcium can be absorbed into the body. Animal Essentials Seaweed Calcium on the other hand, is 34% pure calcium that is contained in very small, porous particles. This porosity allows digestive acids to permeate the particles so they can dissolve quickly in the stomach for more thorough digestion. Animal Essentials Seaweed Calcium also contains magnesium which is necessary for calcium absorption into the bone.
Here are two books I often recommend for people interested in feeding their dog or cat a home-made diet:
"Home-Prepared Dog and Cat Diets: The Healthful Alternative," by Donald R. Strombeck, DVM
"Dr. Petcairn's Complete Guide to Natural Health for Dogs and Cats," by Richard Pitcairn, DVM